Texas Earthquakes (Peter T. Flawn Series in Natural Resource Management and Conservation)

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TEXAS EARTHQUAKES

Number Two Peter T. Flawn Series in Natural Resource Management and Conservation The publication of this book was assisted by a University Cooperative Society Subvention Grant awarded by the University of Texas at Austin.

TEXAS EARTHQUAKES C L I F F F RO H L I C H A N D S C OT T D . D AV I S

Locations of earthquakes that have occurred in Texas or that were felt by Texas residents; numbers denote year of occurrence. Source: Data are from recent compilations of the authors, augmented by information from Davis, Pennington, and Carlson (1989).

UNIVERSITY OF TEXAS PRESS AUSTIN

The Peter T. Flawn Series in Natural Resource Management and Conservation is supported by a grant from the National Endowment for the Humanities and by gifts from the following donors: Jenkins Garrett Edward H. Harte Houston H. Harte Jess T. Hay Mrs. Lyndon B. Johnson Bryce and Jonelle Jordan Ben F. and Margaret Love Wales H. and Abbie Madden Sue Brandt McBee Charles Miller Beth R. Morian James L. and Nancy H. Powell Tom B. Rhodes Louise Saxon Edwin R. and Molly Sharpe Larry E. and Louann Temple

Copyright © 2002 by the University of Texas Press All rights reserved Printed in the United States of America First edition, 2002 Requests for permission to reproduce material from this work should be sent to Permissions, University of Texas Press, P.O. Box 7819, Austin, TX 78713-7819.

The paper used in this book meets the minimum requirements of ANSI /NISO Z39.48-1992 (R1997) (Permanence of Paper). Library of Congress Cataloging-in-Publication Data Frohlich, Cliff, 1947– Texas earthquakes ⁄ Cliff Frohlich and Scott D. Davis. p. cm. — (Peter T. Flawn series in natural resource management and conservation ; no. 2) Includes bibliographical references and index. ISBN 0-292-72550-7 (cloth : alk. paper) — ISBN 0-292-72551-5 (pbk. : alk. paper) 1. Earthquakes— Texas. 2. Earthquakes— Texas— History— Chronology. I. Davis, Scott D. II. Title. III. Series. QE535.2.U6 F76 2002 551.2209764 — dc21 2002004972

Table of Contents List of Figures, vi List of Tables, viii Preface, ix chapter 1 M E A S U R I NG E A RT H Q UA K E S , 1 chapter 2 E A RT H Q UA K E S I N T E X A S , 1 7 chapter 3 E A RT H Q UA K E S I N T H E U N I T E D STAT E S , 4 0 chapter 4 E A RT H Q UA K E S I N T H E WO R L D A N D OU T O F T H I S WO R L D , 5 2 chapter 5 C AU S E S O F E A RT H Q UA K E S , 6 5 chapter 6 P R E D I C T I NG E A RT H Q UA K E S , 8 2 chapter 7 S H OU L D I WO R RY A B OU T E A RT H Q UA K E S ? , 9 5 chapter 8 W H O A R E S E I S M O L O G I ST S A N D W H AT D O T H E Y R E A L LY D O ? , 1 0 3 chapter 9 A NEW COMPENDIUM OF E A RT H Q UA K E AC T I V I T Y I N T E X A S , 1 1 2 References, 257 Index, 269

List of Figures Frontispiece—Earthquakes Felt in Texas, 1847–2001, iii Figure P.1—The Quake Bowling Ball, x Figure 1.1—Modiﬁed Mercalli Intensity Scale, Level V, 3 Figure 1.2—Modiﬁed Mercalli Intensity Scale, Level XII, 4 Figure 1.3—Felt Area of 1811–1812 New Madrid Earthquake, 5 Figure 1.4 —Sample Seismogram, 7 Figure 1.5—Different Kinds of Seismic Waves, 11 Figure 1.6 —The “Swinging Gate” Seismometer, 13 Figure 1.7—Seismograph and Stereo Speaker, 14 Figure 1.8—Map of Seismograph Stations in Texas, 15 Figure 2.1—Billboard on Interstate Highway 35, 18 Figure 2.2—Earthquakes in Texas, by Region and Cause, 19 Figure 2.3—West Texas Structural Features, 20 Figure 2.4 —Felt Area—1931 Earthquake, 22 Figure 2.5—Felt Areas for the June 1978 and June 1980 Earthquakes, 25 Figure 2.6 —Texas Structural Features, 26 Figure 2.7—Felt Areas of Earthquakes Affecting Northeast Texas, 30 Figure 2.8—Felt Areas of Representative South-Central Texas Earthquakes, 33 Figure 2.9—Balcones Fault Red Granite Beer Label, 35 Figure 2.10 —U.S. Geological Survey National Seismic Hazard Mapping Project, 38 Figure 3.1—Big State Earthquake Contest, 41 Figure 3.2—Large U.S. Historical Earthquakes, 41 Figure 4.1—Uplift Zones for 1960 Chile and 1964 Alaska Earthquakes, 55 Figure 4.2—Deepest Large Earthquake, Felt at the Greatest Distance, 58 Figure 4.3—Map: 20th Century Earthquakes with Magnitude = 8, 59 Figure 4.4 —Total Destruction in Nicaragua and Vanuatu, 61 Figure 4.5—Yosio Nakamura, with Lunar Seismograph, 63 Figure 5.1—Explanation of Champagne Trick, 66 Figure 5.2—Explanation of Convection, 68 Figure 5.3—Enchanted Rock, 70 Figure 5.4 —Earthquakes beneath the Mississippi Fan, 71 vi

Figure 5.5—Histogram of Denver Earthquakes and Injection, 73 Figure 5.6 —Texas Quakes Triggered by Oil Production, 74 Figure 5.7—10 February 1959 Panhandle “Quake”, 80 Figure 6.1—Haicheng Foreshocks, 85 Figure 6.2—Earthquakes and Animal Behavior, 90 Figure 7.1—Aftershock Liqueur, 97 Figure 7.2—Should I Get Earthquake Insurance for My House?, 98 Figure 7.3—Earthquakes Don’t Kill People . . ., 99 Figure 7.4 —Earthquake Fountain Features, 102 Figure 8.1—Texas Seismologists at Work, 106 Figure 8.2—Greatest Living Seismologist, 110 Figure 9.1—Felt Area Map of 16 December 1811 Earthquake, 114 Figure 9.2—Felt Area Map for 22 October 1882 Earthquake, 118 Figure 9.3—Felt Area Map for 5 January 1887 Earthquake, 122 Figure 9.4 —Felt Area Map for 9 October 1902 Earthquake, 130 Figure 9.5—Felt Area Map for 8 May 1910 Earthquake, 133 Figure 9.6 —Felt Area Map for 28 March 1917 Earthquake, 136 Figure 9.7—Felt Area Map for 7 March 1923 Earthquake, 138 Figure 9.8—Felt Report Map from 30 July 1925 Foreshocks; Panhandle Names, 141 Figure 9.9—Felt Area Map for 30 July 1925 Earthquake, 143 Figure 9.10 —Focal Mechanisms for Some Signiﬁcant Texas Earthquakes, 148 Figure 9.11—Felt Area Map for 9 April 1932 Earthquake, 155 Figure 9.12—Felt Area Map for 12 April 1934 and 31 May 1997 Earthquakes, 157 Figure 9.13—Felt Area Map for 20 June 1936 Earthquake, 162 Figure 9.14 —Felt Area Map for 12 March 1948 Earthquake, 167 Figure 9.15—Felt Area Map for 20 June 1951 Earthquake, 170 Figure 9.16 —Felt Area Map for 9 April 1952 Oklahoma Earthquake, 172 Figure 9.17—Felt Area Map for 19 March 1957 Earthquake, 177 Figure 9.18—Felt Area Map for 28 April 1964 Earthquake, 183 Figure 9.19—Felt Area Map for January–March 1966 Events, 185 Figure 9.20 —Felt Area Map for 20 July 1966 and 15 February 1974 Earthquakes, 188 LIST OF FIGURES

vii

Figure 9.21—Felt Area Map for 9 December 1972 and 2 January 1992 Earthquakes, 196 Figure 9.22—Felt Area Map for 6 November 1981 Earthquake, 205 Figure 9.23—Felt Area Map for 23 July 1983, 3 March 1984, and 20 July 1991 Earthquakes, 209 Figure 9.24 —Felt Area Map for 9 April 1993 Earthquake, 219 Figure 9.25—Felt Area Map for 14 April 1995 Earthquake, 223 Figure 9.26 —Label from Ste. Genevieve Winery’s “Earthquake Red,” 226 Figure 9.27—Felt Area Map for 15 April 1995 Aftershock, 229 Figure 9.28—Felt Area Map from 24 March 1997 Earthquake, 234

List of Tables Table P.1— Questions about Earthquakes Answered in This Book, xii Table 1.1—Modiﬁed Mercalli Intensity Scale, 2 Table 1.2—Relationships among Magnitude, Fault Properties, and Moment, 9 Table 3.1—The 15 Largest Earthquakes in the United States, 42 Table 3.2—The 15 Largest Earthquakes in the Lower 48 States, 43 Table 3.3—U.S. Earthquakes in Which Damage Exceeded $100 Million, 44 Table 4.1—Global Rate of Earthquake Occurrence Larger than Given Magnitude, 53 Table 4.2—Twentieth-Century Earthquakes Resulting in Estimated Deaths Exceeding 100,000, 60 Table 5.1—Texas Earthquakes Occurring near Newly Constructed Dams, 77 Table 9.1—Explanation of Abbreviations for Different Magnitude Scales, 113 Table 9.2—Aftershocks of 14 April 1995 Earthquake in Alpine, Texas, 230 Table 9.3—Texas Earthquakes of Magnitude 3 or More, 240 Table 9.4 —Regional Earthquakes Felt in Texas, 251 Table 9.5—Unusual or Spurious Reports of Earthquakes, 253

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Preface The great pop artist Andy Warhol once said that in the future, everybody will be famous for ﬁfteen minutes. If you are a Texas earthquake seismologist, Warhol’s prophecy comes true every time a major earthquake occurs. So, what happens to a seismologist when an earthquake happens? Both the authors of this book, Scott Davis and myself (Cliff Frohlich), are seismologists, and this is what happened to us on Thursday evening, 13 April 1995. In Memphis, Tennessee, Scott had just come home from work when his pager started beeping, indicating that the United States Geological Survey had just reported a signiﬁcant earthquake. One of Scott’s ﬁrst tasks in his job at the University of Memphis seismological laboratory had been to develop a computerdriven telephone pager system to notify his colleagues automatically when scientiﬁcally interesting earthquakes occur. In this case, the pager display indicated that the earthquake had a magnitude of about 6.0 and had occurred in Texas. “Better call Cliff in Texas,” thought Scott, “and warn him before the fun begins.” Scott and I have been close friends ever since Scott was a graduate student at the University of Texas at Austin, researching earthquakes under my mentorship. However, when Scott called he spoke to my wife, who told him I wasn’t home. “Thursday is Cliff’s league bowling night,” she said. “I’ll tell him you called when he comes home.” A few minutes later, my wife got a second telephone call, this one from Walt Maciborski of TV station Channel 24 in Austin. “There’s just been a big earthquake in West Texas,” he told her, “and we need to speak to the University of Texas seismologist to ﬁnd out what he saw on the university’s seismograph. We’d like to interview him live on tonight’s ten o’clock news.” “Cliff isn’t here,” she said, “and he doesn’t know what’s on the seismograph. This is his bowling night, and he should be back in about an hour.” “He’s bowling?” said Maciborski. “You mean there was no one watching the seismograph when the earthquake happened?” No. And since the University of Texas doesn’t have a pager system, when a major earthquake occurs often the ﬁrst that we hear of it is from the TV stations when they call us asking for information. This earthquake had taken place in Alpine, Texas, about 500 km from Austin, and no one in my bowling league felt it. I wish I could tell you that we were bowling when suddenly bowlers on all forty lanes got a strike at the same time. But it didn’t happen that way. When I got home I called Maciborski, and we arranged to meet at the University of Texas geophysics laboratory for the interview. I then rushed out to the lab and got on the Internet to ﬁnd out everything I could about the earthquake. ix

Figure P.1. The Quake bowling ball. The Columbia 300 factory of San Antonio, Texas, is one of the nation’s largest manufacturers of bowling balls. In 1995 the company introduced three balls with an earthquake theme into its product line—the Quake, the Aftershock, and the Tremor. Advertisements for the Quake (shown here) promise that it will “shake your game to the core.” One of this book’s authors (Frohlich) used a Columbia Quake for league bowling in 1996 and 1997 and averaged about 185. Photo by Cliff Frohlich.

Fortunately, the earthquake wasn’t that big and it had occurred in a sparsely populated region. Nobody was killed and there wasn’t much serious damage. Unfortunately, the University wasn’t operating a seismograph at this time. The old Austin seismograph station had been ﬂooded out sometime earlier in a major rainstorm, and rather than repair it, we decided to begin installing new ultramodern equipment in a salt mine near Houston. Because there was no working seismograph, Maciborski and his assistant set up cameras in the parking lot outside the institute and prepared to interview me there. “You’re the director of the institute, right? Or are you just a professor?” he asked me. “Neither,” I told him. “I’m a research scientist, one of about twenty who work here, and one of about three who specialize in earthquake research.” Maci-

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borski was obviously disappointed—no professors involved, only so-called scientists whose seismograph didn’t even work and who are out bowling instead of ﬁxing it. What a bunch of losers. At ten o’clock the earthquake was Channel 24’s main news story. News anchor Bob Karston said, “Our phones have been ringing off the hook. It is the talk of the town. The state is all shook up over the ﬁrst earthquake to happen in Texas in over sixty years. There are no reports of injuries. But police report people felt it in Dallas, in San Antonio, and of course, in Austin.” There were clips from excited students in Austin. One young man happily said, “The room just started shaking, the ﬂoor was moving, it was pretty wild.” His dark-haired female companion said, “I had, like, my feet up on another chair so I was completely shaking.” Then: Bob: “Walt Maciborski joins us now live from the Institute for Geophysics in north Austin. Walt, were the scientists as surprised as everybody else was by this earthquake tonight?” Walt: “Yes, they were, Bob, and in fact they weren’t even in their ofﬁces. And there are seismographs in the hall here, but they were turned off; they’re waiting for some state-of-the-art equipment to be installed in here. So they didn’t get it on their instruments. But they did pull it up on some computers and showed some pretty interesting graphs from Albuquerque, New Mexico. I’m joined now by Senior Research Scientist Cliff Frohlich, who looked at this quake and has some opinions on it. First, how common or uncommon is it for us to feel the quake here in Austin?” Cliff: “Well, I guess the secret’s out. You know, earthquakes do happen and sometimes they’re felt in Austin. We don’t feel earthquakes in Austin more than, say, once every ten, twenty years. The 1985 Mexico City earthquake was felt here in some tall buildings, but that’s the most recent one that I can remember.” Walt: “Now, how does this quake compare to other quakes in West Texas or Texas?” Cliff: “Well this one would be the second biggest earthquake in Texas history. The biggest earthquake, which had a magnitude of about 6, was also in West Texas in 1931. So this quake is number two.” Walt: “Now, Austin is on the Balcones Fault, right? Would today’s earthquake affect our fault and maybe create an earthquake here?” Cliff: “Well, just because there’s a fault doesn’t mean there’s earthquakes. The Balcones Fault was active millions of years ago, so right now, it’s a dead fault. We don’t expect earthquakes on the Balcones Fault.”

PREFACE

xi

Table P.1 / QUESTIONS ABOUT EARTHQUAKES ANSWERED IN THIS BOOK TEXAS

Are there earthquakes in Texas? iii, 17–39, 112 –250 How can there be earthquakes in Texas? 69 –70 How serious is the Texas earthquake hazard? 36 –39, 41, 50, 98, 100 –101 How should Texans prepare for earthquakes? 98 –99 Should Texans purchase earthquake insurance? 96 –98 Should we expect earthquakes along the Balcones Fault? 35 Are any Texas earthquakes caused by petroleum production? 75 Are there any reservoir-induced earthquakes in Texas? 76 –78 Where are earthquakes likely to reoccur in Texas? 19 Where are seismograph stations in Texas? 15 What important questions about Texas earthquakes are unanswered? 105 –107 Has a tidal wave ever struck anywhere along the Texas Gulf Coast? 101 (continued)

Walt: “So how closely are you going to monitor this earthquake? And what’s next?” Cliff: “What’s next? Well, we’re going to try and get any data we can and learn more about it. Earthquakes in Texas are rare enough that every one of them is interesting.” Walt: “OK. Thanks for your time. I’m here at the Institute of Geophysics in north Austin as researchers try to make sense of this quake that we felt here in Austin. Bob?”

Suddenly, my ﬁfteen minutes of fame was over. The way my colleagues heard it, the main news story seemed to be that we seismologists weren’t in our ofﬁces and that our equipment didn’t work. And I hadn’t managed to tell Texans much of anything about earthquakes. How common are earthquakes in Texas? Do any Texans face real danger from earthquakes? Is California falling into the sea? How big was the biggest earthquake ever? Can we predict earthquakes? Can animals sense earthquakes before they happen? Why is a seismologist working in Texas? The purpose of this book is to answer these and other questions (see table P.1). You, our readers, are anyone who wants to know more about earthquakes. You might be a homeowner or businessperson who wonders whether you should worry about damage from earthquakes. You might be a student thinking about a career in earth science. Or you might be just another curious Texan. This book also has another, more archival purpose. In chapter 9 we present summary information about all known earthquakes that were strong enough to be felt by Texans. We have been careful to include explicit references to original sources such as contemporary newspaper articles; you may wish to look up xii

T E X A S E A RT H Q UA K E S

Table P.1 / (continued) THE WORLD

What earthquake caused the most deaths? 58, 60 What was the biggest earthquake ever? 54 –56 What earthquake was felt at the greatest distance? 57–58 What is the most significant earthquake in history? 60 – 61 What was the largest deep earthquake? 57–58 Which country has the most earthquakes? 52 Are earthquakes becoming more frequent? 54 Are there earthquakes on the moon? 61– 63 Are there earthquakes on Mars? 62, 64 Are there earthquakes on other planets? 62 – 63 Do earthquakes occur at all depths? 69 How frequent are big earthquakes? 23 How many earthquakes occur each year? 53 Is California falling into the sea? 80 HAZARD

Which states face the greatest earthquake risk? 40 – 41 Which country faces the greatest earthquake risk? 52 Where can I get earthquake hazard maps? 16, 102 Does my homeowners insurance cover earthquake damage? 95 Where can I purchase earthquake insurance? 96 Why don’t more insurance companies offer earthquake insurance? 96 Is earthquake insurance a rip-off? 96 –97 How can I make my home earthquake-safe? 98 –99 Why is earthquake damage sometimes worst far away from the epicenter? 62 Should there be laws to make buildings earthquake-safe? 100 What makes an earthquake very damaging? 57– 60 Is it safe to drill for oil? 36 Is it safe to move to California? 45 (continued)

PREFACE

xiii

Table P.1 / (continued) PREDICTION

Can earthquakes be predicted? 82 – 86 Can we predict earthquakes by watching how animals behave? 90 –91 What precursor is best? 91–92 When will the “Big One” occur in California? 83 What is the proper response to an earthquake prediction? 86 – 88 Do seismologists know how to predict earthquakes? 85 – 86 Since scientists can predict hurricanes and some volcanic eruptions, why not earthquakes? 93 CAUSES

What is necessary for an earthquake to occur? 65 What causes the plates to move? 67– 68 Since plate tectonics is a theory, doesn’t that mean it might be wrong? 71 How does fluid injection cause earthquakes? 72 –73 Why don’t earthquakes occur constantly? 66 – 67 Do tectonic plates float on a sea of liquid rock or magma? 70 Do tidal forces cause earthquakes? 78 How can rock flow? 67 How do you build a seismograph? 14 How does a seismograph work? 10 –14 PEOPLE

What do earthquake seismologists study? 103 –104 What makes seismologists mad? 8 Who is the greatest seismologist of all time? 109 –110 Are there any famous female seismologists? 110 –111 How does one become an earthquake seismologist? 107–109 What do earthquake seismologists do on a typical day? 104 How do we study earthquakes that happened long ago? 107 What do seismologists do in Texas? 105 –107

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some of these articles if you want to know more about earthquakes near where you live. Often they are the best sources of information about individual earthquakes. And many of the articles are just plain interesting—some because their viewpoints reﬂect just how much Texas culture has changed over the years, and others because their small-town ﬂavor is just plain goofy. Chapter 9 is not highly technical. However, it is the most thorough and complete historical summary available about earthquake activity in Texas. As such, it is valuable as a reference for scholars and useful as background material for public ofﬁcials who may need to set policy guidelines concerning seismic risk. We, the authors, take full responsibility for the material presented here. However, this book wouldn’t have been possible without the contributions and support of many other people. We are especially indebted to our friend Wayne Pennington. About twenty years ago Pennington initiated the original project that produced much of the research published here and personally sparked our own interest in Texas earthquakes. We also thank Steve Carlson, Dave Dumas, James H. Dorman, Diane Doser, Harold Gurrola, Jay Pulliam, and Deskin Shurbet, who made important contributions to our knowledge of Texas earthquakes and have always been good colleagues. Much of the last chapter of this book leans heavily on research originally performed by Davis, Pennington, and Carlson and was published in 1989 by the University of Texas Bureau of Economic Geology as a microﬁche attachment to a pamphlet entitled “A Compendium of Earthquake Activity in Texas.” Many individuals and organizations have been supportive of this project. The current impetus to update “Compendium” information came when the Texas Division of Emergency Management (DEM) asked us to perform a preliminary assessment of seismic risk in Texas and helped us obtain ﬁnancial support for this from the U.S. Federal Emergency Management Agency. We are indebted to Chovy and Tom Frohlich,1 who were responsible for most of the illustrations and photographs. We also thank Diane Doser and one anonymous reviewer, who were kind enough to carefully review an earlier draft of this book and correct many of our mistakes. Because the careers of both this book’s authors have beneﬁted from Peter Flawn’s leadership, it is highly appropriate that this book has been chosen for the Peter T. Flawn Series in National Resources Management and Conservation. In 1978, when one of this book’s authors (Frohlich) began his employment at what is now called the University of Texas Institute for Geophysics, Peter Flawn was its director. Flawn was president of the University of Texas and a faculty memPREFACE

xv

ber in the Department of Geophysical Sciences from 1982 to 1989, when the other author (Davis) fulﬁlled the requirements for a doctorate in that department. Flawn’s unwavering commitment to the institute, the department, and the Bureau of Economic Geology played an essential role in the founding in 2001 of the Jackson School of Geosciences, which now supports and oversees all three organizations. Finally, we are grateful to our friends and families for their encouragement during this project. Note 1. Tom and Chovy Frohlich are two of Cliff Frohlich’s children. Tom is a commercial photographer based in Seattle. Chovy Frohlich took art courses at the Rhode Island School of Design while attending Brown University. Presently she is a social worker in Chicago.

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CHAPTER 1

MEASURING EARTHQUAKES When we hear that an earthquake has occurred, scientists ask the same basic questions that other people do: • How bad was it? Were people killed, and was there severe damage? • How big was it? Did its size alone make it unusual? • Where was it? Did it affect places where we have friends or where lots of

people live? Did it occur in a place where earthquakes occur often or somewhere that earthquakes have not occurred previously? To answer questions like “how bad” or “how big,” it helps to have quantitative measures—numbers that allow us to compare earthquakes in different places. Thus in this chapter we describe three important ways of measuring earthquake damage and size. We also explain how scientists determine where earthquakes have occurred. How Bad Was It? Modiﬁed Mercalli Intensity When an earthquake occurs near a heavily populated place, newspapers typically report the number of people injured or killed and the dollar value of damage done. These are apt measures of a quake’s human impact, but they aren’t very useful if we want to know how the earthquake itself compares to previous earthquakes. These measures are especially inadequate if we want to assess the potential hazard from future earthquakes. In many areas the population density changes regularly over time, as do the number and type of buildings and the quality of construction. Moreover, damage depends on the quake’s intrinsic size and on its distance from areas of high population density. When we ask, “How bad was the Valentine, Texas, earthquake of 1931?” the question is not precise. This question might mean we wish to know how intense the shaking was during that earthquake. Or we might wish to know how damaging an identical earthquake would be if it were to happen in the same place today. Finally, we might wish to know how a similar-sized earthquake would affect some other place like Dallas, were it to happen there next year. We could answer all three of these questions if we had some objective way of describing the intensity of ground motion at different places during the 1931 earthquake. In 1902 an Italian, Guiseppe Mercalli, suggested measuring intensity by evaluating reports of damage or by asking people what they experienced during an earthquake. Then he assessed this information and assigned a number (see table 1.1); for example, if the quake was just strong enough to wake up most people who were asleep, he assigned an intensity of V (ﬁgure 1.1). Mercalli 1

Table 1.1 / MODIFIED MERCALLI INTENSITY SCALE (adapted from Richter 1958) LEVEL

CHARACTERISTICS

I.

Not felt.

II.

Felt by persons at rest, on upper floors, or favorably placed.

III.

Felt indoors. Hanging objects swing. Vibration like passing of light trucks. May not be recognized as an earthquake.

IV.

Hanging objects swing. Vibration like passing of heavy trucks or sensation of a jolt like a heavy ball striking the walls. Standing cars rock. Windows, dishes, doors rattle. Glasses clink. Crockery clashes. In upper range of IV wooden walls and frames creak.

V.

Felt outdoors. Sleepers wakened. Liquids disturbed, some spilled. Small, unstable objects displaced or upset. Doors swing, close, open. Shutters, pictures move. Pendulum clocks stop, start, change rate.

VI.

Felt by all. Many frightened and run indoors. Persons walk unsteadily. Windows, dishes, glassware broken. Knickknacks, books, etc., knocked off shelves. Pictures knocked off walls. Furniture moved or overturned. Weak plaster and low-quality unreinforced masonry cracked. Small bells ring (church, school). Trees, bushes shake visibly or rustle audibly.

VII.

Difficult to stand. Noticed by drivers of cars. Hanging objects quiver. Furniture broken. Weak chimneys broken at roof line. Fall of plaster, loose bricks, stones, tiles, cornices, unbraced parapets, and architectural ornaments. Cracks in unreinforced masonry. Waves on ponds; water turbid with mud. Small slides and caving along sand or gravel banks. Large bells ring. Concrete irrigation ditches damaged.

VIII.

Steering of automobiles affected. Partial collapse of unreinforced masonry. Some damage to reinforced masonry unless specifically designed to resist lateral forces. Fall of stucco and some masonry walls. Twisting, fall of chimneys, factory stacks, monuments, towers, elevated tanks. Frame houses moved on foundations if not bolted down; loose panel walls thrown out. Decayed piling broken off. Branches broken from trees. Changes in flow or temperature of springs and wells. Cracks in wet ground and on steep slopes. (continued)

intensities are always given as Roman numerals—perhaps because Mercalli was Italian, but also so they aren’t confused with Richter magnitudes, which we will explain later. Mercalli’s scale is still used widely today, although it has been modiﬁed several times to account for geographic differences in building construction. The scale used now is called the Modiﬁed Mercalli Intensity scale, and to be explicit about this the numbers are preceded by the letters MMI. Intensities on the Mercalli scale range from MMI I to MMI XII or 1 to 12. MMI I and MMI II correspond to motions so subtle that most people don’t feel them. Those few who do sense something may just feel slightly queasy or notice 2

T E X A S E A RT H Q UA K E S

Table 1.1 / (continued) LEVEL

CHARACTERISTICS

IX.

General panic. Unreinforced masonry destroyed or heavily damaged; reinforced masonry seriously damaged. General damage to foundations. Frame structures, if not bolted, shifted off foundations. Frames cracked. Serious damage to reservoirs. Underground pipes broken. Conspicuous cracks in ground. In alluviated areas sand and mud ejected, earthquake fountains, sand craters.

X.

Most masonry and frame structures destroyed with their foundations. Some well-built wooden structures and bridges destroyed. Serious damage to dams, dikes, embankments. Large landslides. Water thrown on banks of canals, rivers, lakes, etc. Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly.

XI.

Rails bent greatly. Underground pipelines completely out of service.

XII.

Damage nearly total. Large masses displaced. Lines of sight and level distorted. Objects thrown into air.

Figure 1.1

MEASURING EARTHQUAKES

3

Figure 1.2

hanging objects gently swaying. The highest intensity, MMI XII, is reserved for situations in which the shaking produces accelerations stronger than the pull of gravity, and heavy objects like statues get thrown into the air (ﬁgure 1.2). After damaging earthquakes occur, seismologists interview people or use newspaper reports to construct maps indicating where people felt shaking of different intensities. Nowadays people who experience earthquakes can send Internet messages describing what they felt to the United States Geological Survey,1 and seismologists studying the events will incorporate this information into an intensity map (Wald and others 1999). For contemporary earthquakes, these maps are useful for engineers or planners who wish to assess “how bad it was” in different places and for different kinds of construction. However, sometimes it is possible to use historical reports to construct intensity maps for earthquakes that occurred a century or more ago (ﬁgure 1.3). Often, comparing intensity maps for contemporary and historical earthquakes is the only way to determine whether a historical quake was bigger or smaller than a modern one. How Big Was It? Magnitude On 25 March 1998, the world’s largest earthquake for 1998 occurred near the Balleny Islands, just offshore of Antarctica (Antolik, Kavarina, and Dreger 2000). 4

T E X A S E A RT H Q UA K E S

Figure 1.3. Felt areas of the New Madrid, Missouri, earthquakes of 1811 and 1812. Roman numerals indicate the intensity of shaking as indicated by the Modified Mercalli Intensity (MMI) scale. Intensities in the western portion of this figure are estimates, as this part of the United States was virtually unsettled at the time of the earthquake. An isoseismal is a line surrounding a region with intensity equal to or higher than a given value, such as MMI VI. In this figure, isoseismal lines east of the Mississippi River are from Nuttli (1973), and estimated isoseismals to the west are from Carlson (1984).

Since the nearest city was about 2,000 kilometers (km) distant in New Zealand, the quake caused no damage and apparently was not felt by humans. It was an insigniﬁcant event if we only measure earthquakes in terms of how they affect people. To borrow from the old philosophy question: “If an earthquake occurs and nobody felt it, did it occur at all?” Clearly, to maintain records of the world’s earthquakes we need some measure of earthquake size other than maximum intensity—big is not always bad, and bad is not always big. The most common such measure is magnitude. Charles Richter invented the ﬁrst magnitude scale in 1935 (see sidebar 1.1), which is why people often say that the “magnitude is 4.8 on the Richter scale.” MEASURING EARTHQUAKES

5

Sidebar 1.1 OTHER MAGNITUDE SCALES Since Richter invented magnitude in 1935, other seismologists have defined other magnitude scales. Each scale uses something different to determine earthquake size, for example, different earthquake waves or a different kind of seismograph. However, by design, the scales all agree fairly well, at least for mid-size earthquakes with magnitudes like 6.0. To distinguish between them, seismologists designate magnitudes with various combinations of the letter “m” and a subscript. Generally, they use M (uppercase) for scales that are more reliable for measuring very large earthquakes, and m (lowercase) for scales that are more reliable for small quakes: • M S—Surface-wave magnitude. This is the magnitude most like Richter’s magnitude; it is

the most common magnitude used for older earthquakes • m b—Body-wave magnitude. This is the most common magnitude used for small or very deep earthquakes • m N—Felt-area magnitude; determined by a formula from the surface area where the earthquake was felt. For quakes occurring before 1900, this is often the only magnitude available. • M w—Moment magnitude; determined by a formula from the scalar moment of the earthquake. When available, this is the most reliable magnitude for quakes of all sizes. For a more complete list of magnitude scales used in this book, refer to table 9.1.

He determined magnitude by measuring the amplitude of ground motion as recorded on a particular seismograph. This measurement was really easy— Richter simply used a ruler to measure the peak-to-peak size of the biggest waves on paper seismograms (ﬁgure 1.4). He then used tables to correct the measurement for instrument gain and the effects of distance. Magnitude is a “power of ten” scale, so that a 5.8 indicates ten times more ground motion than a 4.8; a 6.8 is 100 times more; a 7.8 is 1,000 times more, etc. The Richter scale deﬁnes magnitude only in terms of the amplitude of ground motion recorded on a seismograph. Thus there is no limit to how small or how large magnitude can be. A very tiny earthquake might have a magnitude of minus 2. And a very large event might have a magnitude of 8; for example, both the 1906 earthquake in San Francisco and the 1998 Balleny Islands earthquake had magnitudes of about 8. In principle an extraordinarily large earthquake might have a magnitude of 12. However, since magnitude is a power-of-ten scale there are practical limits. People seldom feel earthquakes with magnitudes smaller than about 2.0, and even very sensitive seismographs seldom record earthquakes with magnitudes smaller than minus 1 or so. The Chile earthquake of 1960 —the largest recorded since seismographs were invented about a century ago—had a magnitude Mw of 9.5. This is about as large as possible for natural earthquakes (see sidebar 1.2). To get a magnitude of 12 would require something entirely different than an ordinary earthquake—like a good-sized asteroid crashing into the earth.

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T E X A S E A RT H Q UA K E S

Figure 1.4. Observations of seismic waves. Seismogram recorded at the seismograph station in Hockley, Texas, for an earthquake that occurred in Alaska on 20 March 1999. Note that the seismic waves arrive in distinct packets or phases, labeled here as “P,” “S,” and “surface.” The surface waves have the largest arrivals and are used for determining the magnitude MS. The relatively sharp arrivals of the P and S phases make them useful for locating the earthquake focus. The earthquake’s epicenter is the point on the earth’s surface directly above the earthquake focus, that is, the location shown on maps.

How Big Was It? Scalar Moment To be most useful, any statistic such as magnitude should have three properties. It should be (1) easy to measure, (2) strongly correlated with the phenomenon of interest, and (3) not strongly correlated with other phenomena. Most familiar statistics satisfy at least one of these properties; few satisfy all three. For example, weight and height are the most common statistics reported for football and basketball players. Weight and height are easy to measure and often correlated with success in these sports, but we are all aware of very heavy or very tall people who are poor athletes. To measure mental ability, IQ is the most familiar statistic. However, while IQ is strongly correlated with success in school (at least), it is very difﬁcult to measure, especially if you try to evaluate people from different backgrounds. With respect to these three properties, magnitude is not a very good statistic. Measuring it is easy enough; essentially, this just involves measuring the biggest arriving signal on a seismogram. The problem is that when some very big earthquakes occur, their faults slip relatively slowly, and thus their biggest arriving signals are not as large as signals from earthquakes on much smaller faults that slip more suddenly. Moreover, since particular seismographs often are tuned to

MEASURING EARTHQUAKES

7

Sidebar 1.2 WHAT MAKES SEISMOLOGISTS MAD? The authors of this book are sick and tired of reading articles in newspapers that confuse intensity and magnitude or that say “the Richter magnitude is a measure of earthquake shaking on a scale of 0 to 10.” The next time this happens in your newspaper, please call the editor and complain. Magnitude is a measure of earthquake size, so that each earthquake has only one magnitude. Intensity is a measure of the amount of shaking at a place, so that each earthquake has many intensities corresponding to places where it was felt. To avoid confusion, intensities are always written as Roman numerals, like VI; magnitudes are always written as ordinary numbers, like 6 or 6.0. Theoretically, magnitude can take any number, including negative numbers like -3 or

numbers like 13. However, earthquakes with magnitudes smaller than zero are seldom felt, so you almost never hear about them, and, on planet Earth, natural quakes with magnitudes larger than about 9.5 just don’t happen. Intensities range only between MMI I and MMI XII, or “one” to “twelve.” MMI I corresponds to low-level motions, not felt by most people. MMI XII is reserved for situations in which the shaking the quake produces is so strong that it exceeds gravity and objects actually get thrown into the air. When that happens, don’t bother calling your local newspaper; it won’t be published again for some time.

record signals at particular frequencies, they underestimate magnitudes for quakes having their strongest signals at another frequency. Thus magnitude is not correlated very well with the length of the fault that ruptured or the amount of slip. For these reasons, in 1966 a seismologist named Keiiti Aki proposed a different measure of earthquake size that he called scalar moment (Mo), sometimes just called moment. Like magnitude, scalar moment can be determined directly from seismograms. As with magnitude, determining scalar moment involves correcting for the gain of the recording instrument and the effect of distance. However, in addition, the signal is manipulated to remove any other effects introduced by the seismograph; and the higher-frequency details of the signal are removed by ﬁltering to determine the average strength of the signal radiated along the whole length of the fault. This process is routine but not nearly as easy as determining magnitude. Also, moment is not a dimensionless power-of-ten scale with simple, small numbers like magnitude. Instead, it has units of force times distance, so that a typical magnitude 4 earthquake will have a scalar moment of a thousand trillion newton-meters, and a magnitude 8 might have a moment a million times larger (see table 1.2). Scalar moment does, however, have two important advantages over magnitude. First, scalar moment can be used to estimate the area of the fault that slipped to cause the earthquake. Indeed, the scalar moment is equal to the prod-

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Table 1.2 / RELATIONSHIPS AMONG MAGNITUDE, FAULT PROPERTIES, AND MOMENT (APPROXIMATE) FAULT DIAMETER

SLIP

SCALAR MOMENT* (NEWTON-METERS)

8

70km

7m

1 billion trillion

7

22 km

2.2 m

6

7km

70cm

5

2.2km

22cm

4

700m

7cm

3

220 m

2.2 cm

2

70m

7mm

1

22m

2.2mm

0

7m

0.7mm

1

2.2 m

22 mm

2

70 cm

70m

3

22 cm

22m

4

7 cm

7m

5

2.2cm

2.2 m

6

7mm

0.7 m

MAGNITUDE

1 million trillion

1000 trillion

1 trillion

1 billion

1 million

1 thousand

1

Note: This table assumes that all faults are circular, that fault slip equals fault diameter divided by 10,000, and that the earth’s rigidity is 30 billion Pascals. All these assumptions are only approximately true; nevertheless, they illustrate how real earthquake sizes depend on fault diameter. *The mks unit of scalar moment is the newton-meter. Although this has the same units as energy, an earthquake’s scalar moment is not the same as its energy.

uct of three factors, the surface area A of the part of the fault that slipped during the quake, the average slip S over this region, and the rigidity or stiffness (denoted by the symbol µ) of the rock along the fault.2 This is quite useful, since one can determine moment from a seismogram and then ﬁgure out what combinations of rupture area and slip might have caused the earthquake. This allows us to estimate typical fault dimensions for quakes of various magnitudes (table 1.2). Thus a magnitude of minus 6 with a fault diameter of 7 mm corresponds to a crack in your car windshield, which explains why you seldom hear about earthquakes with negative magnitudes. A magnitude zero corresponds to a fault about the size of a two-car garage. Very damaging earthquakes with magnitudes between 7 and 8 have slips of several meters occurring along faults with dimensions of tens of km.

MEASURING EARTHQUAKES

9

Figure 1.5. (Opposite) Types of seismic waves. When an earthquake occurs (top), waves such as P and S that travel through the earth’s interior (or body) are called body waves. Waves that travel along the surface are called surface waves. These two wave categories correspond to the different

types of waves familiar to swimmers (bottom). A belly flop from the diving board produces sound waves that travel through the water and are heard by underwater swimmers, and a splash wave travels only along the surface.

Second, unlike magnitude, scalar moment has the same value regardless of the instrument used to record seismic waves. There are not different moments for different kinds of seismographs (as in sidebar 1.1). For these two reasons, seismologists nowadays nearly always prefer to use moments rather than magnitude for measuring earthquake size. However, moments will never completely replace magnitudes, partly because magnitudes are just so familiar to the public and because moment numbers are so unwieldy. Where Was It? How a Seismograph Works For some earthquakes scientists have no problem ﬁguring out where they occurred. If a quake happens in a populated area and is large enough, felt-report maps such as in ﬁgure 1.3 present approximately circular zones around the region where the fault slipped. Indeed, for historical earthquakes occurring before about 1900, such maps are usually the only means of location available. But to locate earthquakes that occur in unpopulated regions or that are too small to cause damage, it is useful to employ a seismograph, a detector of seismic waves that is more sensitive than humans. The power of the seismograph is that it provides a way to sense and locate earthquakes that are far too small to be felt or do damage. When a fault slips suddenly, the disturbance travels away in all directions, much as waves on a pond travel away from the point where a pebble is dropped. Although a sizable portion of the fault may slip, the point where the slippage begins is called the earthquake focus; subsequently the area that slips grows larger as the rupture proceeds. A seismograph ampliﬁes and records the elastic waves produced by the sudden slippage. Since waves arrive earliest at the closest seismograph stations, and since different kinds of seismic waves (ﬁgure 1.5) travel at different speeds, you can locate the focus if you know the arrival times at several seismograph stations. For example, suppose that a station records a primary or “P” wave and a secondary or “S” wave (ﬁgure 1.4). Seismologists know that up to distances of 1,000 km, P waves travel at about 8 km per second (km/sec), and S waves travel at about 4.5 km/sec. Using high school math one can show that with these velocities, the epicentral distance in km is about ten times the difference in seconds between S and P arrivals. If the S arrives one minute after the P at a station, the

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T E X A S E A RT H Q UA K E S

Figure 1.5

MEASURING EARTHQUAKES

11

Figure 1.6. (Opposite) How a seismometer measures ground motion. The hinges on a properly hung gate are placed so that after you open it, gravity will slowly close it—if you forget (top). After each use, a poorly hung gate must be closed and latched because gravity tends to swing it open. In a “swinging gate” seismograph (bottom), a mass is hinged to a pedestal so that the mass swings like a properly hung gate. If the

wire that supports the mass is adjusted properly, it will swing very slowly when displaced. If the ground and pedestal move one direction, the mass swings in the opposite direction. To record the motion, a magnet is attached to the mass so that the swinging moves the magnet in and out of a coil of wire. The changing magnetic field within the coil induces an electric current that is amplified and recorded.

quake-to-station distance is about 600 km. If P and S readings are available from three or more stations, you can locate the focus. Before about 1960 seismologists often located earthquakes on a globe by drawing arcs around the sites of seismograph stations. Seismologists now use computer programs that take all available readings and ﬁnd the best-ﬁtting epicenter. How does a seismograph work? The essential element of a seismograph is just a loosely suspended object that, when the ground moves, can’t quite keep up. For vertical motion, this object is just a mass suspended from a spring. For horizontal motion, this can just be a “swinging gate” (ﬁgure 1.6). To make a working seismograph, the motion of the suspended object must somehow produce an electric current. A simple way to do this is to use the fact that when an ordinary magnet moves through a coil of wire, it induces an electric current in the wire. Thus if the seismograph mass is a magnet and the coil of wire is ﬁxed to the ground, the motion of the ground produces a current. After ampliﬁcation, even imperceptible ground motions produce signals that can be displayed with a suitable chart recorder or on a computer screen. A seismograph is just like an ordinary stereo speaker, but in reverse (ﬁgure 1.7). Your stereo speaker has a magnet and a coil of wire in it, with the magnet attached to the base of a cardboard cone. In the speaker, an electric current from your ampliﬁer through the coil makes the magnet move, vibrating the paper in the cone and making sounds—vibrations of the air. Speaker: electric current –> moving magnet –> vibration of air Seismograph: vibration of ground –> moving magnet –> electric current Several seismograph stations operate continuously in Texas (ﬁgure 1.8). In Hockley, Texas, a small town 50 km northwest of Houston, the University of Texas at Austin has placed modern seismic sensors about 500 meters beneath the surface in a salt mine operated by United Salt, Inc.3 The Hockley site is attractive for a seismograph station because its subsurface location reduces effects caused by manmade and weather-generated noise. In Lajitas, Texas, near Big Bend, Southern Methodist University operates a seismic array. A seismic array is several nearby seismograph stations operating together; arrays are especially

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T E X A S E A RT H Q UA K E S

Figure 1.6

MEASURING EARTHQUAKES

13

Figure 1.7. A seismograph and a stereo use the same principles. In a seismograph, ground motion moves a magnet into a coil of wire and induces an electric current, which, after amplification, is recorded. In a stereo a record, tape, or CD player produces an electric signal, which is amplified and sent to a coil of wire in the stereo speaker. A magnet in the speaker coil moves in response to the current, causing the shell of the speaker to move and make sound.

useful because they allow the detection of weaker signals and because scientists can use them to determine the direction of arrival of seismic phases from distant earthquakes. Elsewhere, in far West Texas the University of Texas at El Paso operates several stations, mainly to record small regional earthquakes. Texas Tech University operates stations in Lubbock and Amarillo, and Texas Tech and the University of Texas at Austin jointly operate a station in Junction, Texas. Finally, sometimes amateurs build and operate seismographs. This is a bit tricky—not the kind of thing most people could do for a high school science project. However, articles in Scientiﬁc American in September 1975, July 1979, and April 1996 explain how to do it (Strong 1975; Walker 1979; Carlson 1996). There is even a website that lists amateurs worldwide and archives the seismograms they record.4 According to this site, ﬁve amateurs were operating seismic stations in Texas as of this writing. 14

T E X A S E A RT H Q UA K E S

Figure 1.8. Seismograph stations in Texas. The circles are the sites of threecomponent stations operated by universities. The labels adjacent to each site are the official station codes—three- or four-letter names seismologists use to identify the station. The codes are: AMTX—Amarillo; BUTX—Baylor University; DAL—Dallas; EPT—El Paso; CGTX— Campo Grande Mountain; HKT—Hockley; JCT—Junction; LBTX—Lubbock; LTX—Lajitas; MDT—McDonald Observatory.

Notes 1. For the central United States, the USGS began the website to produce what are known as Community Internet Intensity Maps only in the year 2000. You can access this site at: http:// pasadena.wr.usgs.gov/shake/cus/. At this website you can contribute felt reports for recent earthquakes and view intensity maps for current and past events. 2. When a twisting or shearing force acts on any elastic solid, it will change shape until the force is removed, whereupon it springs back to its original shape. Some materials like steel or rock are very rigid; that is, they do not change shape much even when a large force is applied. Others, like foam rubber, are not very rigid. When scientists measure rigidity in the lab or use it in equations such as “scalar moment equals fault area times slip times rigidity,” they usually use the symbol µ,which is the Greek letter m. MEASURING EARTHQUAKES

15

Sidebar 1.3 CAN YOU VISIT A SEISMOGRAPH STATION? If you ask, most scientists who operate stations would probably let you visit. But there isn’t all that much to see. And often the seismic sensors themselves are in places where the public may

not go (for example, the salt mine at Hockley). However, many station operators around the United States routinely put their seismic data on their websites.

3. For the University of Texas’ Hockley station, you can see today’s data and pictures from down in the salt mine at: http://www.ig.utexas.edu/research/projects/eq/seismo/hkt/about/abouthkt .htm. Current data recorded at several stations in and near Texas are available at: http://www .ig.utexas.edu/TexSeis/. A website that includes a very complete set of links to various earthquakerelated sites around the world is: http://www.geophys.washington.edu/seismosurﬁng.html. The U.S. Geological Survey Earthquake Hazards program website includes maps of earthquake hazard, recently occurring earthquakes, and much other useful and interesting information: http://earthquake.usgs.gov/. 4. The so-called Public Seismic Network archives information from and about amateur seismologists; the web-address is: http://psn.quake.net. In July 2002 this site shows amateurs operating stations in Buda, Corpus Christi, Friendswood, Houston, Pearland, and Plano.

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T E X A S E A RT H Q UA K E S

CHAPTER 2

EARTHQUAKES IN TEXAS Are There Earthquakes in Texas? When people think of Texas, they seldom think of earthquakes. They think of hurricanes, tornadoes, ﬂoods, hailstorms, and droughts, but not earthquakes. On 25 October 1989 the Los Angeles Daily News ran a story about the safest places to live in the United States to avoid natural disasters. While the article did note that disasters could happen anywhere, the writer identiﬁed the town of Alpine, Texas, as one of the safest spots in the United States: According to seismologists, meteorologists, hurricane specialists and other specialists, a small area of west Texas and southeast New Mexico seems to be the most riskfree from natural disasters . . . In Alpine, Texas, where the population is 7,000, the only weather problems are a few hailstorms.

The St. Petersburg Times in Florida picked up the article and ran it on 29 October under title “Alpine, Texas. Earthquakes? Not here. Tornadoes? Hurricanes? Never heard of ’em. If you’re serious about avoiding natural disaster, this Southwest town is home sweet home.” If there are earthquake gods, they must have been listening because ﬁve and a half years later, on 14 April 1995, the second largest earthquake in Texas history occurred near Alpine. The magnitude 5.7 shock generated intensities in Alpine high enough to cause general alarm and minor damage: People ran from their homes and cars and screamed in confusion, residents said. Some thought it may have been an explosion, yet they realized it was an earthquake because it lasted so long. “We have an arts and craft store downtown that looks like a tornado hit it,” said assistant police chief Chris Croy. “I’m not going to say there’s a big panic, but everyone is concerned.” (El Paso Herald-Post, 14 April 1995) Croy noted the ﬁrst tremor seemed to set off every burglar alarm in the city . . . “I was scared to death, to tell you the truth,” he said. “I’d rather be shot at than be in another earthquake.” (San Angelo Standard Times, 14 April 1995) [Alpine] mayor Bill Sohl . . . was one of those who thought at ﬁrst he was having a heart attack when the Thursday quake hit. “I took two shots of Crown Royal and was back in shape,” he said. He and his wife were in the house when the shaking started, and they thought the boiler was about to blow up. “I told my wife to get out; then I saw the waves on the swimming pool and knew it was an earthquake. By the time we got the door, the shaking had stopped except for us.” (Pecos Enterprise online) Back in Alpine, people scurried from their homes and cars, some screaming. “The streets were lined with people,” said paramedic Mike Scudder. “It looked like a parade.” (Dallas Morning News, 15 April 1995) 17

Figure 2.1. Are there earthquakes in Texas? A billboard along Interstate Highway 35 between San Antonio and Austin proves that someone besides the authors of this book thinks so. Photo by Cliff Frohlich. Used with permission.

In addition to breaking gas mains and causing several small ﬁres, this earthquake also caused landslides on nearby Cathedral Mountain and was felt by individuals in the upper stories of buildings as far away as San Antonio, Austin, Dallas, and Oklahoma City. There are indeed earthquakes in Texas (ﬁgure 2.1). It is a puzzle to the authors of this book why the journalist who wrote the Los Angeles Daily News article did not know that West Texas does have earthquakes. After all, the seismograph stations operating near El Paso record small earthquakes with magnitude of 2 or less every few days. Nearly every year earthquakes large enough to be felt by ordinary citizens occur somewhere in Texas. In the last part of this book, we present details about more than one hundred earthquakes that have affected Texans. Recently, in response to encouragement by the Federal Emergency Management Agency (FEMA), the Texas Division of Emergency Management asked us to evaluate earthquake hazard in Texas (Frohlich, Davis, and Pulliam 2000). We identiﬁed four geographic regions in Texas (ﬁgure 2.2) where earthquakes have occurred with some regularity in historic times and are likely to occur again. Ranked in decreasing order with respect to hazard, these are: West Texas (largest urban area El Paso); Panhandle (Amarillo); Northeast Texas (Dallas–Fort Worth); and South-Central Texas (Houston–San Antonio). West Texas (El Paso) In Texas the region with the most earthquakes, the largest earthquakes, and the greatest earthquake hazard is West Texas. El Paso, with an urban-area population of about 680,000 people, experiences more earthquakes and faces greater earth18

T E X A S E A RT H Q UA K E S

Figure 2.2. Four geographic regions in Texas that have experienced earthquakes in historic times. Symbols indicate whether earthquakes are of natural, man-made, or uncertain origin. Question marks indicate locations of questionable earthquakes, that is, events in 1873, 1887, 1907, 1914, 1925, 1950, and 1952 that were reported as earthquakes but for which the data are too sparse for the authors to conclude with certainty whether an earthquake occurred. Figure is modified from Frohlich and others (2000).

quake risk than any other Texas city. Newspaper reports indicate that El Paso residents were shaken by nearby earthquakes in 1889, 1923, 1931, 1936, 1937, 1969, and 1972. Of these, the 1889, 1931, 1936, and 1937 quakes were felt only in the city of El Paso. Except for the 1969 and 1972 earthquakes, these events are known mostly from felt reports, so we don’t have accurate locations for them. However, the 1969 and 1972 quakes were recorded clearly by seismographs; this permitted accurate locations to be obtained, conﬁrming that they had locations in or near El Paso. The largest of the El Paso earthquakes, with a magnitude of about 4.7, occurred on 7 March 1923 and was felt throughout a wide area in Texas, Mexico, EARTHQUAKES IN TEXAS

19

Figure 2.3. Locations of major structural features of West Texas. Solid lines denote faults used in U.S. Geological Survey hazard analysis, faults described in text, or other selected features of note. Circles are earthquake locations. Abbreviations: MF—Mayfield Fault; MRF—Miller Ranch section of Mayfield Fault; and RRF—Rim Rock Fault.

and New Mexico. This event has the dubious distinction of being the only Texas earthquake ever to cause a fatality, as it caused an adobe house to collapse in Mexico ten kilometers from Juarez, killing Juan Ortiz, a tenant farmer. It is possible that these earthquakes occurred along faults that have been mapped just east of El Paso which exhibit geologically recent offsets (Muehlberger, Belcher, and Goetz 1978; Seager 1980). These faults, associated with the Hueco Bolson, represent a southern extension of the Rio Grande rift (ﬁgure 2.3), which is a parallel series of geological basins extending from New Mexico into West Texas. Most of the larger earthquakes occurring in New Mexico are found along the Rio Grande rift, especially along the segment between Socorro and Albuquerque. Texas’ largest earthquake—larger even than the 1995 event— occurred on

20

T E X A S E A RT H Q UA K E S

16 August 1931 near Valentine, a small town more than 200 km southeast of El Paso. It had a magnitude of about 6.0 and was severe enough to be felt by Texans as far away as Dallas (ﬁgure 2.4), where newspapers said it was “quite appreciable,” especially in tall buildings. This was the most damaging Texas earthquake. In Valentine, Neumann (1932) wrote: all but frame houses were badly damaged, and all brick chimneys toppled over . . . The schoolhouse, consisting of one section built of cement blocks and another of brick . . . required practically complete rebuilding.

No lives were lost in this earthquake, possibly because during the preceding night there were several foreshocks severe enough to frighten people, and thus, Neumann wrote, “nearly everyone was sleeping outdoors.” Valentine, where this quake occurred, and Alpine, the town closest to the epicenter of the 1995 quake, are small towns situated in sparsely populated regions. The Valentine and Alpine earthquakes would have been much more damaging had they occurred in places with higher population densities. Both were accompanied by numerous aftershocks. There has been much speculation concerning which fault is responsible for the 1931 Valentine earthquake. The most popular choice is the Mayﬁeld Fault (Muehlberger, Belcher, and Goetz 1978; Gordon 1983; Doser 1987). This fault lies just west of Valentine and has a continuous fault scarp with a length of 80 km, the longest in this area. There have been reports of recurrent movement on the Mayﬁeld fault near the Miller Ranch, west-southwest of Valentine. Other possible candidates are the Rim Rock Fault, a major geologic feature that forms one boundary between the Diablo Plateau and the Valentine Fault, a relatively small fault situated just north of Valentine (Dumas, Dorman, and Latham 1980). Unfortunately, no search for fault displacement was made in the Valentine area after the shock. In any case, abundant evidence conﬁrms ongoing ground movement in West Texas. Geodetic surveys indicate that the Diablo Plateau is currently uplifting at a rate of about 4 mm/year, possibly due either to crustal magmatic intrusions or to preseismic deformation (Brown, Reilinger, and Hagstrum 1978; Reilinger, Brown, and Powers 1980). Surveys also show subsidence of about 11 cm (4 inches) in a zone about 20 to 30 km long near Valentine, possibly generated by the 1931 Valentine earthquake (Ni, Reilinger, and Brown 1981). The 1995 Alpine earthquake occurred near the boundary of the West Texas

EARTHQUAKES IN TEXAS

21

Figure 2.4. Felt area map for the 16 August 1931 Valentine earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Map and isoseismals are redrawn from Davis, Pennington, and Carlson (1989), who revised previous maps of Neumann (1932), Sellards (1933b), and Docekal (1970).

basins and the Marathon Uplift. Numerous geological features nearby might have generated the earthquake; these include a long north-trending escarpment to the east and southeast of Alpine, small faults mapped slightly farther east, and faults associated with the boundary of the Marathon Uplift (Ewing 1991). In fact, much of southwestern Texas is crossed by geologic structures similar to these

22

T E X A S E A RT H Q UA K E S

Sidebar 2.1 HOW FREQUENT ARE BIG EARTHQUAKES? Why is there concern about Texas earthquakes, given that historical events have done little damage? One reason is that the frequencies of small and large earthquakes are related in a predictable way. A rule of thumb called the Gutenberg-Richter relation states that for every 1,000 magnitude 4 earthquakes there will be approximately 100 magnitude 5 events, 10 magnitude 6 events, and one magnitude 7 event. Thus the occurrence of 2 earthquakes in Texas with magnitude near 6 in the twentieth century suggests that a magnitude 7 may occur every few hundred years or so. Like many other rules of thumb, the predictions of the Gutenberg-Richter law are not always correct. For example, transportation experts use rules of

thumb to predict the number of auto fatalities during a holiday weekend; these may be incorrect because of the influence of unpredictable factors such as weather and safety campaigns. Similarly, the predictions of the Gutenberg-Richter relation may be incorrect because of factors that scientists do not understand or have not considered. Yet in West Texas the record indicates that magnitude 6 quakes do occur, and larger earthquakes are possible. In the Panhandle, the occurrence of three earthquakes with magnitudes of five and above suggests that a magnitude six might occur every 300 years. This could be serious if it occurred near a major city.

associated with the Valentine earthquake, and many may be capable of producing earthquakes of similar size. In 1998 this caused considerable concern near the town of Sierra Blanca, Texas, at a site that had been proposed as a repository for low-level nuclear waste. Another part of West Texas where earthquakes have occurred is the Central Basin Platform, a structural ridge that separates the Delaware Basin and the Midland Basin. It is possible, although not certain, that oil and gas production may have induced these earthquakes. What is certain is that there is no evidence of movement in the recent geologic past along surface faults within the Central Basin, it is the site of numerous oil and gas ﬁelds, and earthquakes are known to occur there only since 1964. For example, on 2 January 1992 an earthquake with magnitude 4.6 occurred along the Central Basin Platform near the Texas–New Mexico boundary. There have been suggestions that petroleum production induced this earthquake; however, seismologists who analyzed it have estimated a depth of about 12 km, well below the depths tapped by wells (Sanford and others 1993; Doser and others 1992). Similarly, in 1966, 1976, 1977, and 1978, residents of Kermit, Texas, felt earthquakes. The 1966 shock, with a magnitude of 4.1, caused minor damage. Diane Doser and her colleagues at the University of Texas El Paso evaluated West Texas seismicity on a ﬁeld-by-ﬁeld basis and found that a variety of mechanisms inﬂuenced it (Doser and others 1992). In the War-Wink ﬁeld of Ward County, earthquakes occur mainly in or near regions where ﬂuid pressures are naturally high, approaching the weight of the overlying rock. Thus while there

EARTHQUAKES IN TEXAS

23

is some correlation between seismicity and petroleum production, the relationship is not unambiguous. Near Kermit the earthquakes seem to be related to production; the production methods there do involve the injection of high-pressure ﬂuids into wells to enhance petroleum recovery at neighboring wells, a procedure that sometimes induces earthquake activity (see chapter 5). Unfortunately, no records are available of the early injection history for the Kermit ﬁelds. Other ﬁelds in the region seem to be associated with small earthquakes, although in many cases the earthquake foci are at depths greater than the depths where oil is produced. Further to the east in the Midland Basin, earthquake activity since 1974 probably has been caused by petroleum production in the Cogdell ﬁeld (Sanford and others 1980; Davis 1985). The largest shock, with magnitude 4.6, occurred near Snyder, Texas, on 16 June 1978 (see ﬁgure 2.5; also Dumas 1979; Harding 1981; Davis 1985). Two independent investigations (Voss and Herrmann 1980; Harding 1981) concluded that the Snyder earthquakes occurred at shallow focal depths corresponding to the production depths of about 2 km. In the Cogdell ﬁeld, production methods include the injection of ﬂuids to enhance recovery; moreover, the reported injection pressures and volumes are sufﬁciently high to cause rock failure (i.e., earthquake activity). For these reasons, and because of the absence of seismic activity prior to 1974, we conclude that the Snyder earthquakes have a human—not a natural— origin (Davis and Pennington 1989). Texas Panhandle (Amarillo) In our Texas Division of Emergency Management study of earthquake hazard (Frohlich, Davis, and Pulliam 2000), the Texas Panhandle was the geographic region having the second highest risk level in Texas. Since 1900 there have been at least eight Panhandle earthquakes with magnitudes of 4 or greater; three of these, in 1925, 1936, and 1948, had magnitudes greater than 5. The majority of these quakes occur along the boundary between the Amarillo-Wichita Uplift and the Anadarko Basin (ﬁgure 2.6). This is a region with steeply dipping faults in the rocks beneath the uppermost sedimentary layers (Goldstein 1982). These faults extend from the Panhandle into southwestern Oklahoma, where offsets exceed 9 km on some faults (Budnik and Smith 1982). The largest and most widely felt Panhandle earthquake occurred on 30 July 1925; this had a magnitude of 5.4 and produced MMI VI intensities at a number of cities between Amarillo and Pampa, Texas. Subsequently, several scientists (Pratt 1926;

24

T E X A S E A RT H Q UA K E S

Figure 2.5. Felt areas for the 16 June 1978 Snyder and 9 June 1980 Pampa earthquakes. Pampa is the unlabeled town in MMI V region of 1980 earthquake; Skellytown is the unlabeled town 20 km to the west of Pampa; the town labeled Mob. is Mobeetie. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded regions indicate major oil (dark shading) or gas (light shading) fields, as mapped by Galloway and others (1983) and Kosters and others (1989), that were established prior to 1978. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989).

EARTHQUAKES IN TEXAS

25

Figure 2.6. Structural features of Texas. Solid lines denote faults used in U.S. Geological Survey hazard analysis, faults described in text, or other selected features of note. Circles are earthquake locations. Abbreviations: AWU—Amarillo–Wichita Uplift; BF—Balcones Fault; CJFZ— Charlotte–Jourdanton Fault Zone; CBP— Central Basin Platform; DP—Diablo Platform; MEFZ—Mount Enterprise Fault Zone; LFZ—Luling Fault Zone; OTF— Ouachita Tectonic Front.

Woollard 1958; Gordon 1983) have proposed that the 1925 earthquake might be related to the faulting within the Amarillo-Wichita Uplift–Anadarko Basin system (ﬁgure 2.6). On 20 June 1936 another quake, with magnitude of 5.0, produced intensities as high as MMI VI in Borger, Texas; on 9 June 1980 a smaller earthquake (magnitude about 4.3) occurred near Pampa. While none of these earthquakes was especially large or damaging, their association with the Amarillo-Wichita Uplift is of concern because of speculation (Braile and others 1982; McKeown 1982) that a geologically similar feature, the Reelfoot Rift, produced a sequence of three earthquakes with magnitudes of 8 or more in 1811 and 1812 near New Madrid, Missouri (ﬁgure 1.3). If the Reel-

26

T E X A S E A RT H Q UA K E S

foot Rift is not somehow unique, it is possible that similar great earthquakes might occur in Texas and central Oklahoma in the region between the Panhandle and the northern end of the Ouachita Thrust Zone (Keller and others 1983; Budnik 1987). There are also reports of geologically recent movement along the Meers Fault in Oklahoma, suggesting that this region is experiencing tectonic stress buildup (Donovan and others 1983). However, since the largest historic earthquake in the Texas Panhandle had a magnitude of only 5.4, this is mere speculation. Undoubtedly, many important questions remain about these Panhandle earthquakes. Neither the amount nor the direction of offset on the faults that produced them has been established from analysis of seismic records, and no surface fault breakage has been identiﬁed for any of them. Therefore, it is quite possible that many Panhandle earthquakes are not of natural origin but are induced by petroleum production. The highest-intensity regions of the 1925, 1936, and 1980 earthquakes coincide with the boundary of the Panhandle oil and gas ﬁeld, one of the largest oil and gas ﬁelds in Texas. Its association with seismic activity is certainly not entirely a coincidence, as the same geologic features that might cause earthquakes also have produced rather effective traps for oil and gas. And the Panhandle ﬁeld was under development well before 1920 (Galloway and others 1983; Kosters and others 1989). Controversy about a link between petroleum production and Panhandle earthquakes is nothing new; in 1926 Pratt noted: a general impression that the earthquake may have been caused by oil ﬁeld operations. No evidence [supporting this] was established . . . [and] there is no reason to suspect that the removal of oil contributed to the forces which caused the earthquake.

Coffman, von Hake, and Stover (1982) agree: Many persons thought that it [the earthquake] resulted from oil drilling but the area over which it was felt precludes any such cause. However, the drilling has brought out the fact that the region is the site of a buried mountain with slopes of 1,500 to 2,000 feet in a few miles. In spite of long burial, there seems to be activity and the earthquake is probably a renewal of activity in a region once very active.

The essence of the controversy is that while the earthquakes are somewhat larger than one would usually expect to be induced by oil ﬁeld activity, no historical record is available of seismic activity in this region prior to the estab-

EARTHQUAKES IN TEXAS

27

lishment of the Panhandle ﬁeld. A magnitude 3.9 earthquake did occur in the Panhandle on 28 March 1917. However, its location and time of occurrence are highly uncertain, and we have been unable to establish whether petroleum production had begun by 1917. Finally, there is a single report of an earthquake felt in Amarillo in April 1907; however, this report wasn’t published until 1925, and it is possible the report is spurious. The limited evidence available does suggest that Panhandle residents were unaware that earthquakes might occur there. For example, an article in the Amarillo Twice a Week Harold of 27 January 1906 states: Earthquakes have been rocking Socorro, N.M. at a terrible rate. This earthquake business is growing serious, and as [sic] to be considered in selecting a place of abode. The climate and ﬂowers of the Paciﬁc will not attract so many to that section since the seismic disturbance of San Francisco. The Panhandle of Texas has less undulations and volcanic appearances than any other section of the country that we know anything about. Those who have had or anticipated an earthquake scare cannot do better than investigate the safety of the situation in the Panhandle.

On the other hand, the absence of reported activity in the Panhandle may only reﬂect the settlement history of the region. For example, in Hutchinson and Carson counties, census records from 1880 indicate only ﬁfty residents in the two counties; by 1900 the counties still had only about eight hundred residents (U.S. Census Ofﬁce 1894; U.S. Bureau of the Census 1922). Population in the Texas Panhandle grew considerably in the century’s ﬁrst two decades, especially after oil production began. Not all the earthquakes in the Texas Panhandle are situated over the Amarillo-Wichita Uplift; several earthquakes have been reported in neighboring sedimentary basins. The largest of these, with magnitude 5.2, occurred on 12 March 1948 near Dalhart in the far northeast corner of the Panhandle. This region has no signiﬁcant oil or gas ﬁelds; thus the quake’s origin must have been natural. Similar earthquakes occur in northeastern New Mexico and southeastern Colorado along a trend that may well be a western extension of the AmarilloWichita system (King 1977; Goldstein 1982). Presumably these earthquakes, like those in Borger and New Madrid, occurred on existing faults reactivated by present-day stresses. On 15 February 1974 a magnitude 4.5 earthquake occurred near Perryton, Texas, in the Anadarko Basin near the Texas-Oklahoma border. While there are

28

T E X A S E A RT H Q UA K E S

a number of gas ﬁelds near Perryton, depth estimates for the earthquake range from 10 km to 24 km, indicating that the earthquake occurred in basement rocks far beneath the oil-bearing strata (Herrmann 1979). It is possible that the Perryton event was part of a trend of earthquakes that runs through the Anadarko Basin and includes the 1952 El Reno and the 1976 Durham earthquakes, both in Oklahoma (Gordon 1983). Finally, regional seismograph stations recorded several small earthquakes with locations in eastern Oldham County. This region is sparsely populated, and we are unaware of any felt reports. The largest of these earthquakes had a magnitude of only 3.4 and occurred on 3 April 1984. Some petroleum is produced in this region, and thus these quakes may either be induced or of natural origin (Davis 1985). Northeast Texas (Dallas–Fort Worth) In the Texas Division of Emergency Management study of earthquake hazard (Frohlich, Davis, and Pulliam 2000), northeast Texas was the geographic region in Texas having the third highest level of risk. The hazard from earthquakes occurring here is considerably lower than in West Texas or the Panhandle. However, the region is of special concern because of the concentrated population in the Dallas–Fort Worth area and because it faces potential hazard from several different kinds of earthquakes—naturally occurring earthquakes, earthquakes induced by human activity, and huge but relatively distant earthquakes that occur outside the borders of Texas. The greatest hazard in this region is from very large, distant earthquakes. For example, the highest intensities for the 1811–1812 New Madrid earthquakes were at the Missouri-Tennessee boundary, where the earthquakes produced waterfalls on the Mississippi River and actually caused the river to change its course. Although we have no historical records from Texans who felt the New Madrid quakes, the intensities must have reached at least MMI VII in northeast Texas, and in the area that is now Dallas–Fort Worth the intensity would have been approximately MMI VI (ﬁgure 2.7). Although these intensities do not level ordinary buildings, they undoubtedly would produce widespread damage. There is legitimate reason to worry about how tall buildings, highway overpasses, and dams would respond to another magnitude 8 earthquake in the New Madrid region. It is possible that earthquakes in Oklahoma, such as the quakes of 22 October 1882 and 9 April 1952, might affect northeast Texas. Fortunately,

EARTHQUAKES IN TEXAS

29

Figure 2.7. Felt areas of representative earthquakes affecting northeast Texas. Shaded regions indicate regions experiencing MMI V and greater during the earthquakes that occurred on 9 April 1932, 12 April 1934, 19 March 1957, and 28 April 1964; the surrounding lines delineate the MMI IV and MMI III felt areas. Thick solid lines and plotted Roman numerals indicate estimated intensities for the 16 December 1811 New Madrid earthquake. Information shown is revised from maps in Davis, Pennington, and Carlson (1989).

very large continental-interior earthquakes like the 1811–1812 events seem to be very rare. Northeast Texas does experience small, natural earthquakes of its own. On 12 April 1934 an earthquake with magnitude 4.2 occurred in northernmost Lamar County and was felt in all neighboring counties and in southern Oklahoma. Inexplicably, Sellards (1935) called this the Trout Switch earthquake even though we have found no town named Trout Switch on maps from either then or today. A few old maps show a “Trout Spur” on the rail line between Paris, Texas, and Hugo, Oklahoma, in the region of highest intensity. Several historical earthquakes have occurred nearby in southeastern Oklahoma, suggesting that buried active faults exist along a northern extension of the Ouachita Belt

30

T E X A S E A RT H Q UA K E S

Thrust Zone. Although the highest-intensity region for the Trout Switch earthquake includes what is today Pat Mayse Lake, and although in some cases the ﬁlling of manmade lakes and reservoirs induces earthquake activity, Pat Mayse Lake deﬁnitely did not cause the Trout Switch earthquake, since construction on Pat Mayse Dam began only in 1967. Similarly, reservoirs are not responsible for a series of earthquakes that struck the Hemphill-Pineland area of eastern Texas between April and August 1964. While the quake locations lie directly between what is now the Toledo Bend and Sam Rayburn reservoirs, two of Texas’ largest manmade lakes, the ﬁlling of Sam Rayburn Dam did not begin until 1965 and construction of Toledo Bend Dam had just begun in 1964. Moreover, the highest intensities in the felt areas coincide with neither reservoir. Thus these earthquakes are of natural origin. While a temporary seismograph station deployed in 1964 near Hemphill recorded more than seventy earthquakes with magnitudes as great as 4.4, no historical earthquakes are known in this area prior to April 1964 and none were recorded after August of that year. In contrast, petroleum production probably did induce at least two earthquake sequences in this region. On 9 April 1932, a magnitude 4.0 earthquake occurred near the towns of Wortham and Mexia, 60 km east of Waco, with a location directly within the large Mexia oil ﬁeld. This ﬁeld, discovered in 1920, taps one of at least ten producing structures in Limestone, Freestone, and Navarro counties that were formed by the northeast-trending Mexia fault system. At the time of the earthquake the Mexia and the nearby Wortham oil ﬁelds had produced 90 million barrels and 22 million barrels of oil, respectively (National Oil Scouts Association of America 1932). From intensity reports Sellards (1933a) concluded that the 1932 Mexia earthquake originated on one of the major faults of the Mexia system. While a natural origin for this event is possible, the coincidence of the earthquake location with the area of highest hydrocarbon production strongly suggests it was induced (Sellards 1933a; Yerkes and Castle 1976; Carlson 1984). Similarly, petroleum production is probably also responsible for a series of four earthquakes, the largest with magnitude 4.7, that all occurred on 19 March 1957 near Gladewater, Texas. Felt reports indicate that the epicenters were approximately between Gladewater and Longview, directly above the northern part of the East Texas oil ﬁeld in the area of the highest density of wells. The East Texas ﬁeld was, at the time of discovery in 1930, the largest ﬁeld in the Western

EARTHQUAKES IN TEXAS

31

Hemisphere. By the time of the earthquakes, more than 3.5 billion barrels of oil had been extracted from the ﬁeld (National Oil Scouts Association of America 1958). The relatively high magnitude and large felt area (45,000 km2) of the largest earthquake are difﬁcult to explain if it was induced by ﬂuid withdrawal. Moreover, it seems unlikely that a quake with magnitude as great as 4.7 would occur at the relatively shallow production depth of 1 km. Nevertheless, because of the huge volume of ﬂuid removed from the oil ﬁeld, we believe that the earthquake was induced. Its location has never been associated with any known fault. South-Central Texas (Houston–San Antonio) In the Texas Division of Emergency Management study (Frohlich, Davis, and Pulliam 2000), the fourth region in Texas that experiences earthquakes is southcentral Texas. As in northeast Texas, these include quakes with both natural and human origins. However, the events are rare and quite small, so they probably pose little or no hazard. For example, in historic times two earthquakes have been felt in Austin, one on 5 January 1887 and another on 9 October 1902 (ﬁgure 2.8). Both of these quakes had magnitudes of about 4.0. The 1902 quake was felt most strongly in southern Travis County, and because of the rarity of seismic activity, there was much consternation and some confusion about what had actually occurred. The Austin Daily Statesman reported that: There were heard two terriﬁc reports in quick succession, similar to those made by great cannons . . . There were some people in Austin who believed that Pilot Knob or Round Mountain was in a state of eruption and they got on the lookout for ﬂowing molten lava . . . It was ﬁrst thought at Dutch Water Hole that a boiler had exploded . . . It was also believed by some that the Beaumont oil ﬁelds had blown up.

The San Antonio Express reported: The mysterious explosive noise and earth trembling which occurred on Thursday about noon and was heard and felt throughout a wide section of the country was explained today by M. E. Houston, a well known farmer living on Cedar Creek. . . . He says the phenomena [sic] was caused by a meteor which exploded near Pilot Knob. Several negroes were working in the ﬁelds when they saw a mass of ﬂame sweep down towards them. When within a mile of them, the meteor burst and the concussion threw them to the ground. A search is now being made for fragments of the meteor.

32

T E X A S E A RT H Q UA K E S

Figure 2.8. Felt areas of representative earthquakes affecting south-central Texas. Shaded regions indicate regions experiencing MMI V and greater during the earthquakes that occurred on 5 January 1887, 9 October 1902, 8 May 1910, 9 April 1993, and 24 March 1997; the surrounding lines delineate the MMI IV and MMI III felt areas. Information shown is revised from maps in Davis, Pennington, and Carlson (1989), Davis, Nyffenegger, and Frohlich (1995), and Bilich and others (1998).

Neither of these earthquakes can be attributed to petroleum production, since oil was not discovered in this part of Texas until 1912. East of the Llano Uplift, the main tectonic features in central Texas are a series of fault systems that are part of the so-called Ouachita Belt, which extends from Mexico through central Texas to Oklahoma and Arkansas. These include the Balcones, the Charlotte-Jourdanton, the Luling, and the Mexia-Talco fault systems. None of these

EARTHQUAKES IN TEXAS

33

faults is presently very active; however, the 1902 earthquake appears to have occurred in the eastern part of the Balcones Fault system, while the 1887 event was in the southern part of the Mexia-Talco system. Gulfward of the Ouachita Belt, rare, small earthquakes occasionally occur in the Gulf Coastal Plain. One such earthquake, with a magnitude of about 3.8, occurred near Hempstead, Texas, on 8 May 1910. Although this earthquake was of natural origin, its precise cause is undetermined. This earthquake and similar small events that occasionally occur in southeast Texas and in Louisiana might be caused by movement within the salt domes found in several places near the surface. Within these domes the salt tends to move upward because it is less dense than surrounding sediments, and small earthquakes could occur when the accumulated strain within overlying sediment is released along faults. Another possibility is that the seismicity results as the earth’s crust adjusts to loading from ongoing sedimentation in the Gulf of Mexico. Farther to the southwest, a number of Texas earthquakes almost certainly have been caused by petroleum production. Southeast of San Antonio, since 1973 several earthquakes have occurred within the Imogene oil ﬁeld and the Fashing gas ﬁeld near the towns of Pleasanton and Fashing. The producing horizons in both ﬁelds are bounded by faults. After a 3 March 1984 Pleasanton quake scientists deployed several temporary seismographs, and analysis of the resulting data demonstrated that the events originated at or near the intersection of the fault contact (Pennington and others 1986). The largest of these earthquakes, with a magnitude of 4.3, occurred near Fashing on 9 April 1993. The intensities in the epicentral region were MMI VI, which is high for such a small earthquake; this suggests that the focal depth must have been quite shallow. The greatest damage occurred at the Warren Petroleum Plant, which processes natural gas from the Fashing gas ﬁeld; several reinforced concrete foundation blocks and a pipe connection were cracked or broken. A notable feature of this earthquake was that it attracted the attention of the Branch Davidians, a religious group that was under siege at this time by the FBI near Waco, Texas. The Davidians’ leader, David Koresh, had previously warned “of an earthquake in Waco and the presence of four angels ‘ready to punish foolish mankind’” (Washington Post 15 April 1993). United Press International reported on 12 April 1993: [FBI special agent Bob] Ricks said the Branch Davidians were “quite excited” last week about the minor earthquake that occurred about 200 miles southwest of Waco

34

T E X A S E A RT H Q UA K E S

Sidebar 2.2 SHOULD WE EXPECT DAMAGING EARTHQUAKES ON THE BALCONES FAULT? Probably not. The Balcones Fault is the boundary between the central Texas hill country to the west of Austin and the flatter plains regions to the east. About 10 million years ago this was a very active fault, but it is quite inactive nowadays. A “fault” simply represents a boundary between two sections of the earth’s crust that move or slip relative to one another. When slip is ongoing, the fault is active. After the slip stops, the fault remains. Thus in Texas and elsewhere the land is riddled with faults that no longer present any significant earthquake risk.

There are numerous examples of faults that are active but that do not have any earthquakes. Land in some communities southeast of Houston, such as at Clear Lake and Dickinson, is sinking because water has been pumped from the ground for many years; this sinking may be associated with slip along faults. However, when such slip is a slow or continuous “creep” it isn’t an earthquake, although it may cause other problems. To cause an earthquake the faults need to “stick,” then slip suddenly enough to radiate seismic waves.

Figure 2.9. Label from a bottle of Balcones Fault Red Granite Beer, brewed by the Hill Country Brewing and Bottling Company of Austin, Texas. Photo by Tom Frohlich. Used with permission.

EARTHQUAKES IN TEXAS

35

Sidebar 2.3 HOW DO WE ASSESS EARTHQUAKE HAZARD? In any particular region, the level of earthquake hazard depends on many factors. These include the size, location, and frequency of earthquakes that might occur. The amount of damage they could cause also depends on the population density, the topography, the thickness and type of soil cover, and the nature of man-made improvements In practice, the most important factor affecting scientific hazard estimation is the historical record of earthquake activity; regions that have had large earthquakes in the past will certainly experience them again. Although scientists who estimate hazard do include information about mapped faults, this information is less important than the historical record, since many known faults are not seismically active and since damaging earthquakes sometimes occur on unmapped, unknown faults. It is no accident that the regions of highest hazard in the United States Geological Survey’s

(USGS) hazard analysis correspond to the locations of known, large, historical earthquakes. In the central United States, the USGS assesses the greatest hazard in the MissouriTennessee area, where three earthquakes with magnitudes of 8 or greater occurred in 1811 and 1812. Unfortunately, the very rarity of large earthquakes makes hazard analysis an inexact science. In the twentieth century the largest earthquake in the Missouri-Tennessee area only had a magnitude of about 5.5. If the 1811–1812 quakes had occurred in New Madrid a few hundred years earlier, prior to settlement by literate peoples, would scientists know that such large and damaging earthquakes were possible there? Almost certainly not. Are we certain that earthquakes with magnitude of 7 or 8 have never and will never occur in Texas? No, we are not certain.

Sidebar 2.4 IF DRILLING FOR OIL AND GAS CAUSES EARTHQUAKES, IS IT SAFE TO CONTINUE PUMPING? Drilling itself does not cause earthquakes. However, earthquakes in some parts of Texas may be induced by the pumping of fluids at oil and gas fields or by the injection of fluids to dispose of chemical wastes. The earthquakes in the Fashing-Pleasanton area southeast of San Antonio are almost certainly caused by or triggered by pumping; such earthquakes also occur near Snyder, Texas. However, most of these earthquakes are not dangerous because

36

they usually are very small—most are tiny and occur within a few tens of meters of the injection well (Phillips and others 1998). In rare cases when injection induces larger earthquakes the magnitudes are seldom greater than about 4. Moreover, while there are tens of thousands of oil and gas wells in the state of Texas, in only a few fields does evidence indicate that oil and gas pumping induces earthquakes.

T E X A S E A RT H Q UA K E S

in south Texas, but he said they were less impressed when they found out it was so far away.

Until 24 March 1997 Texas had no known seismic activity south of the Fashing earthquakes; however, on that day a magnitude 3.8 earthquake occurred near Alice, Texas, about 60 km west of Corpus Christi. Although the origin of this event is unknown, like the Fashing events it had very high intensities over a very small area and was situated at the margin of a large oil ﬁeld, in this case the Stratton ﬁeld. Texas Earthquake Hazard How serious is the hazard in Texas from potential earthquakes? For Texans, it is important to remember three essential facts: earthquakes do occur in Texas; some are strong enough to pose a hazard; they are not as serious a threat as in some other states. First, earthquakes do occur in Texas. In the twentieth century more than one hundred earthquakes occurred that were large enough to be felt; their epicenters were in 40 of Texas’ 257 counties. Five of these earthquakes had magnitudes between 5 and 6, making them large enough to be felt over a wide area and produce signiﬁcant damage, at least locally. Second, three regions within Texas have experienced historical earthquakes strong enough to conﬁrm potential earthquake hazard. People in two regions, West Texas and the Panhandle, should expect earthquakes with magnitudes of about 5.5– 6.0 to occur every ﬁfty to one hundred years, and even larger earthquakes are possible. In northeastern Texas the greatest hazard is from very large earthquakes (magnitude 7 or above) that might occur outside of Texas, particularly in Missouri, Tennessee, or Oklahoma. In south-central Texas the hazard is generally low, but residents should be aware that small earthquakes could occur there, including some that are triggered by oil or gas production. Elsewhere in Texas, earthquakes are exceedingly rare. Outside of the four geographic regions discussed above, earthquake hazard is as low as almost anywhere in the United States. The United States Geological Survey (USGS) produces maps estimating national earthquake hazard (ﬁgure 2.10). The USGS estimates do not yet incorporate all the information presented in this book, and thus the maps underrepresent Texas earthquake hazard. However, they do indicate that only a few states have a hazard as low as that along the Texas Gulf Coast; these are North Dakota, Minnesota, Michigan, Wisconsin, Iowa, and Florida. EARTHQUAKES IN TEXAS

37

highest accelerations all correspond to the sites of known historical earthquakes. These include: Montana, 1959; West Texas, 1931; Oklahoma, 1952; Missouri-Tennessee, 1811–1812; and

Figure 2.10. Earthquake hazard map for the continental United States as prepared by the U.S. Geological Survey. In the central and eastern United States, the regions expecting the

Peak Acceleration (%g) with 10% Probability of Exceedance in 50 Years

50˚

-120

˚

10

-110˚

-100˚

-80

-90˚

2

5

2

40˚

1

4

2

2

10

10

5

4

5

3

3

2

45

Nov. 1996

10

3

30˚

4

2

1

-120

˚ -110˚

U.S. Geological Survey National Seismic Hazard Mapping Project

38

T E X A S E A RT H Q UA K E S

-100˚

-90˚

South Carolina, 1886. In many places such as Texas, the absence of detailed historical information means that earthquake hazard may be higher than indicated in this figure.

site: NEHRP B-C boundary

50˚

-70˚

0˚ 5

4

10 3

4

1

40˚

2

3

5

30˚

180 100 80 60 40 30 25 20 15 10 9 8 7 6 5 4 3 2 1 0

-70˚ -80˚

Finally, while Texas does face some earthquake hazard, this hazard is extraordinarily small in comparison to many other states, including California, Missouri, Montana, South Carolina, and Washington. In most parts of Texas there is no need to enact sweeping changes in construction practices or take other drastic measures to mitigate earthquake hazard. EARTHQUAKES IN TEXAS

39

CHAPTER 3

EARTHQUAKES IN THE UNITED STATES

The Big State Earthquake Contest As children, we played with a puzzle of the United States in which each state was a separate puzzle piece. From this, the most memorable fact many of us learned was that Alaska and Texas are the largest states, with Montana and California not too far behind; other states are not even close. Coincidentally, three of these states have had a disproportionate share of the nation’s large earthquakes. In the past eighty years Alaska, the largest state, has experienced the largest earthquake of all, the 28 March 1964 Good Friday earthquake, with a magnitude Mw of 9.2. California’s 1906 earthquake, with a magnitude MS of 8.3, was the largest outside of Alaska. The 18 August 1959 Hebgen Lake earthquake in Montana, with a magnitude of about 7.5, was the largest outside of Alaska and California. Since 1920 no other states have had earthquakes nearly as large as these, although, as we shall see, several had similarly large earthquakes earlier. Thus if we held a Big State Earthquake Contest, Texas clearly would be the loser (ﬁgure 3.1), as its largest quake, the 1931 Valentine earthquake, had a magnitude of only about 6.0. Of the nation’s ﬁfty states, about ﬁfteen have had larger earthquakes than Texas in historic times (ﬁgure 3.2). Alaska’s biggest earthquakes aren’t just big by American standards; they are among the biggest in the world. The 1964 earthquake, for example, is the second largest earthquake we know about—anywhere. This earthquake leveled buildings and caused impressive landslides in Anchorage, Alaska’s largest city, even though the epicenter was 130 km to the east. Geologically, it involved rupture along an 800 km section of the Paciﬁc–North American plate boundary; slip on this fault produced uplifts of more than 10 meters west of the epicentral area. The water displaced by these uplifts produced a tsunami that was responsible for most of the damage and the majority of the 115 fatalities. The tsunami destroyed the ports of Seward and Valdez, killed 23 of 76 inhabitants of the Aleut ﬁshing village of Chenega, and swept out across the Paciﬁc. Although the most devastating effects of the tsunami were in Alaska, it also drowned 4 people camping on the beach in Depoe, Oregon, and 10 more people at Crescent City, California, where it also demolished 150 stores and littered the streets with redwood logs from a nearby sawmill. As remarkable as this earthquake was, it was not particularly unusual for Alaska. Indeed, in one list of the ﬁfteen largest earthquakes in U.S. history (table 3.1), all nine in the twentieth century were in Alaska.1 This included the world’s third biggest earthquake in the twentieth century, which had a magnitude Mw of 40

Figure 3.1

Figure 3.2. Locations of largest known earthquakes within each state in the continental United States, as reported in Stover and Coffman (1993). Symbols indicate event magnitude. EARTHQUAKES IN THE UNITED STATES

41

Table 3.1 / THE 15 LARGEST EARTHQUAKES IN THE UNITED STATES DATE

LOCATION

MAGNITUDE*

DEATHS

28 March 1964

Prince William Sound, Alaska

9.2

125

9 March 1957

Andreanof Islands, Alaska

8.8 (9.1)

4 February 1965

Rat Islands, Alaska

8.7

10 November 1938

E. of Shumagin Islands, Alaska

8.3

10 July 1958

Lituya Bay, Alaska

8.3

10 September 1899

Yakutat Bay, Alaska

8.2

4 September 1899

Near Cape Yakataga, Alaska

8.2

7 May 1986

Andreanof Islands, Alaska

8.0

7 February 1812

New Madrid, Missouri

7.9

“several”

9 January 1857

Fort Tejon, California

7.9

1

3 April 1868

Ka’u District, Island of Hawaii

7.9

77

9 October 1900

Kodiak Island, Alaska

7.9

30 November 1987

Gulf of Alaska

7.9

26 March 1872

Owens Valley, California

7.8

24 February 1892

Imperial Valley, California

7.8

5

27

Source: Stover and Coffman (1993). *Magnitude listed is that preferred by Stover and Coffman (1993), with alternate magnitudes used elsewhere in this book in parentheses. As discussed in chapter 1, there are different magnitude scales, and for earthquakes occurring prior to about 1977 reported magnitudes are notoriously variable.

9.1 and occurred on 9 March 1957 along the Aleutian Islands in the Andreanof Islands about 2,000 km southwest of Anchorage. On 4 February 1965 another Aleutian quake, still farther to the west in the Rat Islands, had a magnitude Mw of 8.7. Indeed, the 1957, 1964, and 1965 quakes were so large that they were directly responsible for the invention of the moment magnitude, or Mw scale (see chapter 1). At the time they occurred, seismologists who carefully studied their intensities realized these quakes had fault ruptures and felt effects that were much larger than those in ordinary “great” earthquakes; however, their magnitudes under Charles Richter’s MS scale were “only” 8.1, 8.4, and 8.2, respectively. Thus, the moment magnitude Mw was developed to properly measure the sizes of both large and small earthquakes. Nowadays, if both magnitude measures are available, most seismologists prefer to use Mw rather than MS to measure earthquake size.

42

T E X A S E A RT H Q UA K E S

Table 3.2 / THE 15 LARGEST EARTHQUAKES IN THE LOWER 48 STATES DATE

LOCATION

MAGNITUDE*

DEATHS

7 February 1812

New Madrid, Missouri

7.9

“several”

9 January 1857

Fort Tejon, California

7.9

1

26 March 1872

Owens Valley, California

7.8

27

24 February 1892

Imperial Valley, California

7.8

16 December 1811

New Madrid, Missouri

7.7

“several”

18 April 1906

San Francisco, California

7.7 (8.3)

3,000

3 October 1915

Pleasant Valley, Nevada

7.7

23 January 1812

New Madrid, Missouri

7.6

28 June 1992

Landers, California

7.5

21 July 1952

Kern County, California

7.3 (7.5)

24 November 1927

West of Lompoc, California

7.3

16 December 1954

Dixie Valley, Nevada

7.3

18 August 1959

Hebgen Lake, Montana

7.3 (7.5)

28

28 October 1983

Borah Peak, Idaho

7.3

2

31 January 1922

West of Eureka, California

7.3

“several”

1

Source: Stover and Coffman (1993). *Magnitude listed is that preferred by Stover and Coffman (1993), with alternate magnitudes used elsewhere in this book in parentheses. As discussed in chapter 1, there are different magnitude scales, and for earthquakes occurring prior to about 1977, reported magnitudes are notoriously variable.

Since Alaska did not become a state until 3 January 1959, a nitpicker could argue that for most of the twentieth century, California actually was the state with the largest earthquakes. While California may have lost its claim in 1964, it certainly does experience large earthquakes; up to the present it has suffered more earthquake damage and more earthquake fatalities than any other state (see table 3.2). In historic times two California earthquakes have had magnitudes of 8 and above. The better-known was the San Francisco earthquake of 18 April 1906; with an estimated 3,000 fatalities, it has been the deadliest earthquake to occur in the United States. In 1906 San Francisco was a major commercial center, and the quake leveled numerous buildings. However, much of the damage and most of the fatalities were caused by ﬁres, aggravated by the fact that the quake had burst water mains, making ﬁreﬁghting difﬁcult. A California earthquake on 9 January 1857 near Fort Tejon, about 120 km

EARTHQUAKES IN THE UNITED STATES

43

Table 3.3 / U.S. EARTHQUAKES IN WHICH DAMAGE EXCEEDED $100 MILLION, as Corrected for Inflation to Year 2000 DAMAGE; CORRECTED FOR INFLATION TO YEAR 2000

LOCATION

$400,000,000

$7,700,000,000

San Francisco, CA

1933 March 11

$40,000,000

$540,000,000

Long Beach, CA

1935 October 19

$19,000,000

$240,000,000

Helena, MT

1946 April 1

$25,000,000

$230,000,000

Alaska

1949 April 13

$25,000,000

$180,000,000

Seattle, WA

1964 March 28

$540,000,000

$3,000,000,000

Alaska

1971 February 9

$553,000,000

$2,400,000,000

San Fernando, CA

1987 October 1

$358,000,000

$530,000,000

$5,600,000,000

$7,600,000,000

1992 June 28

$92,000,000

$110,000,000

1994 January 17

$15,000,000

$17,500,000,000

$1,000,000,000

$960,000,000

DATE

1906 April 18

1989 October 18

2001 February 28

DAMAGE; VALUE IN YEAR OF OCCURRENCE

Whittier, CA Loma Prieta, CA Landers, CA Northridge, CA Tacoma-Seattle, CA

Source: Dunbar and others (1992), updated with estimates of insured losses for more recent quakes; damage in dollars for year 2000 calculated using U.S. Bureau of Labor Statistics consumer price index for all urban consumers.

northwest of what today is Los Angeles, was larger and more severe than the 1906 quake. Near Tejon the quake threw down trees and buildings, and an oval corral was converted by horizontal dislocation of the ground into an open S-shaped ﬁgure. At Ventura the roof of the mission church collapsed. The quake caused only one fatality, when an adobe house fell. Because of the sparse population in the area in 1857, this quake caused little damage. Were it to occur now, though, it would be the most destructive California earthquake since Europeans settled in California in the eighteenth century (Wood 1955; Allen 1925). As noted in sidebar 2.1, “How Frequent Are Big Earthquakes?” in the previous chapter, in places where magnitude 8 earthquakes occur every century or two, we may expect magnitude 7 quakes every ten to twenty years. This certainly seems to be true in California. In the twentieth century the most signiﬁcant earthquakes with magnitudes greater than 7 were: the Imperial Valley earthquake of 19 May 1940 (magnitude MS 7.1), the Kern County earthquake of 21 July 1952 (magnitude Mw 7.5), the Loma Prieta earthquake of 18 October 1989 (magnitude Mw 7.1), the Landers earthquake of 28 June 1992 (magnitude Mw 7.3), and the Hector Mine earthquake of 16 October 1999 (magnitude Mw 7.2). 44

T E X A S E A RT H Q UA K E S

Sidebar 3.1 IS IT SAFE TO MOVE TO CALIFORNIA? Considering the risk from earthquakes, is it safe to move to California? Or, because of the 1989, 1992, and 1999 earthquakes, can we say that the “pressure is off” and that California will not have any bad earthquakes for many years? California can be safe, but as is true anywhere, you need to exercise some common sense about where you live and work. Before finding a home in California you might want to find out where the known active faults are and avoid living in poorly constructed stone buildings or in structures situated on steep slopes. But is the pressure off? For several reasons, the answer is “No.” First, of the 1989, the 1992, or the 1999 quakes, with magnitudes of about 7, none was the “Big One,” which would have a magnitude of 8 or so. And even if a magnitude 8 does occur in California, it does not necessarily reduce the chances that another

big quake could occur. For example, in 1811– 1812 when the New Madrid earthquakes occurred, three shocks, each with a magnitude near 8, struck in a three-month period. There is controversy nowadays among seismologists about the nature of the “earthquake cycle.” Part of the controversy is about whether earthquakes have a cycle at all. If they do have a cycle, a big earthquake should reduce stress for some time. It would then be true that “the pressure is off.” However, perhaps earthquakes are more like a “relaxation phenomenon” in which the likelihood of a big earthquake is highest just after a big earthquake occurs and then decreases gradually. Light bulbs are a familiar example of a relaxation phenomenon. All bulbs burn out eventually, but new light bulbs are more likely to burn out than bulbs that have been used for a while.

Seismologists tend to group western Nevada in the same geologic province as California. Whether the judges of the Big-States Earthquake Contest would let this pass is unclear, but certainly Nevada has had some huge earthquakes. The largest, which occurred on 3 October 1915 and had a magnitude of 7.7, was felt in Oregon, California, and Utah and produced a vertical fault scarp 5 to 15 feet high and 22 miles long. It also threw down water tanks, ﬂattened adobe houses, and caved in mine tunnels. Nevada experienced two other earthquakes almost this big, in 1932 and 1954. The public heard little about the Nevada events, however, probably because no one was killed and the state was so sparsely populated. Outside of Alaska, California, and western Nevada, the largest twentiethcentury U.S. earthquake was the 1959 Montana earthquake, with magnitude Mw of 7.5. This quake produced extensive surface faulting near Hebgen Lake, a manmade lake formed by damming the Madison River west of Yellowstone Park. It also caused a landslide that further dammed the river and created a second, natural lake now called Earthquake Lake downstream of Hebgen Dam. Unfortunately, the quake and landslide killed twenty-six people camped in an overﬂow campground beneath the slide area; it would have caused few fatalities if the earthquake had not occurred during the peak tourist season in August and if it had not occurred at night. If you are interested in earthquakes, the Hebgen Lake area is a wonderful place to visit. Numerous roadside markers describe the EARTHQUAKES IN THE UNITED STATES

45

events surrounding the 1959 earthquake; drowned tree stumps from the pre1959 forest are still visible in Earthquake Lake; and the U.S. Parks Service operates a museum where the slide occurred. One of the authors of this book speculated that the damming of the Madison River might have been one factor that contributed to triggering the Hebgen Lake earthquake (Frohlich 1998). If so, it would make it the largest earthquake known that was induced by a manmade lake or reservoir. However, other scientists (Zreda and Noller 1998) subsequently analyzed the effect of cosmic rays on bedrock along the 1959 fault scarp and concluded that the fault apparently had slipped six previous times over the past 24,000 years. A manmade origin for the 1959 earthquake now seems unlikely. The Rest of the West For reasons that are puzzling, most Americans do not think of the Paciﬁc Northwest as a region facing great earthquake hazard. To achieve the highest levels of hazard, a region must (1) be subject to large-magnitude earthquakes and (2) have a lot of people and buildings. By these criteria, Seattle and the surrounding region is the highest-hazard area in the United States, outside of California. It also faces hazard from the possible eruption of the “dormant” Mount Rainier. To a geologist, “dormant” means “has not erupted during recorded history but could erupt tomorrow or perhaps not for thousands of years.” In historic times the state of Washington experienced signiﬁcant earthquakes in 1946, 1949, 1965, and 2001. The largest, with magnitude 7.3, was the 23 June 1946 earthquake; although this was felt strongly in Seattle and Tacoma, it actually occurred in British Columbia, Canada. The 13 April 1949 Olympia earthquake had magnitude 7.0 and caused heavy property damage over a wide area of Washington and Oregon. At Olympia, Washington’s capital, water and gas mains were broken and nearly all large buildings were damaged. A half-mile section of a 100-meter cliff toppled into Puget Sound near Tacoma. The 29 April 1965 earthquake that occurred near Seattle was somewhat smaller, with a magnitude of 6.5. However, it produced MMI VII damage over a large area and small pockets of MMI VIII in Seattle and surrounding suburbs. The 28 February 2001 earthquake had a magnitude of 6.8 and an epicenter between Tacoma and Olympia. Although it produced at least a billion dollars of damage in Seattle, Tacoma, and surrounding areas, few lives were lost since the earthquake focus was unusually deep (about 50 km) and it did not occur beneath a heavily populated area.

46

T E X A S E A RT H Q UA K E S

For many years there has been a controversy among seismologists concerning the size of the maximum possible Paciﬁc Northwest earthquakes. One side argues that the largest quakes will not have magnitudes larger than about 7.5; that is, they will not be larger than the largest quakes that have occurred since about 1830, when missionaries and fur traders ﬁrst became active in the region. The other side argues that the overall geologic setting—with active coastal volcanoes adjacent to an ocean with a geologically very young ocean ﬂoor—implies that extraordinarily large earthquakes are possible, perhaps with magnitudes as large as 9. Unfortunately for Seattle, scientiﬁc evidence accumulated over the past decade favors the large-earthquake proponents. The data indicate that in prehistoric times, magnitude 9 earthquakes probably did occur in the Paciﬁc Northwest and thus are likely to occur there again. For example, for one study a scientist dug trenches in carefully selected places along the Paciﬁc coast and showed that at least two probable earthquake-related subsidence events have occurred over the past 2,000 years, most recently about 300 years ago (Atwater 1992). Circumstantial evidence (Satake and others 1996; Obermeier and Dickenson 2000) likewise suggests that a tsunami that inundated the east coast of Japan on 26 January 1700 originated from a magnitude 9 earthquake in the Paciﬁc Northwest. Just think about how devastating such an earthquake would be if it occurred nowadays, considering that the 28 February 2001 magnitude 6.8 earthquake caused more than a billion dollars’ damage. Hawaii is another state that few Americans associate with seismic activity, but in fact it has experienced extraordinarily severe earthquakes. Near Kau on the southern part of the island of Hawaii, on 2 April 1868 an earthquake with magnitude of about 8 occurred that may have produced the highest Mercalli intensities of any event in U.S. history. Near the epicenter the shaking destroyed stone buildings and threw wood-frame houses off their foundations (Wyss 1988). Straw houses with posts in the ground were torn to shreds. At two locations the ground acceleration may have exceeded the earth’s gravity, as there were reports of boulders thrown over undisturbed turf and people who “bounced like balls.” On 29 November 1975 a signiﬁcant but smaller earthquake, with magnitude 7.5, occurred near Kalapana, about 50 km to the northeast of the 1868 epicenter. Hawaiian earthquakes are different in two signiﬁcant ways from those elsewhere in the United States. First, it seems likely that they may be caused at least indirectly by volcanic activity. Over time, erupted material loads and stresses

EARTHQUAKES IN THE UNITED STATES

47

the crust from above, or the movement of magma can stress the crust from within and below. After the 1868 earthquake a ﬁssure 5 km long opened in the epicentral region, and a few days later, on 7 April, a volcanic eruption occurred. Second, Hawaiian earthquakes involve the risk of tsunamis caused either by sudden uplift of the sea ﬂoor or by huge landslides into the sea. After the 1868 earthquake a tsunami occurred along the Kau-Puna southern coast of the island of Hawaii. Survivors reported that the wave swept in over the tops of the coconut trees at a height of at least 20 meters and drowned forty-six people. After the 1975 earthquake a tsunami that reached a maximum height of 14.6 meters killed two people. In western states other than California, Nevada, Montana, Washington, and Hawaii, both the maximum size of historical earthquakes and the potential hazard are comparatively low. The only earthquake with magnitude of 7 or greater occurred on 28 October 1983 at Borah Peak, Idaho, with a magnitude Mw of 7.0; this killed two people, caused $12 million in damage, and produced a spectacular fault scarp. One area that faces signiﬁcant hazard is Salt Lake City. Although it has not experienced a severe earthquake since the Mormons arrived more than a century ago, it is situated near the potentially dangerous Wasatch Fault. Earthquakes with magnitudes in the 6.0 – 6.5 range occurred in sparsely populated areas near the Colorado-Wyoming border in 1882 and near the Utah-Idaho border in 1934. In the Yellowstone Park region of Wyoming, one magnitude 6 aftershock followed the 1959 Hebgen Lake earthquake. Earthquakes in the “East” What is a “Yankee”? If you travel abroad, you discover that in most of the world a Yankee is anyone from the United States. In the Southern states, a Yankee is anyone from the Northern states, usually meaning any state north of the one you are in. However, in the northern half of the United States, a Yankee is anyone from New England, and in New England a Yankee is from Vermont. Among seismologists there is a similar confusion about which earthquakes are in the “east.” In the lower 48 states approximately 90 percent of all recorded earthquakes occur in California and western Nevada; thus to many seismologists “eastern” seismicity means everything east of California, or at least east of the Rocky Mountains. Because historical earthquakes with magnitudes above 6 are unknown in the Dakotas, Nebraska, Kansas, Oklahoma, and eastern Texas, to some seismologists “east” means Arkansas, Missouri, and all states eastward. Finally, because some rather large earthquakes have occurred along the Atlantic 48

T E X A S E A RT H Q UA K E S

coast states, some seismologists consider the Carolinas and New England as the east. In any case, the indisputable fact is that only two or possibly three areas east of the Rocky Mountains have experienced earthquakes with magnitudes above 6 in historic times. Of course, the ﬁrst exception is the New Madrid region along the Mississippi River where the boundaries of Missouri, Arkansas, Tennessee, and Kentucky meet. As mentioned previously, between December 1811 and February 1812 this area had three extraordinary earthquakes with magnitudes of about 8. At the time a few small communities, such as New Madrid, had sprung up along the Mississippi River, the main avenue of transportation for what was then the “west” (and is now the “east”). The earthquakes caused inordinate havoc in the epicentral region as riverbanks caved in and islands disappeared or were formed. The area of strong shaking was two to three times larger than that of the 1964 Alaska earthquake and ten times larger than that of the 1906 San Francisco earthquake. The quakes were felt in many cities along the Atlantic coast, frightening people in Washington, D.C., and ringing church bells in Boston. In spite of the number and severity of these shocks, in the nearly two centuries since it occurred there have been few signiﬁcant earthquakes in the New Madrid region. The largest, on 31 October 1895, had a magnitude of about 6.0. In the twentieth century the three largest occurred in 1903, 1965, and 1968 and had magnitudes between 5.0 and 5.5. Since a network of seismograph stations was established in the New Madrid region in 1974, no earthquake with magnitude of 5 or greater has occurred (Johnston and Schweig 1996). In the twentieth century the record of seismic activity near New Madrid is similar to that in the Texas Panhandle, which has also experienced three magnitude 5 quakes. The second place in the eastern United States where a relatively large historical earthquake has occurred is Charleston, South Carolina. This had a magnitude of about 7 and struck on 1 September 1886. This quake killed about sixty people and damaged or destroyed many buildings; in Charleston an estimated 14,000 chimneys were toppled. An unusual feature was the widespread occurrence of sand craters and the ejection of sand in the epicentral area. Much of Charleston had been built on reclaimed land, and this undoubtedly added to the damage (see sidebar 4.3—“Why Is the Worst Earthquake Damage Sometimes Far Away from the Epicenter?”—in the next chapter). As in the New Madrid area, Charleston has experienced no serious earthquakes since 1886. In the twentieth century, the Charleston area had several quakes with magnitudes between 4.5 and 5.0 but none of greater magnitude. EARTHQUAKES IN THE UNITED STATES

49

The third area in the eastern United States that has experienced large earthquakes is New England. However, they mostly occurred in colonial times, making their sizes and exact epicenters subject to dispute. For example, on 18 November 1755 an earthquake was felt strongly around Boston and Cape Ann, Massachusetts. It shattered or threw down more than 1,000 chimneys and was felt from Nova Scotia to Maryland. Sailors on ships at sea thought they had run aground, and it generated a tsunami that caused minor damage as far away as the West Indies. This earthquake is loosely related to a zone of large-earthquake activity that extends eastward from the St. Lawrence Valley. Northern New York state experienced earthquakes with magnitudes between 5 and 6 in 1929 and 1944, and earthquakes with magnitudes 7 have occurred in Quebec—most recently in 1925—and off the Grand Banks of Newfoundland in 1929. Elsewhere in the east, historic earthquakes are all smaller than 6.0. Indeed, in some states, the largest known earthquakes are almost laughably small. States where the largest known earthquakes have magnitudes between 4 and 5 include Georgia, Michigan, Mississippi, Pennsylvania, Vermont, and West Virginia. In Rhode Island the largest historical earthquake occurred on 11 March 1976 and had a magnitude of about 3.5. In Maryland the largest historical earthquake occurred on 19 January 1990 and had a magnitude of only 2.5.2 So, where does Texas ﬁt into the larger picture of U.S. earthquake hazard? With two quakes in the twentieth century in West Texas with magnitudes between 5.5 and 6 and with three quakes in the Panhandle with magnitudes between 5 and 5.5, Texas is in the middle of the pack. Historically, it clearly does not have very damaging earthquakes with magnitudes of 7 or so as do states like California, Washington, Montana, Missouri, South Carolina, and Massachusetts. However, unlike states such as Maryland, Louisiana, Michigan, or South Dakota, Texas does occasionally have quakes that could be very damaging if they occurred near an urban area. The remarkable lack of seismicity along most of the Gulf Coast, coupled with a pattern of seismicity in the Panhandle that resembles the pattern in the New Madrid area, gives Texas a split personality with respect to earthquake risk. It is both a state with low earthquake risk and a state with moderate earthquake risk.

50

T E X A S E A RT H Q UA K E S

Notes 1. Reported magnitudes are often highly variable for very large earthquakes and for earthquakes that occurred prior to about 1977. Thus there is considerable disparity among lists that rank very large earthquakes. 2. This gives Maryland the distinction of being the state with the smallest largest earthquake. Incidentally, the 19 January 1990 Maryland earthquake occurred in the very school district where one of this book’s authors (Frohlich) attended high school. Strangely enough, Frohlich has never actually experienced an earthquake large enough or close enough to be felt, even though he has been employed as an earthquake seismologist for three decades.

EARTHQUAKES IN THE UNITED STATES

51

CHAPTER 4

EARTHQUAKES IN THE WORLD AND OUT OF THIS WORLD Not a Trivial Pursuit Recently we were at a party where people were playing Trivial Pursuit and someone drew the question, “Which country has the most earthquakes?” To our chagrin we got the answer wrong. We answered “Vanuatu,” a South Paciﬁc island nation (called the New Hebrides before 1980) that has experienced no fewer than 75 earthquakes with magnitude of 7 and above in the twentieth century.1 Unfortunately for us, the game card’s answer was “Japan.” Who was correct, the professional seismologists (us) or the makers of Trivial Pursuit? Like many of life’s interesting questions, the Trivial Pursuit question is not well-posed—-earthquakes are impossible to count unless you include a magnitude restriction such as “Which country has the most earthquakes with magnitudes greater than 7?” And as we will discuss in chapter 5, many countries like Japan or Vanuatu that experience very frequent and very large earthquakes are actually groups of islands situated in an ocean like the Paciﬁc. This can make counting difﬁcult because much damage is attributable to undersea quakes near the islands. Is it fair to say that a nation “has” an earthquake if it causes damage although its epicenter lies outside the nation’s borders? Better-posed questions might be, “Which country faces the greatest risk from earthquakes?” or “Which country’s citizens most often experience earthquakes with magnitude larger than 7?” Among industrialized nations Japan does face the greatest risk, as in the twentieth century it experienced more than one hundred earthquakes with magnitudes of 7 and greater. Moreover, while it has a land area smaller than California, it has 125 million citizens. This high population density compounds the risk (for example, an earthquake with magnitude MS of 8.2 occurred on 1 September 1923 and destroyed 575,000 dwellings in Tokyo and Yokohama). On the other hand, the 180,000 citizens of tropical Vanuatu, with a land area much smaller than Japan, experience large earthquakes more frequently. However, in Vanuatu earthquake risk is not especially great, as most people live or work in one-story buildings that are not severely damaged when large earthquakes occur. This chapter will not present a comprehensive summary of the seismicity and hazard for the entire earth. We assume most readers do not need to determine the relative levels of seismic risk for, say, Turkey and Chile. Instead, this chapter will summarize information about very large, very signiﬁcant, or very unusual earthquakes that have occurred outside the United States. This is partly

52

Sidebar 4.1 HOW MANY EARTHQUAKES OCCUR EACH YEAR? Over the entire earth, the number of earthquakes with magnitudes of 8 and greater is less than 1 each year. Each year approximately 10 earthquakes of magnitude 7 or greater and 100 earthquakes of magnitude 6 or greater occur (table 4.1). No matter where they occur, these earthquakes are all powerful enough that they are recorded by all or most of the world’s sensitive seismographs. Each year there are more than 1,000 earthquakes of magnitude 5 or greater, 10,000 of magnitude 4 or greater, and so forth. However, these smaller earthquakes are only recorded by seismograph

stations situated sufficiently near the epicenter; thus many such earthquakes that occur in remote areas on earth are not recorded, located, or catalogued by anyone. The fact that small earthquakes are very frequent but mostly go unrecorded makes global counts of earthquakes in the twentieth century meaningless unless the count is restricted to all earthquakes with magnitude greater than about 7. Only since about 1964 has the global seismograph network been able to record all earthquakes with magnitudes of 6 and greater.

Table 4.1 / GLOBAL RATE* OF EARTHQUAKE OCCURRENCE LARGER THAN GIVEN MAGNITUDE EARTHQUAKES / YR

MAGNITUDE M W

422

5.5

140

6.0

144

6.5

113.6

7.0

113.7

7.5

110.6

8.0

*Rate shown is mean annual value for Harvard earthquake catalog for years 1977 – 2000. Catalog is incomplete for M W 5.5.

just for your entertainment. After all, wouldn’t you like to amaze your friends with your knowledge of the biggest and baddest earthquakes of all time? 2 For more serious readers, we submit that this is not just an exercise in Trivial Pursuit. In some geographic regions earthquakes have affected and will increasingly affect the economic and political milieu. This is aggravated by the tendency for global population growth and for industrialization to be concentrated near the oceans, often in coastal and island regions such as Japan, Taiwan, the Philippines, and Indonesia, which regularly experience severe earthquakes.

EARTHQUAKES IN THE WORLD AND OUT OF THIS WORLD

53

Sidebar 4.2 ARE EARTHQUAKES BECOMING MORE FREQUENT? Probably not. Occasionally legitimate scientists debate this. The problem is that we only have data for the whole earth for about the past one hundred years, since seismographs were invented. And seismograph design changed so much between 1900 and 1960 that there may be errors in magnitude estimates for some large earthquakes. Considering the uncertainty caused by these problems, no clear evidence indicates that the rate has changed. But it is possible that when much more data are available scientists will find that global rate changes sometimes do occur. Literature published by some religious groups like the Jehovah’s Witnesses claims that earthquake activity is on the increase. The authors of this

book do not like to get involved in religious arguments; but, quite honestly, we see no scientific evidence of an increase. Earthquake rates may not be increasing, but earthquake risk surely is. Much of the earth’s population growth in the twentieth century was in earthquake-prone areas along the boundaries of the Pacific Ocean, including Japan, the Philippines, Indonesia, Mexico, and California. In these areas, earthquakes that might have hurt nobody one hundred years ago will cause great damage and loss of life when they occur in the twenty-first century. A related problem occurs because many of the world’s largest cities are along coastlines, making them vulnerable to tidal waves.

It is likely that sometime in the twenty-ﬁrst century an earthquake will occur that has a serious, damaging effect on the global economy or even on the world’s political framework. For example, consider the 20 September 1999 earthquake in Taiwan. Even though it occurred far from the most densely populated part of Taiwan and “only” had a magnitude Mw of 7.7, it temporarily affected the U.S. economy because it disrupted Taiwan’s production of semiconductors used in computer memory and in many other electronic devices. What would have happened if a much larger earthquake had struck near one of the world’s great cities, such as Tokyo, Los Angeles, or Mexico City? Very Big Earthquakes What was the biggest earthquake ever? The biggest ever recorded by seismographs occurred on 22 May 1960 in Chile. It had a magnitude Mw of 9.5 and occurred when a fault ruptured horizontally for a distance of about 1,100 km along the Paciﬁc coast of South America (ﬁgure 4.1). In some places this quake caused vertical uplifts as large as 6 meters. The second biggest earthquake, with a magnitude of 9.2, occurred in Alaska on 28 March 1964; it had a rupture length of 800 km and caused as much as 11 meters of uplift. Theoretical calculations suggest that the 1960 Chile and 1964 Alaska earthquakes are just about as large as possible for planet Earth. Suppose a hypothetical earthquake ruptures the entire 100 km thickness of the rigid tectonic plate and suppose this rupture extends along a fault with a length of 1,000 km and 54

T E X A S E A RT H Q UA K E S

Figure 4.1. Areas experiencing subsidence (dark shading) and uplift (light shading) associated with the Chile earthquake of 1960 (top) and the Alaskan earthquake of 1964 (bottom). The subsidence/uplift area coincides approximately with the zone of fault rupture during the earthquake. For these earthquakes, the world’s largest in the twentieth century, with magnitudes of about 9, the rupture zones are about 1,000 km in length. For a magnitude 2.5 earthquake the rupture zone is about the size of a supermarket parking lot.

EARTHQUAKES IN THE WORLD AND OUT OF THIS WORLD

55

with an average slip of 10 meters. If we calculate the scalar moment of this earthquake as described in chapter 1 and convert the moment to magnitude as in table 1.2, we ﬁnd that this hypothetical earthquake has a magnitude of about 9.3, that is, about the same as the 1964 Alaska and 1960 Chile earthquakes. Larger earthquakes would have to rupture even longer faults with an even greater average slip. Apparently, this just doesn’t happen. Indeed, the distance from the North Pole to the equator is “only” 10,000 km.3 It is difﬁcult to imagine a terrestrial source of stress that would rupture the earth’s crust over a signiﬁcant fraction of this distance. What about very large earthquakes that occurred prior to the invention of the seismograph? For several reasons, our knowledge of such events is uncertain and very incomplete. In the absence of seismograms, it can be difﬁcult to determine just how large a reported earthquake really was. Some very large earthquakes occur in unpopulated areas, do little or no damage, and go unnoticed. We know that the very largest earthquakes occur in areas such as the Aleutians, Chile, and Japan where the rigid plates are moving toward one another. Many of these areas, such as the Aleutians, have only been occupied for a century or less by literate peoples; indeed, comprehensive records document earthquake activity prior to 1700 for only a small fraction of the earth. Nevertheless, there is every reason to believe that on the average, earthquakes with magnitude 9 or greater do occur somewhere on the earth once or twice per century. The quite frequent occurrence of magnitude 8 earthquakes in South America and Alaska suggests that the 1960 Chile and 1964 Alaska earthquakes are not isolated incidents. However, only rarely can we determine the time and magnitude of pre-1900 earthquakes, as this requires a combination of historical records that prove a very large earthquake did occur and geologic proof that it caused uplift or subsidence over a very large geographic area. An example of this is the recent assertion that the tsunami that struck Japan on 26 January 1700 originated from a rare, very large earthquake in what is now Oregon and Washington. Computational modeling to evaluate the implications of contemporary Japanese accounts suggests the wave originated from the Paciﬁc Northwest, and isotopic dating of drowned tree stumps in Oregon and Washington indicates that fault movement over a suitably widespread area occurred there about three hundred years ago. But are measures such as magnitude or scalar moment the right ways to determine which earthquake is biggest? One might argue that the biggest quake

56

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was that which was felt by humans at the greatest distance. Even this is imprecise. To paraphrase a recent U.S. president-—What do you mean by “felt?” Very large earthquakes in island or coastal regions commonly produce tsunamis that travel extraordinary distances. On Hawaiian coasts, for example, earthquakes in Alaska in 1946, 1957, and 1964 produced tsunami waves that inundated some coastal areas to depths of 4 meters or greater (Lander and Lockridge 1989). The 22 May 1960 Chile earthquake produced a tsunami that caused destruction over the entire Paciﬁc Basin. In Japan, 16,000 km distant from Chile and almost halfway around the world, 199 people were killed a full day after the earthquake occurred when the tsunami arrived. The most common, direct sensations felt at great distances from large earthquakes are slow, swaying motions. These motions can make chandeliers or hanging objects swing, allow people in tall buildings to sense vague, queasy feelings, and cause sloshing in swimming pools or harbors. Sloshing produced by surface waves from the 1964 Alaska earthquake sank boats in several bayous in Louisiana, 5,000 km from the epicenter. A magnitude 8.3 earthquake on 9 June 1994 in Bolivia was sensed by people in multistory buildings in Toronto, Ontario; Minneapolis, Minnesota; and Renton, Washington, at distances of 6,500 km, 7,000 km, and 8,700 km, respectively (ﬁgure 4.2, and see Anderson, Savage, and Quaas 1995). This earthquake had a focal depth of 650 km, making it the largest earthquake with such a great depth that has occurred in the twentieth century. Very Bad Earthquakes What is bad? Clearly, being big doesn’t necessarily make an earthquake bad (ﬁgure 4.3). When the above-mentioned 9 June 1994 Bolivia earthquake occurred, it was the largest that the world had experienced since 1977. Yet even though it occurred on land and was felt over the entire continent of South America, it apparently caused remarkably little damage and few or no fatalities,4 other than breaking numerous windows in La Paz. Presumably, damage was light partly because this quake’s focal depth was unusually deep and partly because large earthquakes are so common in Bolivia and neighboring Andean nations that people are prepared for their occurrence. Other recent very large earthquakes caused little or no damage simply because they occurred in very remote areas. For example, both the Balleny Islands earthquake of 25 March 1998 (Mw 8.1) and the Macquarie Ridge earthquake of 23 May 1989 (Mw 8.1) occurred in uninhabited regions between New Zealand and Antarctica and caused no damage.

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Figure 4.2. The largest very deep earthquake known, with a magnitude MW of 8.3, occurred beneath Bolivia on 9 June 1994 at a depth of 650 km. The seismic body waves from this quake were felt by humans at greater distances than any other earthquake known. Filled circles indicate cities in North America where the earthquake was felt. Plus symbols indicate points where strong P waves are expected to arrive at the surface for an earthquake of this type. Apparently the quake was felt in the northern United States and in Canada at distances between 6,000 km and 9,000 km (dashed lines) partly because it was so deep and partly because its type allowed strong P waves to surface there.

Clearly, people are what makes an earthquake bad—when lots of people are killed or injured (table 4.2). The 27 July 1976 earthquake in Tangshan, China, (MS 7.9) caused the greatest number of deaths of any recent quake known. Tangshan had a pre-quake population of about a million people; the main industry was mining. Most of the structures in Tangshan were multiple-story, unreinforced brick and concrete buildings that collapsed during the quake. Early in 58

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EARTHQUAKES IN THE WORLD AND OUT OF THIS WORLD 59

Figure 4.3. Very large twentieth-century earthquakes. Circles indicate quakes with magnitudes (Mw, MS, or mB ) of 8 or greater occurring between 1900 and 1999 as listed in the Abe (1981) and Harvard CMT earthquake catalogs. Labels with dates indicate locations of significant earthquakes mentioned in the text. The map also shows the boundaries of the principal tectonic plates.

Table 4.2 / TWENTIETH-CENTURY EARTHQUAKES RESULTING IN ESTIMATED DEATHS EXCEEDING 100,000 DATE

LOCATION

ESTIMATED DEATHS

1908 December 28

Italy, Messina

58,000 –110,000

1920 December 16

China, Gansu and Shanxi Provinces

100,000 –200,000

1923 September 1

Japan, Tokyo, Yokohama

99,000 –143,000

1927 May 22

China, Qinghai Province

200,000

1976 July 27

China, Tangshan

242,000

Source: National Geophysical Data Center A (1992).

1977 the death toll was reported to be 655,000; however, subsequently the New China News Agency reported the ofﬁcial death toll as 242,000. Estimates of loss of life from the worst earthquake disasters are very unreliable; understandably, when tens of thousands of people are dead and most buildings are in ruins, there are more important things to do than to count bodies. However, in about ﬁve quakes in the twentieth century reports of lives lost exceeded 100,000. Most experts agree that the most deadly earthquake in historical times occurred in Shanxi Province, China, in 1556; about 830,000 lives were lost. The two principal factors affecting damage are: degree of isolation (How far is the epicenter from major cities?) and type of construction (Are the buildings easily damaged?). Thus, often relatively small but deadly earthquakes occur in regions of dense population where buildings are of unreinforced adobe, stone, or concrete; these structures fall easily and crush inhabitants. An example is the Managua, Nicaragua, earthquake of 23 December 1972; it had a magnitude MS of only 6.2, but it killed about 6,000 people.5 An old seismology saying is, “Earthquakes don’t kill people. Buildings kill people.” A large earthquake in the tropics might shake down every grass hut within 500 km. But afterwards, the people simply re-thatch their homes and go on with their lives (ﬁgure 4.4). Turning the millennium mark has stimulated the publication of numerous lists of the most signiﬁcant events of the past 1,000 years; in this vein, what was the most signiﬁcant earthquake? This is a hard question because those most affected have their own ideas about what is signiﬁcant. We can well imagine what quakes the residents of Tangshan, China, or Managua, Nicaragua, would choose, and most U.S. citizens would probably choose the 18 April 1906 earthquake in San Francisco. However, a better candidate in some ways is probably the Lisbon, Portugal, earthquake that occurred on the morning of 1 November 1755. This quake and 60

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Figure 4.4

a subsequent tsunami caused extensive damage and great loss of life in Lisbon and throughout western Europe. The ﬁrst day of November is All Saints Day, an important religious holiday, and many of the quake’s casualties occurred when churches collapsed on people attending High Mass. The quake stimulated a great deal of scientiﬁc and philosophical writing, as Europe’s greatest thinkers struggled to understand why a good and all-powerful God would allow this to happen. Perhaps the most enduring literature of this ilk was Voltaire’s celebrated satirical novel Candide, which includes a chapter in which the hero, Candide, arrives in Lisbon after barely surviving a shipwreck, just in time to experience the earthquake and tsunami that subsequently kill 30,000 inhabitants of Lisbon. In the twentieth century Candide has been rewritten as an opera, with music by Leonard Bernstein, and as the comically pornographic novel Candy by Terry Southern and Mason Hoffenberg. Is There “Life” on the Moon and Planets? “Life” for an earthquake scientist means seismic activity— evidence that stresses on or from within the Moon or planets are strong enough to cause quakes. On the Moon quakes do occur, but scientists call them moonquakes inEARTHQUAKES IN THE WORLD AND OUT OF THIS WORLD

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Sidebar 4.3 WHY IS THE WORST EARTHQUAKE DAMAGE SOMETIMES FAR AWAY FROM THE EPICENTER? On the morning of 19 September 1985 an earthquake with magnitude 8.0 occurred on the Pacific Coast of Mexico. The earthquake and an accompanying 2-meter tsunami caused some damage in the epicentral area at a few tourist resorts and industrial estates. However, the most serious damage occurred some 350 km away in Mexico City, where hundreds of buildings collapsed, about 10,000 people were killed, and there was $5 billion in property damage. Why was the damage worst so far away from the epicenter? Damage to structures depends both on the type of construction and on the properties of the material that anchors the foundation. Experience from many earthquakes teaches us that shaking intensity is amplified for structures built on loosely consolidated sediments. Thus the worst damage often occurs when cities are built on dried-up lake beds. When the Aztecs settled in what is now Mexico City in 1325 they chose a low-lying island in the western shallows of a lake because it was easy to defend. When the Spanish took the city in 1521 they chose to drain the lake, and today about half of Mexico City occupies the area of the drained lake. In

1985 the earthquake caused little damage in buildings situated on hard rock south of Mexico City, even though earthquake waves travel through hard rock with little loss of energy. But within the city the lake bed subsoils had just the right depth and mechanical properties to trap earthquake energy and destroy buildings with six or more floors. Another earthquake-prone city built on a former lakebed is Managua, Nicaragua, where 6,000 people died in an earthquake in 1972. Elsewhere, unusually severe earthquake damage often occurs when humans build structures on reclaimed land. In many coastal cities when land becomes scarce people manufacture new land by filling in shallow areas near the coast with loose earth and gravel. In the 1989 Loma Prieta earthquake, the worst damage took place in the Marina District of San Francisco, which early this century had been built on land reclaimed from the sea.6 Many of the world’s great coastal cities now are built largely on reclaimed land; in the twentieth century this intensified the damage from earthquakes for several cities, including Kobe and Tokyo in Japan.

stead of earthquakes (ﬁgure 4.5). The Apollo space missions that visited the Moon after 1969 installed ﬁve seismographs, and four of these successfully recorded seismic activity until 1977. Unlike the earth, the Moon does not have tectonic plates. However, it does have regular, shallow quakes caused by the heating and cooling of its surface. Regular moonquakes occur at depths of approximately 700 –1,200 km beneath the Moon’s surface caused by the earth’s tidal forces. Just as the gravitational pull of the Moon creates terrestrial ocean tides, the much more massive earth creates strong tidal forces on the Moon (Nakamura, Latham, and Dorman 1982). Elsewhere in our solar system, the situation is not so clear. The Viking space mission placed a seismometer on Mars in 1976 that operated for more than ﬁve months. It recorded several impulsive signals that might have been marsquakes; it is probable that these signals were not quakes, however, but rather were caused by winds buffeting the Viking’s landing apparatus.7 62

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Figure 4.5. The world’s leading authority on moonquakes is Yosio Nakamura, who has been a researcher at the University of Texas at Austin since 1972. The instrument at left is identical to one of the lunar seismographs. Photo by Cliff Frohlich.

Some of the surface features observed on radar pictures of Venus and pictures of Io and Europa, two of Jupiter’s moons, suggest that seismic activity might occur on them. Jupiter’s enormous mass must create tidal forces on its moons that exceed the forces that create moonquakes on the earth’s moon. But for now we have no seismographs in place to be sure. Notes 1. The statistic reported is for earthquakes between 13 S and 21 S, 166 E and 171 E with magnitudes MS, mB, or MW of 7.0 or greater in the catalogs of Abe (1981) or the Harvard Centroid Moment Tensor (CMT) catalog. 2. Incidentally, the 2001 edition of the Guinness Book of World Records has only four entries concerning earthquakes. 3. Actually, it is exactly 10,000 km from the earth’s pole to the equator, because the meter was initially deﬁned as 1/10,000,000 of that distance. 4. It has been difﬁcult to establish whether this quake killed any people. News media reported no fatalities. However, we subsequently came across a rather obscure publication by Cabre and Vega (1995) that notes, “In the south of Peru some people died because of landslides” caused by this quake. This fact did not appear in any of the news reports, and we have been unable to conﬁrm it. The pertinent Bulletin of the International Seismological Centre, published about two years after the quake, notes “unconﬁrmed reports of ﬁve people killed in Peru: three in Ariquipa Province by EARTHQUAKES IN THE WORLD AND OUT OF THIS WORLD

63

a landslide collapsing their house, and two in Cuzco province, one by falling debris and another by a heart attack.” 5. One indirect casualty of this earthquake was the baseball star Roberto Clemente, now in the Hall of Fame, who died in a plane crash as he ﬂew accompanying relief supplies to earthquake survivors. 6. The area that is now the Marina District was originally a tidal marsh. Much of the material used as ﬁll was rubble from the 1906 earthquake. An enormous amount of brick, rocks, and mortar needed to be disposed of, and this was just a convenient place to put it. Subsequently, as San Francisco grew the Marina District became developed, particularly in 1915 when it was chosen as the location for the Panama–Paciﬁc International Exposition to celebrate the opening of the Panama Canal. 7. After the Apollo missions ended, several noted and highly inﬂuential geophysicists published an article summarizing the results of the Viking mission in a respected research journal (see Anderson and others 1977). This article does not explicitly state that the Viking seismometer did not record any marsquakes. Nevertheless, our discussions with the knowledgeable members of the seismology community indicate that the surface emplacement of the Viking seismometer made it a very low-gain instrument that measured mostly wind-generated phenomena and that it is unlikely any of the recorded signals were of seismic origin. Our somewhat cynical view of this published article can be summarized by stating that if we were scientists involved in promoting a multibilliondollar program to send a seismometer to another planet, we might well ﬁnd it impolitic to state baldly that we measured no seismic activity. In defense of the authors of the published article, they had little control over the design decisions that placed the Viking seismometer on the surface instead of some distance underground, where it might have been able to measure seismic activity.

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CHAPTER 5

CAUSES OF EARTHQUAKES When one of this book’s authors (Davis) received his Ph.D. in seismology, a fellow student named Guillaume Cambois brought a bottle of champagne to the celebration party. When it came time to open the bottle, he asked, “Should I open it the French way or the American way?” Since Guillaume was from France, since we didn’t know what the French way was, and since this wasn’t the ﬁrst bottle opened at the party, we answered “the French way.” Guillaume removed the wire from the cork and asked for a large, heavy kitchen knife. He then turned the bottle on its side, carefully pointing it away from partygoers toward a corner, and methodically slid the backside of the knife up the side of the bottle until it hit the glass lip on the bottle just below the cork. To our amazement, the top half-inch or so of the bottle broke off cleanly just below the lip and the cork ﬂew into the corner, leaving an intact ring of glass surrounding the cork and the bottle ready for pouring. If you try this at home, try it outside so that no one gets hurt by ﬂying glass, and be sure not to point the bottle at people.1 This “champagne trick,” as we now call it, illustrates several features in common with an earthquake. The clean fracture across the neck of the bottle corresponds to the fracture of rock along a fault surface during an earthquake. For fracture to occur there must be: • a pre-existing source of stress—this is the cork and the high-pressure gas act-

ing on the glass in the neck of the bottle; • a trigger—this is the backside of the knife as it contacts the lip and momentarily exerts a localized, higher stress on the glass; • a structural weakness—the sharp corner at the lip of the bottle that concentrates the stress along a zone of weakness; • a sudden rupture—as the neck of the bottle breaks and the tiny “earthquake” occurs. The suddenness of rock fracture is an important feature of an earthquake. Any solid material—a pencil, an ice cube, or a rock—will break or deform if you squeeze it or stretch it enough. However, if rock deforms very slowly over hundreds or thousands of years by creeping or ﬂowing, nobody may care or even notice. If it breaks slowly over days or a few years, it may cause trouble that is expensive but not dangerous, like cracks in your sidewalk or the settling of your home’s foundation. But if it breaks in an instant, the sudden motion and the elastic wave that travels away from the breaking point are what we know as an earthquake. As with the champagne trick, this can hurt people if they are in the wrong place. 65

Figure 5.1. The party trick of opening a bottle of sparkling wine with a heavy kitchen knife shares many features in common with an earthquake. For either to occur, there must be a source of stress, a geometry that concentrates the stress, and a trigger. With the “champagne trick,” the gas pressure and the cork wedged in the bottle neck provide the stress, the glass lip just beneath the cork concentrates the stress, and the knife provides the trigger. After the “champagne earthquake” occurs the bottle has broken along a “fault” just beneath the lip, leaving an intact ring of glass around the expelled cork.

Natural Earthquakes and Plate Tectonics What natural processes cause earthquakes? The majority of earthquakes occur at the edges of huge, continent-size “tectonic plates” (see ﬁgure 4.3). These plates move around at speeds of several cm/year or so.2 As their edges slip by one another or move together or apart, the difference in motion creates the stresses that cause most earthquakes. If the plates are moving constantly, why don’t we have earthquakes constantly? Some of the motion occurs as gentle creeping or sliding, without any earthquakes. At other times the plate edges stick to one another and the plates store elastic energy as they continue moving. When the stuck part suddenly comes unstuck, you have an earthquake. When the stuck regions are small and 66

T E X A S E A RT H Q UA K E S

have been stuck for a few minutes or a few days, you have tiny earthquakes, so small that nobody notices, even though they occur constantly. If the stuck region is large and has been stuck for decades or centuries, you have a large earthquake. If people are hurt or property is damaged, you read about it in the papers. Of course, attributing earthquakes to plate motion avoids the real question— what causes these plates to move? In the earth’s interior, a thermal process called convection causes the rock beneath the plates to deform or ﬂow, and this ﬂow carries along the plates above. What is convection? When a material is heated from beneath, this heating causes the warmer bottom material to rise while the cooler material at the top sinks. Convection is just the technical name that describes this whole process of heating, rising, and sinking. You are probably more familiar with convection in water or air; however, it also occurs within the earth’s interior. Heated, solid rock expands, becomes less dense, and moves upward. At the surface it cools, contracts, and then—perhaps tens of millions of years later—it sinks downward back into the earth’s interior. And just as in a pot of soup or a thunderstorm, the whole motion gets organized into big rolls of up-, down-, and sideways-moving material. In the earth this sideways moving material is the plates, and it is the convective rolls beneath which move them. How can a solid material like rock ﬂow? Lots of solids deform by ﬂowing if they are under stress; this is why glaciers can creep along at several meters a day or why a ball of Silly Putty ends up as a puddle. Solids ﬂow more easily as their temperatures get close to their melting points, which is why rock at the earth’s surface may keep its shape for millions or billions of years, while rock in the warmer interior ﬂows. However, this ﬂow is very slow, so slow that if you could watch the ﬂow in the earth’s interior, you would say it wasn’t ﬂowing at all. If the rock that forms Enchanted Rock, Texas (see Figure 5.3), which is about 100 meters from top to base, ﬂowed at the same rate, after one hundred years had passed the top would only have moved about a millimeter with respect to the base. In fact, some of the most noticeable features of the earth’s surface are actually important clues telling us where the upward and downward ﬂow takes place. For example, the deepest parts of the ocean and the deepest earthquakes occur where the cold material is sinking. These so-called deep ocean trenches usually have chains of volcanic islands nearby—the Philippines, Japan, and the Aleutians in Alaska are familiar examples. Where material ﬂows upward the ocean is unusually shallow, and there are often volcanoes or hot springs on the ocean ﬂoor. One such region extends along the middle of the Atlantic Ocean, passing through Iceland and the Azores Islands. CAUSES OF EARTHQUAKES

67

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Figure 5.2. Convection is the scientific name used when heating from below causes a liquid, gas, or solid to expand, become less dense, and rise vertically. Subsequently, it cools and sinks, so the whole process forms a continuous pattern of up- and down-going motion. Thunderstorms and boiling soup are familiar examples of con-

vection in liquids and gases. Convection of solid material within the earth is what drives plate tectonics. Mid-ocean ridges mark the location of hot rising material; at the surface it cools into plates and moves away; where it is cool and dense enough to sink, a deep-ocean trench forms.

Sidebar 5.1 DO EARTHQUAKES OCCUR AT ALL DEPTHS IN THE EARTH OR JUST NEAR THE SURFACE? Most earthquakes occur within 30 km or so of the earth’s surface. At these shallow depths the rocks are cold and brittle, allowing them to fracture suddenly when they are under sufficient stress. At greater depths the temperature is higher and stress causes the rocks to deform slowly by creep or flow, so no earthquakes occur. Generally, earthquakes do not occur if the temperature is above about 600 C. However, in a few places where tectonic plates move toward each other and one plate

dives down into the earth’s interior, cold material extends to much greater depths. Thus in Japan, the Philippines, South America, and several other places, some earthquakes occur down to depths as great as 650 km. No known earthquakes anywhere have occurred with depths greater than 700 km; this means that earthquakes occur only within the uppermost one-ninth of the distance between the surface and the earth’s center.

Other Natural Earthquakes Texas is in the middle of a tectonic plate, so how can there be earthquakes in Texas? While the majority of the world’s earthquakes do occur along plate boundaries and are directly caused by plate tectonics, many earthquakes do occur far away from any plate boundary. These include a few very large and damaging earthquakes such as the 1811–1812 New Madrid, Missouri, sequence, the 1886 earthquake in Charleston, South Carolina, and the 1959 Hebgen Lake, Montana, earthquake. Of course, the convection that drives tectonic plates can cause stress in the middle of plates—not just at their edges. So plate tectonics could be at least partly responsible for mid-plate earthquakes in Texas and elsewhere. However, several other natural processes can stress rock enough to cause earthquakes. For example, as the earth’s surface cools, over millions of years it will contract. While it is free to contract vertically, in order to contract horizontally it has to break, usually along a pre-existing weakness such as a fault. Similarly, over thousands of years sediments that pile up on the earth’s surface stress the rock underneath and may cause earthquakes. Erosion does the same thing in reverse. Removing the weight of the sediments allows the rock beneath to ex-

CAUSES OF EARTHQUAKES

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Figure 5.3. Enchanted Rock is a 100-meter-high granite batholith in central Texas that is a favorite spot for hikers, campers, and rock climbers. Photo by Cliff Frohlich.

Sidebar 5.2 DO TECTONIC PLATES FLOAT ON A SEA OF LIQUID ROCK OR MAGMA? AND DO VOLCANOES OCCUR WHEN THE MAGMA BREAKS THROUGH THE PLATE? No, and no. Although the rock in the earth’s interior is flowing, it is still ordinary, solid rock— not a liquid magma. Some solid materials—like silly putty, pitch, or ice in glaciers— can flow even though they are not liquid. The lava that erupts from volcanoes is created by thermal and chemical processes in the earth and does not originate from any vast reservoir in the interior.

For example, since water is almost everywhere on the earth’s surface, many near-surface rocks have reacted chemically with water during their formation. These chemical changes lower the rocks’ melting temperature. Thus magma is formed in regions where there is convective sinking or elsewhere when near-surface rocks are heated.

pand. It is free to expand vertically but is constrained horizontally by neighboring rock; the differential expansion produces stress and, sometimes, earthquakes. For all kinds of reasons, rock everywhere is under stress.3 It will break if the stresses exceed its strength. Earthquakes Caused by Humans Because of these pre-existing stresses, earthquakes can happen just because something changes the rock’s strength. Occasionally, this “something” is human 70

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Sidebar 5.3 PLATE TECTONICS IS JUST A THEORY, SO DOESN’T THAT MEAN IT MIGHT BE WRONG? Not really. Just because an idea is called a theory doesn’t mean that it isn’t true. An enormous amount of evidence supports “theories” like plate tectonics or the theory of evolution. Even if some of the details are wrong, that does not mean the theory is

wrong. What’s different about plate tectonics is that it is relatively new—most earth scientists have only accepted it since about 1970. So when your grandparents went to school, they didn’t learn about plate tectonics.

Figure 5.4. Gulf of Mexico earthquakes. In 1960 and in 1978, earthquakes with magnitude of about 5.0 occurred beneath the Gulf of Mexico, far from the boundary of any tectonic plate. These earthquakes may have occurred because, over time, sediments deposited by the Mississippi River became so thick and heavy that they produced enough stress to break the underlying bedrock (see Frohlich 1982). The circles show the locations of the earthquakes, and the contour lines indicate the thickness (in meters) of Mississippi Fan sediments as reported by Weimer (1989).

activity that can interact with pre-existing stresses to “trigger” an earthquake. Three human activities that commonly induce earthquake activity are injecting high-pressure ﬂuids into rock formations beneath the earth’s surface, withdrawing large amounts of ﬂuids or gas from beneath the surface, and the construction of lakes or reservoirs (Gupta 1992; Simpson 1988). CAUSES OF EARTHQUAKES

71

Earthquakes Induced by Fluid Injection

About forty years ago personnel with the U.S. Army Corps of Engineers drilled a well to a depth of 3,700 m to dispose of chemical wastes generated at the Rocky Mountain Arsenal, a military installation situated a few kilometers northwest of Denver, Colorado. Injection began in April 1962 and continued for four years, during which 625 million liters of waste were injected into the well. In itself this was not unusual; ﬂuid injection into deep rock strata is an imaginative and appropriate way of solving the waste-disposal problem for certain particularly noxious chemical products. If the strata are sufﬁciently isolated from aquifers connected to surface water, the noxious materials can be contained essentially forever. And less of the material reaches the environment than with other disposal methods in which further human handling inevitably results in some environmental contamination. However, in 1965 a geologist (Evans 1966) noted a connection between the frequency of small earthquakes and the volume and timing of injection (ﬁgure 5.5). The Army discontinued the injections in February 1966. This incident would probably be of interest only to scientists (Healy et al. 1968; Hsieh and Bredehoeft 1981; Nicholson and Wesson 1992) had not three earthquakes, each with magnitudes exceeding 5.0, occurred in 1967. These were large enough to pose a genuine hazard and produced legitimate public concern among the citizens of Denver. In addition, elsewhere in the United States executives in certain industries that routinely injected ﬂuids realized that their companies might be held liable for damage if an earthquake occurred and a jury subsequently concluded, rightly or wrongly, that an injection well was responsible. How does injection cause earthquakes? Suppose that there is injection where crustal rock is experiencing a signiﬁcant amount of tectonic stress but not enough stress to break intact rock or to cause slip on “locked” faults whose sides are pressed together by the weight of overlying rock. If the injected ﬂuids ﬁnd their way to these faults, their high injection pressures may force the sides apart, unlocking the faults and allowing them to slip and release the tectonic stress as an earthquake. Because the stresses that cause the earthquake are of tectonic origin and not caused by the injection itself, the earthquake can be large—with a greater magnitude and more energy than any process attributable solely to the injection. Thus injection-induced earthquakes are not the same phenomenon as hydrofracture, a process in which very high-pressure ﬂuids are injected into in-

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Figure 5.5. Earthquakes caused by humans. Comparison of volume of fluid injected and the number of earthquakes observed at the Rocky Mountain Arsenal near Denver, Colorado. Note that earthquakes were most frequent in 1962, 1963, and 1965, when fluid injection rates were highest; however, they continued even after injection stopped in 1966. (Reprinted from P. A. Hsieh and J. D. Bredehoeft, J. Geophys. Res. 86 [1981]: 904. Copyright ©American Geophysical Union.)

tact rocks to break them to create pathways for ﬂuid ﬂow or to monitor regional stress. In a strict sense, injection does not cause earthquakes by lubricating the fault surface; injection-induced slip takes place because the fault surfaces are forced apart, not because the ﬂuid reduces the frictional properties of the fault surface (Hubbert and Willis 1957; Hubbert and Rubey 1959). Fluid injection has actually been suggested as a means of controlling earthquake hazard. Suppose, for example, that we could inject ﬂuids along faults in California and produce many thousands of harmless magnitude 3 earthquakes that released stress and prevented a magnitude 7 or 8 quake from occurring. This would clearly be in society’s best interest since big earthquakes produce casualties and damage while little earthquakes do not. However, ﬂuid injection for earthquake control is unlikely to happen any time soon. Imagine the legal and political furor that would ensue if the government began such a program and then a magnitude 8 quake occurred.4

CAUSES OF EARTHQUAKES

73

Figure 5.6

In Texas few ﬂuid injection wells are drilled for chemical waste disposal but instead to increase the production of oil and gas. In some oil ﬁelds natural pressures within oil-producing strata are high enough to force the oil to the surface and create the familiar “gusher.” However, often considerably more oil is produced if high-pressure ﬂuids are injected into distant wells, driving the oil along the strata and up the recovery well. This practice is quite common; injection to enhance recovery has been practiced on more than 2,000 oil ﬁelds in Texas

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Sidebar 5.4 WHICH TEXAS EARTHQUAKES ARE INDUCED BY OIL OR GAS PRODUCTION? Our records indicate that altogether about 130 earthquakes with epicenters in Texas were felt by Texas residents (table 9.3). Of these, 19 had epicenters within producing oil or gas fields, and 17 more had epicenters within 3 km of a field. We have evaluated these and have concluded that 22 probably were induced by human activity. However, oil and gas fields are quite numerous in Texas, so it isn’t always correct to conclude that an earthquake is caused by petroleum production just because its epicenter

is near a producing field. About 5 percent of Texas land area lies within a major oil or gas field.6 And if you check points at 1 km intervals within Texas and calculate the distance to the nearest major oil or gas field, the median distance is only 15.5 km. One should not conclude that seismic activity is induced unless earthquakes begin only after a field starts producing and unless the pattern of felt reports suggests that the quakes occurred at relatively shallow depths within the field.

(Davis and Frohlich 1993).5 Fortunately, this has induced earthquakes in only a few cases (see table 9.3).

Earthquakes Induced by Fluid Withdrawal

In a few cases the removal of natural gas, oil, or water from underground strata appears to cause earthquakes. The largest such quakes known are a remarkable series of three MS 7.0 earthquakes that occurred in April 1976, May 1976, and March 1984 near the town of Gazli, Uzbekistan, in the former Soviet Union. Earthquakes were essentially unknown in Gazli, which means “gas” in Russian, before 1956, when natural gas was discovered there. By 1966 gas production had reached 20 billion cubic feet per year (Simpson and Lieth 1985). How could something as innocuous as removing a gas cause an earthquake? In the Gazli case, a total of more than 400 billion cubic feet of gas was removed; at atmospheric pressure this corresponds to a cube more than 2.3 km on each side. If compressed and stored as a liquid, this would occupy a cubic tank with dimensions of about 250 meters on each side. Removing this much material is bound to affect the stress along underground faults in the region, which ultimately may slip to readjust the stress. To obtain magnitude 7 earthquakes as in Gazli, however, the region must experience a considerable amount of regional tectonic stress as well (Plotnikova et al. 1996). In Texas and in most other places, earthquakes attributable to ﬂuid withdrawal are much smaller, usually with magnitudes of 4.5 or less. Removing gas, oil, or water for irrigation or human consumption normally causes no earthquakes whatsoever. In Texas a more common hazard is that ﬂuid removal causes ground subsidence. This has been especially troublesome in low-lying shoreline

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communities like Pasadena, Texas, where the subsidence makes land more vulnerable to ﬂooding during hurricanes or periods of high rainfall. Reservoir-Induced Earthquakes

The construction of the 221-meter-high Hoover Dam, creating Lake Mead in Black Canyon along the border between Arizona and Nevada, was one of the great engineering feats of the 1930s; at the time Lake Mead was the world’s largest manmade reservoir. However, although the area was considered to be a seismic and had no historical record of earthquake activity, a series of small earthquakes commenced soon after the lake began ﬁlling in 1935. During 1937 local residents felt about 100 tremors, and in 1939 a magnitude 5 earthquake occurred. Seismographs installed to monitor the activity indicated that most of the earthquakes had focal depths of 6 km or less and were concentrated along existing faults within 25 km of the lake. The earthquakes continue up to the present day; by the 1970s more than 10,000 earthquakes had been recorded, including several with magnitude of about 5. Subsequently, as more large and deep reservoirs have been constructed around the world, reservoir-induced earthquakes have become a relatively common phenomenon. Indeed, induced earthquakes with magnitude exceeding 6 have occurred near reservoirs in China, India, Greece, and along the ZambiaZimbabwe border in Africa. The largest of these, a magnitude 6.3 earthquake at Koyna in India on 10 December 1967, killed two hundred people. Earthquakes with magnitudes of 3 or greater are associated with about a quarter of all reservoirs with depths exceeding 150 meters, and some reservoirs with depths of 50 meters or less report induced seismic activity (Gupta 1992). Reservoirs can induce earthquakes by two mechanisms. First, the weight of the water alone produces stress in the rock strata beneath and adjacent to the reservoir. If faults in these strata are almost ready to fail, the additional stress may trigger an earthquake. Second, the hydrostatic pressure produced by the water can cause an earthquake by “injection.” That is, the pressure may drive water through porous material below and near the reservoir; when this reaches a “locked” fault that is already experiencing tectonic stress, it can force the sides of the fault apart and trigger an earthquake. For both mechanisms the earthquake is most likely to occur while or within a few years after water depth changes substantially. Texas has hundreds of man-made lakes, and a few earthquakes have occurred

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Table 5.1 / TEXAS EARTHQUAKES OCCURRING NEAR NEWLY CONSTRUCTED DAMS

CAUSES OF EARTHQUAKES

The table lists all earthquake sequences occurring within two years of the completion of dam construction for, and within 40km of, large reservoirs as listed by the Texas Water Development Board (1974), augmented for more recent dams by information provided by the Texas Natural Resource Conservation Commission. Note that of the listed earthquakes, only the 1966 Borger and 1983 Fashing events occurred after deliberate impoundment commenced.

77

EARTHQUAKE DATE

NEARBY TOWN

DAM NAME

DISTANCE TO DAM HEIGHT QUAKE (KM) (FT)

19 March 1957*

Gladewater

Ferrells Bridge

26

90

24 April 1964*

Hemphill

Sam Rayburn

37

120

7 September 1956

29 March 1965

Hemphill

Toledo Bend

26

112

11 May 1964

3 October 1966

20 July 1966

Borger

Sanford

32

192

11 March 1962

28 January 1965

23 July 1983

Fashing

Choke Canyon

38

116

?

1982

18 September 1985

Valley View

Ray Roberts

13

141

8 June 1982

30 June 1987

*Listed earthquake is first of several in a sequence.

CONSTRUCTION BEGAN

IMPOUNDMENT BEGAN

10 January 1955

21 August 1957

that had epicenters within 40 km of a reservoir and within two years of the completion of the dam (table 5.1). However, of these, only the 1966 Borger earthquake and the 1983 Fashing earthquake actually occurred after deliberate impoundment of water began. In both cases these events occurred in the same locations as several earthquakes did before the dams were constructed. Thus, it is unlikely that either of these earthquakes was reservoir-induced. In Texas a more likely candidate for a reservoir-induced earthquake is the magnitude mbLg3.3 event that occurred on 30 January 1986 in Coke County. The quake’s location and felt reports placed it directly beneath the E. V. Spence Reservoir, which was created by a 42-meter-high dam completed in 1969. We are unaware of any previous seismic activity in this area. What Doesn’t Cause Earthquakes, and Quakes That Aren’t Earthquakes Are earthquakes more common when the sun, moon, or planets are lined up just right? Are faults more likely to slip when gravitational forces from several astronomical bodies all pull in the same direction? The answer is “No,” although this is a plausible hypothesis that is so appealing that we hear it quite often. Since gravitational attraction depends both on mass and distance, numerous scientists have wondered if tidal forces produced by the sun’s and moon’s gravitational attraction might trigger earthquakes. The sun, which is very massive, and the moon, which is very close to the earth, have about 100,000 times more inﬂuence on the earth than any planet. Thus the sun and the moon are much better candidates for triggering earthquakes than any combination of planets. This is why the height of the ocean tides depends so strongly on the positions of the sun and moon but not the positions of the planets. However, several scientiﬁc studies have looked for evidence that solar or lunar tides trigger earthquakes and have found no statistical evidence for it. In a few very specialized situations, such as when swarms of small earthquakes occur near volcanoes, tidal forces apparently do inﬂuence seismic activity. But no inﬂuence is observed for the ordinary, damaging earthquakes that most concern us. When severe earthquakes do occur near the full moon or new moon, it is just a coincidence (Heaton 1982; Rydelek, Sacks, and Scarpa 1992; Vidale et al. 1998). Similarly, there is no evidence that “earthquake weather” is a real phenomenon or that there is any daily, weekly, or annual cycle of earthquake activity. Some investigations of earthquake catalogs have found weak seasonal, weekly, or daily variations in the frequency of earthquakes reported, but this almost cer-

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tainly occurs because seismograph stations are more sensitive and can detect smaller quakes during quieter periods. However, some events that aren’t earthquakes at all ﬁnd their way into earthquake catalogs. In many parts of the United States, the most common local events recorded by seismographs are quarry blasts. For safety reasons, these are typically set off in the late afternoon, just before quarry workers leave work for the day. In the half-century following World War II various nations including the United States, China, the Soviet Union, and France have set off nuclear explosions for both political and scientiﬁc purposes. For obvious reasons, almost all of these have been clustered in a few remote geographic locations, including Nevada, Novaya Zemlya, and Tahiti. And nearly all have occurred precisely on the hour or the half-hour; after all, if you were coordinating a team of people who were setting off a highly dangerous explosion, wouldn’t you want to make it as easy as possible for your team members to coordinate their watches? Finally, sometimes sonic booms produced by supersonic aircraft are mistakenly reported as earthquakes. On 10 February 1959, for example, newspapers in the Texas Panhandle reported a series of tremors heard and felt along a peculiar linear path extending from Roswell, New Mexico, to Higgins, Texas (ﬁgure 5.7). Other parts of the United States experienced similar blasts over the next few days that newspapers speculated might be caused by earthquakes, exploding meteors, or sonic booms. Although several Air Force bases denied that any of their jets were responsible, Convair at Fort Worth, Texas, later admitted to testing a B-58 supersonic bomber in the Panhandle at the time of the tremors. Although ofﬁcials did not reveal the ﬂight path, the linear pattern of felt reports strongly suggests that this was a series of sonic booms.

Notes 1. In our experience, people who see the champagne trick performed fall into two categories: people in one category think it is stupid and dangerous because it involves breaking a bottle and produces a ﬂying cork attached to a sharp piece of glass; people in the other category think it is the neatest trick they have ever seen and immediately run home and try it themselves. If you are in the second category, please read the following four suggestions carefully. First, ﬂying corks can cause injury, especially if they carry a ring of broken glass. So always be sure to do this outdoors and be sure that the bottle is not pointed in a direction where there are people. Second, after the trick is ﬁnished be very careful about how you grab the bottle, because sometimes there are very sharp glass edges at the top of the bottle neck where the ring has broken off. The only injuries we have

CAUSES OF EARTHQUAKES

79

Figure 5.7. Cities where people reported feeling or hearing the 10 February 1959 Panhandle event. Although this was listed in several catalogs as an earthquake, the linear pattern suggests that this event was probably a series of sonic booms occurring along the flight path of a supersonic aircraft.

ever received were when we grabbed the bottle to pour champagne, and our hands slid up the bottle neck and were cut by these sharp edges. Third, when performing the trick, use a very heavy knife, slide the knife so the ﬂat of the knife is in contact with the bottle and the blunt back edge of the knife (not the cutting edge) contacts the bottle lip. The fracture is triggered by the momentum in the knife motion and not by any kind of cutting action. And fourth, slide the knife slowly and methodically; the ﬁrst time most people try this they slide the knife way too fast, and the action just breaks a big piece out of the bottle lip. 2. Is California falling into the sea? Because the western part of California is moving northward out to sea with respect to the eastern part, most geologists would probably answer “Yes.” However, since the movement is only a few centimeters each year, in a million years it will have moved only 55 km or so. For that reason, most people would say the answer is “No.” 3. See Zoback and Zoback (1980) for a summary of stress in the continental United States. 4. Do you want to sue somebody when an earthquake occurs? For a discussion of the legal aspects of liability for induced earthquakes see Cypser and Davis (1994 and 1998).

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5. The referenced article also lists criteria for deciding whether an earthquake is injectioninduced. 6. To obtain these statistics, the authors digitized the major oil and gas ﬁelds of Texas as listed by Galloway and others (1983), Kosters and others (1989), Garrett and others (1991), and Holtz and others (1991) and performed computer calculations to determine the distribution of distances separating ﬁelds and earthquakes and between ﬁelds and points at 1 km intervals within Texas.

CAUSES OF EARTHQUAKES

81

CHAPTER 6

PREDICTING EARTHQUAKES Predicting Earthquakes Is Easy You don’t think that seismologists can predict earthquakes? Well, we are seismologists, and we “predict” that: • sometime during the twenty-ﬁrst century California will experience an

earthquake with magnitude of 7.0 or greater; and • sometime during the twenty-ﬁrst century, California will experience an earthquake with magnitude of 7.0 or greater that takes place on a Saturday. Most likely, both of these “predictions” will come true. Over the past century California has experienced approximately nine earthquakes with magnitude of 7 or greater; we presume there will be similar activity in the century to come. At the rate of nine quakes per century, the chances are better than even that at least one will occur on any particular day of the week, such as a Saturday. But do these qualify as earthquake predictions? Not really, since they are just restatements of facts about earthquake activity in California, phrased so that they sound like predictions. They offer no speciﬁc information about year or place of occurrence that would give them real meaning as predictions. So how about this assertion? An earthquake with magnitude of 7.5 or greater will strike Los Angeles, San Francisco, or San Diego sometime between the years of 2010 and 2020.

This statement is more speciﬁc but doesn’t qualify as a legitimate prediction, either, since we just made it up. Even if we believed it (which we do not), you should be wary because we offer no scientiﬁc evidence to support it and give no information about the probability that it will or will not take place. Unfortunately, many such “earthquake predictions” are put forth without supporting evidence by people who are either irresponsible or who simply do not understand probability. And of course, people only remember their predictions if they come true. Predicting Earthquakes Is Difﬁcult How well can scientists predict earthquakes? There have been extraordinarily few successful predictions of the time, location, and size of future earthquakes. In fact, the only truly successful prediction concerning the size, place, and speciﬁc time of a large, damaging earthquake was by Chinese seismologists who anticipated a quake in Haicheng, a city of about 90,000 people in Liaoning Province 500 km east of Beijing. The day before a magnitude 7.3 earthquake occurred at 82

Sidebar 6.1 WHEN WILL THE “BIG ONE” OCCUR IN CALIFORNIA? Nobody knows the day, year, or even the decade when the next earthquake with magnitude of about 8.0 will occur along the San Andreas Fault in California. However, the available scientific evidence indicates that, on the average, such earthquakes strike California about every 50 –150 years. Since almost a century has lapsed since the last great earthquake in California, the San Francisco earthquake of 1906, it is likely that the next “Big One” will occur in our lifetimes. Why do scientists believe that great earthquakes occur in California every 50 –150 years? Prior to the 1906 quake, a great earthquake occurred in 1857 near what is now Los Angeles in southern California. Before that, there are no historical records of earthquakes;

however, near the 1857 epicenter geologists have carefully excavated streams along the fault that were offset by previous large earthquakes (Sieh 1978). By using radioactive dating methods on bits of wood deposited by the streams before and after the offsets, they determined that at least eight large earthquakes occurred, at approximately 1745 a.d., 1470 a.d., 1245 a.d., 1190 a.d., 965 a.d., 860 a.d., 665 a.d., and 545 a.d. Although each individual date had an uncertainty of about 50 years, these data indicate an average interval of 164 years between quakes, with a range from 55 to 275 years. Since these data apply only to southern California, it is plausible that for the entire state the average repeat time is somewhat less (about 50 –150 years).

7:36 p.m. local time on 4 February 1975, because of seismologists’ warnings, city ofﬁcials ordered construction of emergency shelters. On the afternoon before the earthquake they made a public warning and urged residents to stay outdoors, even though it was wintertime, enticing them by showing ﬁlms in the town square. Because of these efforts the city suffered little loss of life. How were Chinese seismologists able to make this prediction? Part of the answer is that China has the most extensive earthquake prediction program anywhere in the world, involving about 10,000 full-time workers and several tens of thousands of part-time volunteers. Policymakers place a heavy emphasis on prediction because China has suffered very severe losses due to the collapse of unreinforced housing in numerous earthquakes; in some sense prediction is the only sensible strategy since it is impractical to replace the entire nation’s housing. Published accounts of the Haicheng prediction (Raleigh and others 1977) demonstrate that it involved several steps that allowed seismologists to deﬁne the time and place where the earthquake would occur. First, at the National Conference of Seismological Work in 1970, seismologists identiﬁed Liaoning Province as a region deserving special attention, and subsequently they set up about twenty new seismic stations and instruments of other kinds. By mid-1974 seismologists had concluded that an earthquake with magnitude of 6 or greater would occur in the province between 1975 and 1977. During the last half of 1974 the anomalous activity gradually intensiﬁed; this included reports of changes in the level and quality of groundwater and even unusual anPREDICTING EARTHQUAKES

83

imal behavior. At a State Seismological Bureau conference in January 1975 seismologists announced that an earthquake of magnitude 5.5 to 6 would occur in the ﬁrst six months of 1975 in the region near Haicheng. On 1 February a small earthquake (M 0.5) occurred for the ﬁrst time near Haicheng itself; then on 3 and 4 February a swarm of larger earthquakes occurred, including eight events with M3. There were also new reports of changes in the water table; artesian ﬂow began abruptly at some sites near the epicenter; and in some cases well water became muddy, while at other sites wells went dry. On the morning of 4 February the Provincial Revolutionary Committee began disaster prevention measures in Haicheng. On the afternoon of 4 February the foreshock activity subsided. This only caused increased concern among the seismologists since their previous experience was “close, successive foreshocks followed by a period of calm, and then the big shock” (Raleigh and others 1977). The scientists believed this period of calm was a ﬁnal precursor. When the earthquake did occur at 7:36 p.m., it destroyed or seriously damaged 90 percent of the structures in Haicheng. Although the Chinese government initially did not release speciﬁc numbers, a 1988 report indicated that the quake caused 1,328 deaths and about 17,000 injuries. Estimates indicate that there would have been 100,000 casualties without the correct prediction (Raleigh and others 1977). The accuracy of the Haicheng prediction and its obvious success in saving lives led seismologists throughout the world to conclude that the Chinese had made signiﬁcant progress on the prediction problem, and many hoped that earthquake prediction would soon be practical throughout the world. In a twist of cruel irony, though, only a year later Chinese scientists failed to predict a magnitude 7.8 earthquake that occurred on 28 July 1976 in the city of Tangshan. This earthquake killed at least 240,000 people, making it the world’s deadliest earthquake in more than three centuries. Tangshan is an industrial city of about one million inhabitants in eastern China, about 150 km from Beijing. When the earthquake occurred at 3:42 a.m. local time, the MMI XI region coincided closely with the city limits of Tangshan; it caused damage to 95 percent of all brick apartment buildings, mostly two to four stories tall, and caused 63 percent to collapse completely (Yong and others 1988). It also ﬂooded coal mines, crippled the railroad system, damaged reservoirs and dams, and collapsed several bridges. In addition, loss of electricity, water, sewage, and telecommunications systems severely hindered rescue efforts as disaster relief units initially experienced considerable difﬁculty reaching Tangshan. 84

T E X A S E A RT H Q UA K E S

Figure 6.1. Magnitude and time of occurrence for foreshocks recorded prior to the Haicheng, China, earthquake of 4 February 1975. (Reprinted from B. Raleigh et al., EOS, Trans. Am. Geophys. Un. 58 [1977]: 236 –272. Copyright © American Geophysical Union.)

The earthquake was not predicted or even expected, as local historical records indicate only one “moderate” earthquake (inferred magnitude 4.75) had struck Tangshan in the preceding six hundred years. In the two years prior to the quake local seismologists had identiﬁed the Tangshan region as a zone of high hazard and were monitoring seismicity, ground deformation, groundwater, gravity, radon, and geomagnetic and geoelectric signals. They had issued crude medium-term forecasts of an earthquake for the region near Tangshan but never speciﬁed the location, time, and size. Prior to the main shock there was no signiﬁcant increase in microtremors, the most important precursor in Haicheng. In Haicheng anomalies had been detected several months in advance and had increased in intensity several days before the earthquake. At Tangshan some signals varied in the day or two prior to the main shock, but there was insufﬁcient time for an evaluation of the situation. The truth is, at present seismologists are not very good at forecasting earthquakes. To seismologists, a successful forecast should include the size and location of a future earthquake, along with a probability that it will occur within some time window. While there has been excellent progress on estimating size and location, the time windows for legitimate earthquake forecasts are usually so large that most people would not call them predictions. Moreover, while the PREDICTING EARTHQUAKES

85

Sidebar 6.2 IS IT TRUE THAT SCIENTISTS REALLY KNOW HOW TO PREDICT EARTHQUAKES, BUT DON’T TELL THE PUBLIC BECAUSE THERE IS SOME KIND OF CONSPIRACY? No. In the past twenty years scientists have spent a lot of time and money trying to learn how to predict earthquakes. Unfortunately, what they found is that predicting earthquakes is one of those problems (like finding a cure for cancer or AIDS) that is much tougher than it

seems. The authors of this book are good friends with many of the scientists who work on the earthquake prediction problem. If the problem had been solved, we would know. Generally, we don’t put much stock in conspiracy theories.

Haicheng prediction is promising, from an American perspective, it is also sobering. It came about in an environment where large numbers of professional seismologists and volunteer workers—far more than anywhere in the United States—were involved in earthquake prediction. It also took place in a society where it is considered good citizenship to heed the advice of experts and the orders of the government. Can you imagine what American citizens would do in a city like Chicago if the local government asked them to sleep outside in February because there might be an earthquake? Finally, if we ever do learn to forecast earthquake occurrence times, we will have to confront some social difﬁculties. Inevitably, if some forecasts succeed, others will be “false alarms,” when an earthquake is forecast but does not occur, and “misses,” when no earthquake is forecast but one does occur. False alarms could cause serious legal and economic problems. Think, for example, what would happen to real estate prices, employment, and tourism in a city like Los Angeles if seismologists predicted that a large earthquake was going to occur there in 2010. Even if the earthquake did occur, the economic losses from depressed real estate values and so forth could well exceed the economic losses attributable to the earthquake itself.1 And if it did not occur, would scientists be held liable for these losses? What Is the Proper Response to an Earthquake Prediction? What should you do if you read that someone has predicted an earthquake? The answer depends on who made the prediction. Many predictions are made by unqualiﬁed individuals and should be ignored. For example, in 1990 a climatologist named Iben Browning announced a 50 percent chance that a big earthquake would occur in the Missouri-Tennessee region on 3 December, at the time when solar and lunar tides were to be especially strong. Browning had no background in seismology; his Ph.D. was in biology from the University of Texas at Austin in 1948.2 He was unwilling to publish an account of the tidal theories that led to his prediction, and he steadfastly refused to discuss the basis of his prediction

86

T E X A S E A RT H Q UA K E S

with legitimate scientists, preferring instead to communicate only with the press. The entire earthquake community repudiated the prediction except for one seismologist, David Stewart, who in the past had lost credibility among seismologists because he publicly endorsed the use of paranormal means for predicting earthquakes. Under these circumstances, how could anyone take Browning’s prediction seriously? Many people did. In some communities schools were closed, and there was a boom in the sale of earthquake insurance. The predicted earthquake never occurred. In contrast, in 1985 seismologists at the U.S. Geological Survey forecast that a magnitude 6 earthquake would occur near Parkﬁeld, California, before 1993. When a magnitude 4.7 earthquake occurred on 20 October 1992, they raised an “A-level alert,” signifying a 37 percent probability that the forecasted earthquake would occur within seventy-two hours. Once again, the earthquake never occurred. However, while many seismologists raised technical questions about the basis of the forecasts, all would agree that the forecasters were responsible, legitimate, professional seismologists and that their forecasts deserved to be taken seriously. It might be difﬁcult for the public to ﬁgure out who is a legitimate professional and who is not. For example, consider the predictions made in Greece using the so-called VAN method, an acronym formed from the ﬁrst letters of the last names of its inventors, three Greek physicists named Varotsos, Alexopoulos, and Nomicos. In the early 1980s the VAN scientists began making continuous measurements of the earth’s natural electric ﬁeld at about ﬁfteen stations located throughout Greece. They claimed to observe “seismoelectric signals” (SES) occurring prior to a number of earthquakes (Varotsos and Alexopoulos 1984a; 1984b), and thus began a regular program of using SES to predict earthquakes in Greece. In their publications they have claimed to be highly successful, even though in some cases when earthquakes did occur, they were much smaller than predicted or situated hundreds of kilometers from the site of the SES precursors. Most legitimate seismologists consider the VAN predictions to be vague, illposed for hypothesis testing, and entirely without scientiﬁc merit. Over the years, as the VAN group persists in claiming success in newspaper articles, published criticisms of the VAN method in scientiﬁc journals have become increasingly strident. For example, the title of a scientiﬁc analysis of the method was

PREDICTING EARTHQUAKES

87

“VAN Method Lacks Validity,” the analysis had section subtitles of “No Physics,” “No Science,” “No Prediction,” “No Success,” and “No Way” (Jackson and Kagan 1998). Such a decidedly nasty tone is almost unheard of in the gentlemanly and ladylike world of published scientiﬁc discourse. So how is the public to know whether the VAN scientists or their critics are right? After reviewing the available literature (Lighthill 1996; Geller 1996),3 the authors of this book conclude that the VAN scientists are either incompetent or charlatans, or both; we ﬁnd no evidence of validity for the VAN method. Yet how could ordinary citizens without special training in seismology know this, considering that the VAN scientists are legitimate physicists who have produced a long list of publications? The Search for Precursors For scientists to predict an impending earthquake successfully, they must identify a precursor, a phenomenon that occurs just prior to the beginning of the earthquake rupture process. Or if some measurement indicates crustal stresses are approaching the breaking strength of rock, scientists could forecast that earthquake probability is especially high, even if they could not predict the occurrence time. What are these precursory phenomena, or what might scientists monitor to assess crustal stress levels? Foreshocks and Gaps

Perhaps the most direct indicator that a fault may rupture is the sudden onset of small earthquakes in a region where there has been little activity, as in Haicheng. Clearly, the small earthquakes themselves occur because stress is causing movement along a fault. Their occurrence could indicate that a previously “locked” portion of the fault is beginning to rupture, or the fault movement associated with them could increase the stresses on a neighboring section of the fault. Along a well-deﬁned, active fault such as the San Andreas in California where historical records or geological formations indicate that large earthquakes once occurred, the absence of earthquakes may well indicate that the fault is locked and stress is building up for a future earthquake. Seismologists who undertake statistical searches for these seismic “gaps” believe they are especially ripe for an earthquake when the activity begins after a long period of quiescence. However, not all seismologists are convinced that seismic quiescence is, as yet, a veriﬁable precursory phenomenon. In spite of an impressive list of publications 88

T E X A S E A RT H Q UA K E S

that support it, an international panel that assembled to evaluate possible precursors voted neither to accept nor reject seismic quiescence as a legitimate earthquake precursor (Wyss 1997). Geodetic Phenomena

Often in the hours or days before a fault ruptures in an earthquake, the buildup of stress will cause the two sides to creep slowly past one another. This can cause almost imperceptible deformation of the crust or tiny changes in elevation, measurable by tiltmeters or by geodetic techniques that precisely measure distances between points near the fault. The stress causes the surface of the ground to deform, just like when you push along the edge of a foam rubber mattress, creating bulges and little valleys in the surface. Groundwater and Hydrological Precursors

As stressed rocks near their breaking point, microscopic cracks form. Indeed, one model of earthquakes is that rupture occurs when these tiny cracks become numerous enough to coalesce, forming a rupture surface. Since many crustal rocks are already porous, the opening of additional cracks may affect the natural ﬂow of groundwater. Thus, before an earthquake, well levels can go up or down if there is enhanced groundwater ﬂow toward or away from the well. The added ﬂow may cause some wells to become muddied or even produce artesian phenomena where the water table rises enough to make water ﬂow out onto the earth’s surface and cause local ﬂooding. Electromagnetic Phenomena, Radon Gas

As stress induces hydrologic changes, these in turn may induce other precursors. For example, just as electric currents ﬂowing in the atmosphere occasionally become evident when a thunderstorm occurs, the earth’s crust also carries electric currents. Groundwater affects these currents signiﬁcantly since water conducts electricity much better than rock does. Therefore, in the hours or days before a major earthquake, changes in the subterranean currents and in the electric potential (voltage) could be measured between points of the earth’s surface in the epicentral area. Because electric currents produce magnetic ﬁelds, the changes in these currents cause changes in local magnetic ﬁelds. Similarly, the opening of cracks allows gases to ﬂow more easily. One such gas is radon, produced continually by the natural decay of radioactive elements that are a constituent in ordinary rocks. Since radon is itself radioactive, it is relPREDICTING EARTHQUAKES

89

Figure 6.2. Distribution of incidents of unusual animal behavior reported prior to earthquakes, sorted according to the distance from the epicenter and the time before the quake. (Reprinted from R. E. Buskirk et al., Rev. Geophys. Space Phys. 19 [1981]: 249. Copyright © American Geophysical Union.)

atively easy to measure with special canisters placed underground. Because radon is not produced by any ordinary biological process, increases in the radon level may indicate that rupture is about to occur. Animal Behavior

Is it true that some animals can sense earthquakes before they occur? This idea is partly true. Fifty years ago most scientists thought this was just a crackpot idea, like ESP or UFOs. However, several things have changed their opinion. First, enough reliable reports of peculiar animal behavior prior to some earthquakes have made it clear that sometimes these reports are true (ﬁgure 6.2). Numerous such reports preceded the Haicheng earthquake, and an international review of the prediction noted that “even the more skeptical Chinese scientists seem convinced that such behavior does indeed occur” (Raleigh and others 1977). Some of the unusual behaviors reported (such as snakes that came to the surface of the ground even though it was winter) are almost certainly related to changes in the water table. Moreover, laboratory investigations have shown that some species of animals 90

T E X A S E A RT H Q UA K E S

are considerably more sensitive than humans to certain stimuli (Buskirk, Frohlich, and Latham 1981). For example, many kinds of ﬁsh have sensory organs on their skin that make them very sensitive to vibrations or water movement. This helps them avoid predators, and it makes it possible for them to move around together in “schools.” Bees and some birds are more than a million times more sensitive than humans to magnetic ﬁelds. Catﬁsh and sharks are at least a million times more sensitive to electric ﬁelds. A million times. Think of it! If you were a million times more sensitive to electromagnetic ﬁelds, you could sense that it was raining outside or know another person had entered the room, all without using your eyes and ears. Thus it is plausible that animals sometimes sense and are disturbed by stressinduced changes in the water table that also affect electromagnetic ﬁelds. Or they may respond to precursory earthquake waves that are imperceptible to humans. We humans generally rely so heavily on our vision that we tend to ignore other stimuli, even when our four other senses are capable of perceiving them. It is unlikely that scientists will ever use animals to predict earthquakes. The precursors animals sense are not observed before all earthquakes. Also, animals, like humans, are notoriously unreliable, as they tend to respond to signals differently at different times. Even if animals do ever help us to discover reliable earthquake precursors, the sensible course would be to build instruments to monitor these precursors. What Precursor Is Best?

We have just described several precursors that may precede earthquakes, and it might seem as if predicting earthquakes is easy. All you have to do is start monitoring microtremors, groundwater, electromagnetic ﬁelds, and so forth. For several reasons, however, it isn’t this simple. First, many of the precursors described above occur only within the epicentral area, even though the earthquake itself may cause severe damage at distances of tens or hundreds of kilometers. The epicentral region may be only a few kilometers in extent. Since groundwater and electromagnetic ﬁeld variations are somewhat quirky, one would need to see signals on several monitors before being convinced that a precursor was occurring. Unless there are special reasons to believe that a speciﬁc, small region is likely to experience a major earthquake, it simply is not feasible to place monitoring devices at, say, 1 kilometer intervals over the entire state of California. While most seismologists would agree that foreshocks or unprecedented PREDICTING EARTHQUAKES

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earthquake swarms are the most convincing precursors, these don’t occur only before large earthquakes. How can you tell whether a small earthquake is a foreshock, or just a rare small earthquake, until a damaging large earthquake does (or does not) occur? Finally, in numerous cases large earthquakes occur with no foreshocks whatsoever. Like microtremors, all candidates for precursors are phenomena that are “normal” in that they often are unrelated to large earthquakes. For example, groundwater variations, electromagnetic ﬁeld changes, and even peculiar animal behavior are affected by rainfall, atmospheric phenomena, and other factors. With our present level of knowledge, scientists generally use them to make predictions only when several precursors occur in the same time or in places like Haicheng where other data lead seismologists to believe large earthquakes could be imminent. The Future of Earthquake Prediction If reliable earthquake predictions are not possible today, will scientists be able to forecast earthquakes accurately in the future? In fact, over the past halfcentury this question has sparked a major controversy among seismologists. Four well-known seismologists published a paper in the journal Science with the title “Earthquakes Cannot Be Predicted” (Geller and others 1997). In a separate, extraordinarily thorough review article Geller (1997) stated that “earthquake prediction research has been conducted for over 100 years with no obvious successes . . . Reliable issuing of alarms of imminent large earthquakes appears to be effectively impossible.” These scientists downplay the signiﬁcance of the Haicheng prediction, implying that the Chinese claims of success might be greatly exaggerated because of the Cultural Revolution at that time and the enormous commitment that the government had made to the earthquake prediction program. On the other hand, equally reputable scientists believe earthquake prediction is achievable, and they are highly critical of the way that governments in the United States and Japan have administered programs that sponsor prediction research. For example, Chris Scholz (1997), a noted seismologist and rock mechanics expert, states quite seriously: Predicting earthquakes is as easy as one-two-three. Step 1: Deploy your precursor detection instruments at the site of the coming earthquake. 92

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Sidebar 6.3 IF SCIENTISTS CAN PREDICT HURRICANES AND VOLCANOES, WHY NOT EARTHQUAKES? The processes that generate hurricanes, volcanoes, and earthquakes are very different. A century ago people could not predict hurricanes. They knew hurricanes occurred along the Gulf Coast, but they could not predict when. Today, with telecommunications and satellite images, we can watch them develop on television and track them. Improved technology has made it possible to understand their formation and follow their progress. Although it may seem that volcanoes erupt suddenly and unexpectedly, in fact the movement of magma toward the surface takes a long time and is accompanied by observable phenomena. Often, this movement causes small earthquakes as the hot magma forces open cracks and breaks rock. Volcanologists can operate networks of seismographs to locate

these small earthquakes. If they increase in number and move toward the surface, it means there will probably be an eruption. So earthquakes help us predict volcanoes, even though we cannot predict earthquakes. With earthquakes, our understanding is like with hurricanes a century ago. We know where big earthquakes are likely to occur, but not when. Possibly a century from now we may have found the technology to watch them develop and predict them. For example, carefully processed satellite images might somehow allow us to monitor stress and strain continually in the earth’s upper layers. We might then predict earthquakes in places where the buildup was accelerating especially quickly. But for now, this is just a dream.

Step 2: Detect and recognize the precursors. Step 3: Get all your colleagues to agree and then publicly predict the earthquake through approved channels. Scholz notes that the U.S. effort to predict earthquakes has been half-hearted and underfunded. He suggests that for a research subject that is not yet well understood, too much attention was focused on one area—Parkﬁeld, California— where no earthquake occurred while signiﬁcant earthquakes were occurring elsewhere in California (Loma Prieta, 18 October 1989, Mw 6.9; Landers, 28 June 1992, Mw 7.3; Northridge, 17 January 1994, Mw 6.7). Similarly, the Japanese program has concentrated on the area surrounding Tokyo and thus missed the 16 January 1995 Kobe earthquake (Mw 6.9). So, whom should we believe? Although earthquake prediction is a tough problem, the authors of this book are more optimistic, tending to agree with Scholz that the appropriate research has not been done, especially considering the enormous societal costs that would be associated with a magnitude 8 earthquake near a city like Los Angeles or Tokyo. In rock mechanics laboratories, scientists have found that surface deformation changes always precede rupture in samples of crustal rocks and suggest that surface deformations of at least several centimeters occur prior to magnitude 7 earthquakes (Spetzler and Mizutani

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1987). It seems distinctly possible that one could monitor such deformations with a combination of modern satellite-geodetic methods and the use of global positioning system (GPS) technology. Indeed, recent technological progress has made it possible to purchase inexpensive GPS equipment to monitor driving distance in your golf game or the location of your sport utility vehicle. So is it unrealistic to think that future progress might allow us to continuously monitor surface deformation over extended areas? We believe this will happen in the twenty-ﬁrst century, and it will become possible to identify at least some areas where earthquake ruptures are imminent. Yet we must acknowledge it is still possible that scientists may never be able to make reliable earthquake predictions. Some processes are naturally unpredictable, even when we understand how they work. For example, we understand how the Texas lottery works; we can even watch television and see the machine pick the numbers. But no one can predict the winning numbers. Even though the physics of bouncing balls is well understood, which ball bounces around and ﬁnally falls depends on too many tiny details that will always be unknown to us. Similarly, it is possible that the triggering process that controls the exact time and place of an earthquake depends on small details of rock properties and fault structure that will always be unknowable. And if the time scale of the triggering-to-rupture processes was often quite short—say, an hour or less—it might not be possible to detect precursory phenomenon. Notes 1. A somewhat analogous situation occurs when hurricanes threaten cities along the Texas Gulf Coast such as Galveston, whose economy depends on tourism. If a hurricane is in the Gulf, authorities make television and radio announcements discouraging tourists from coming to Galveston even though no one knows in advance where the hurricane will make landfall. This is frustrating for Galveston merchants, who will tell you that “we have survived many hurricanes, but we can’t survive if the tourists don’t come.” 2. The title of Iben Browning’s 1948 doctoral dissertation at the University of Texas was “Relation between Ion Action and Osmotic Pressure on a Ciliate Protozoan.” 3. We are aware of only one scientist who is widely respected by U.S. seismologists, Seiya Uyeda, who has publicly supported the use of the VAN method (see Uyeda 1998).

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CHAPTER 7

SHOULD I WORRY ABOUT EARTHQUAKES? Just Deserts or Just Desserts? We are always saddened when people are hurt or property is damaged by a natural disaster. Some disasters are especially poignant because it is clear that much of the suffering they produced could have been avoided. On beaches along the Texas Gulf Coast we see housing developments that are certain to be destroyed by the next serious hurricane. We have seen pictures of beautiful homes in California built on steep slopes that are likely to fail—homes that will succumb to a landslide triggered by heavy rains or by an earthquake. Often the people who live in these homes are unaware of the potential for disaster. For example, one of this book’s authors (Frohlich) once bought a home in Austin along a sleepy little creek, only to discover later that the house had been ﬂooded during the 1981 Memorial Day ﬂood. Perhaps you could say he got just what he deserved, considering that he is a professional earth scientist who should have known better. “I just wasn’t thinking” is all he can say about it now. While we are thinking, should we as Texans make any special preparations for earthquakes? Or is the risk in Texas so low that we can afford to see earthquakes simply as a colorful but unreal hazard, contributing images and names to products such as the video game Quake, Aftershock liqueur, and a recipe for earthquake chocolate cake?

Insurance Does your homeowners insurance policy cover earthquake damage? Almost certainly not. You are not covered unless your policy explicitly speciﬁes that it covers earthquake damage and you have paid a separate premium for this. Homeowners insurance is strictly regulated by Texas state law, and insurers must provide information to the Texas Department of Insurance about earthquake coverage. In 1996 insurance companies only collected $2.8 million in earthquake premiums for the entire state of Texas. Half of this amount was collected by two companies, Aetna (recently sold to Travelers) and Employers Insurance of Wassau. Most of this was sold to commercial businesses, not for homes. Apparently, none of the larger homeowners insurance companies in Texas offers earthquake insurance. If you do decide you want earthquake insurance, you might be out of luck. The authors of this book recently made about forty telephone calls and did not ﬁnd any major company that offers earthquake insurance to Texas homeowners. 95

Sidebar 7.1 EARTHQUAKE CHOCOLATE CAKE 1 3 1⁄ 2 oz. can coconut 1 18 oz. box German chocolate cake mix 1 lb. powdered sugar 1 tsp. vanilla 1 cup chopped nuts 1 stick butter (4 oz.) 1 package cream cheese (8 oz.) Preheat oven to 350 F. Soften margarine and cream cheese. Grease and flour a 9x13-inch

pan. Place coconut and nuts in the bottom of the pan. Mix cake as directed. Pour over the coconut and nuts. Mix butter, powdered sugar, cream cheese, and vanilla. Spoon the mixture over the uncooked cake mix. Bake about 45 minutes until cake tests done. This recipe comes from the Citizen Police Academy Alumni Association of Pearland, Texas. It is an “earthquake” cake because when it cools, it cracks on the top and looks like the earth after a quake.

We did learn that, unlike rates for homeowners or auto insurance, the rates for earthquake insurance are unregulated by Texas state law. This means that if you do obtain insurance from an independent company, the company can charge you whatever it pleases. Does this mean that in Texas, earthquake insurance is just a rip-off or a scam? Not necessarily. However, since the major insurance companies do not offer earthquake insurance to homeowners, I would be suspicious of anyone who approached me offering to sell a policy. If you do want to purchase earthquake insurance, call your insurance agent. He or she probably cannot write you a policy but should be willing to help you ﬁnd an independent company that will. One independent agent we talked to stated that one ought to be able to ﬁnd earthquake insurance for a $100,000 home for $100 a year or less. Other agents we talked to thought it would cost considerably more than that because so few policies are sold. Why don’t more companies offer earthquake insurance to Texas homeowners? Rare but catastrophic occurrences that affect a large geographic area, such as earthquakes or hurricanes, pose a difﬁcult problem for insurance companies. For decades at a time companies may collect premiums for earthquake insurance that far exceed claims. For example, between 1990 and 1996 in Texas, claims paid for earthquake damage amounted to only about $275,000, or 2 percent of premiums collected. Market forces thus drive down premiums; or if premiums stay high the public suspects some kind of rip-off. However, when a truly serious earthquake does occur, claims may far exceed the resources of even the largest companies. Thus insurers cannot win, no matter what happens. For these reasons, federal or state governments sometimes form a “catastrophe pool” to provide insurance for catastrophes such as hurricanes, ﬂoods, or earthquakes. This protects homeowners and makes it feasible for mortgage lend-

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Figure 7.1. The Jim Beam brewing company markets Aftershock, an ultrasweet, cinnamon-flavored liqueur. The advertising notes that large sugar crystals that precipitate in the bottle’s bottom are like “geological formations.” Some bottles are marketed with special shot glasses embossed with an “Aftershock Richter Scale.” Photo by Cliff Frohlich. Used with permission.

ers to ﬁnance homes even in catastrophe-prone areas. There is no catastrophe pool for earthquakes in Texas. Do Texas residents need earthquake insurance? For most Texans, the answer is “No.” Most of Texas has experienced no seriously damaging earthquakes within the past 150 years. As described in chapter 2, most of the rare earthquakes

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Figure 7.2

that did cause damage simply broke a few pieces of china. In many areas the chances are slim to none that a damaging earthquake will occur in the next 150 years. Although El Paso, much of far West Texas, and most of the Panhandle have experienced earthquake-induced shaking of MMI V or greater, the risk is still miniscule in comparison to cities like Los Angeles, San Francisco, Seattle, and Quebec. Thus we do not recommend that you buy earthquake insurance for your home in Texas unless you are a worrier and insurance makes you comfortable. If you are the kind of person who worries about uninsured risk to your home, termites are a far more serious problem in Texas than earthquakes. An expert on urban entomology at Texas A&M University told us that in many parts of Texas 40 percent of all homes have termites and 90 percent of homes do that are older than forty years. Homeowners insurance seldom covers termite damage. Home and Ofﬁce If you are building a home or making substantial improvements on your home or ofﬁce, what should you do to make sure occupants are safe if an earthquake occurs? As stated above, you should be aware that hurricanes, ﬂoods, and tornadoes are all much more serious threats than earthquakes in Texas. And while

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Figure 7.3.

most urban areas of Texas have many regulations concerning housing construction, none of these speciﬁcally targets earthquake problems. However, if you are the kind of person who worries anyhow, or if you are moving to an earthquake-prone state and just want information, we recommend the book Peace of Mind in Earthquake Country (Yanev 1991). Although the book is written for people living in the western United States, it thoroughly discusses earthquake-resistant construction methods and points out what types of construction are particularly dangerous and what types generally safe. As a general rule, keep in mind that most deaths in earthquakes occur when heavy objects fall on people, such as chimneys, unreinforced walls, pieces of concrete, or even bookcases. So the preventive strategy is to reinforce structures when they are built and not have bedrooms next to chimneys and such. For preventing property damage, the general approach is to securely connect the various pieces of a structure so that they do not fall apart or come off the foundation during an earthquake. For older homes, this may involve strengthening walls with plywood and using steel straps to connect parts of the structure. Heavy and possibly unstable furniture such as bookcases should be ﬁrmly attached to the walls.

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You may wonder why the government does not pass laws to make people build all buildings so strong that earthquakes do not damage them. While many areas of the United States have such laws, Texas does not. Even in California the building codes do not require structures to withstand really large, nearby earthquakes. It would be very expensive to make all buildings strong enough to survive all earthquakes; to do this would mean that building or renting houses would cost signiﬁcantly more than it does now. People and the lawmakers they elect have to decide how to balance safety and cost. Just how safe is safe enough? How costly is too costly? This is actually a familiar problem that society faces— in auto and airline safety, for example, as well as protection from earthquake damage. Government does assess relative earthquake hazard in different parts of the United States and presents this information in maps (ﬁgure 2.10).1 You should remember that these maps are not perfect. The scientists who make them rely heavily on information about historically recorded earthquakes. Since the repeat times for some kinds of earthquakes might be one thousand years or more, it is always possible that an earthquake can occur that is unlike any in the historical record. For example, would we have any idea that a magnitude 8 earthquake was possible in the Missouri-Tennessee-Kentucky area if we didn’t know about the 1811–1812 New Madrid quakes? These events, possibly the largest earthquakes ever to occur in the continental United States, occurred along a buried fault. A thick layer of sediments deposited by the Mississippi River obscures this fault so that it is virtually invisible at the surface. Similarly, many faults are buried in Texas, especially beneath the thick sediments along the Gulf Coast, although it is unlikely that large earthquakes will occur there. If you look at fault maps you will ﬁnd that most mapped faults are in areas where bedrock comes to the surface and where it is thus easy to ﬁnd faults. There are probably as many faults in heavily sedimented areas, but they just are not on the maps.

The Long and the Short of It Should you worry about earthquakes? In this book, written for Texans about earthquakes, this is the shortest chapter. That should tell you something. This chapter would have been much longer if the book were written for citizens of California, Washington, Utah, Missouri, or about twenty-ﬁve other states where

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Sidebar 7.2 SHOULD WE WORRY ABOUT TSUNAMIS ALONG THE TEXAS COAST? A tsunami, popularly called a tidal wave, occurs when a large volume of seawater is suddenly displaced upward or downward, causing an ocean wave that can travel many thousands of miles. The usual causes of tsunamis are large undersea earthquakes that displace the ocean floor, or huge coastal landslides that displace water when above-water material slides into the ocean. When the tsunami wave arrives at a coastline it breaks and runs up onto the beach like any other wave. However, it can cause damage and loss of life because it may be a lot bigger than ordinary waves. It is unfortunate that tsunamis are called tidal waves, since their origin has nothing to do with true ocean tides. There have been no large tsunamis along the Gulf Coast in historical times. This is because no really large undersea earthquakes have occurred in the Gulf of Mexico. It also does not have any coastal boundaries that produce large landslides. The only tsunamis reported in Texas were observed in Galveston in 1918 and 1922; both were quite small—the largest wave heights were only 60 cm (Parker 1922; Lander and Lockridge 1989). They were attributed to earthquakes that occurred in Puerto Rico; however, this is disputable because the accused earthquakes were both relatively small and didn’t cause tsunamis elsewhere. Geologists have found possible evidence of

one Gulf tsunami that occurred 65 million years ago, when an asteroid 10 km in diameter struck the earth near Mexico’s Yucatan Peninsula. This must have been more devastating than the largest earthquakes, as it produced so much dust that it probably temporarily changed the earth’s climate and possibly caused the extinction of the dinosaurs. It also may have produced a truly enormous tsunami, as some geologists believe they have found evidence of its effects hundreds of kilometers from the Gulf Coast. Two fairly recent movies, Deep Impact and Armageddon, have explored what would happen if an event like this were to occur today. Finally, several natural phenomena other than tsunamis can produce large waves or unusually high sea levels. In Texas the high winds and low barometric pressures associated with hurricanes can cause sea level to rise as much as ten feet and swamp coastal cities. This is known as a storm surge; these, too, are sometimes incorrectly called tidal waves, possibly because the water rises relatively slowly, like the tide, and because they can be most serious if they occur near the time of high tides. The 1900 Galveston hurricane that killed 6,000 people was accompanied by a particularly horrible and famous example of a storm surge.

the earthquake hazard is much greater than in Texas. The truth is, most Texans do not need to worry much about earthquakes. On the other hand, most Texans probably do not worry about earthquakes as much as they should. As described in chapter 2, two areas of Texas—West Texas and the Panhandle— do regularly have moderate-sized earthquakes and have the potential for larger events. In these areas, a thinking citizen would probably avoid living in an adobe structure or one made of unreinforced concrete. Throughout Texas people involved in designing large critical structures such as multistory buildings and highway interchanges should consider how earthquakes, even fairly distant ones, might affect these structures.

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Figure 7.4. The Earthquake is the largest and sweetest sundae sold at Swensen’s ice cream parlors. Photo by Tom Frohlich. Used with permission.

Now, about those sleepy little creeks, telltale hurricanes, and pesky tornadoes . . . Note 1. Various such maps are available online at http://geohazards.cr.usgs.gov/eq/ or obtainable by writing the USGS Information Services at Box 25286, Denver CO 80225.

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CHAPTER 8

WHO ARE SEISMOLOGISTS AND WHAT DO THEY REALLY DO? What Is Their Work? About ten years ago the Department of Geosciences at a well-respected university in Houston wished to hire a new faculty member, and so the department placed an advertisement in EOS, a newspaper sent to all members of the American Geophysical Union, a professional organization for earth scientists. The ad solicited applications from individuals “from any subﬁeld of seismology, including . . .” and listed a half-dozen specializations, such as “imaging reservoirs,” “processing of multifold seismic data,” “seismic interpretation,” and “controlled source seismology.” The remarkable thing about this was that the listed subﬁelds did not include earthquake seismology or any subﬁeld of earthquake seismology. What this advertisement illustrates is that in many parts of the world “seismology” doesn’t mean “earthquake seismology”—it means “oil company seismology.” In places like Houston, where earthquakes pose little or no hazard and oil plays a key role in the economy, a seismologist is someone who works alongside geologists and analyzes signals from man-made explosions. When these “controlled source” explosions are set off in regions where there may be oil or gas, it is possible to produce tomographic images of the subsurface geology and identify promising areas for drilling. In Texas, if you are talking about people who study earthquakes, you need to call them “earthquake seismologists,” not just “seismologists.” So if not all seismologists study earthquakes, what do earthquake seismologists study? This sounds like one of those joke questions like “Who is buried in Grant’s tomb?” or “In what year was the War of 1812?” However, as we shall see below, it is actually a good question. Earthquake seismologists really investigate ﬁve different topics: 1. Earth structure: earthquake waves echo off of, or are mufﬂed by, structures within the earth’s crust, mantle, or core; earthquake seismologists learn about the structure by studying the waves. Oil company seismologists use the same methods—but apply them to seismic waves generated by manmade explosions—-to learn about potential oil-bearing structures near the earth’s surface. 2. Tectonics: earthquakes represent motions along faults in the crust and upper mantle and thus reveal information about ongoing geological processes. This information is of interest to geologists.

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3. Discrimination of earthquakes and nuclear explosions: earthquakes and nuclear explosions produce seismic waves that seismographs can measure at great distances; analysis of these waves is usually the most reliable way to detect nuclear explosions. This is politically important, as seismology provides the best means now available to monitor the compliance of all nations with treaties that ban nuclear testing, such as the recently proposed Comprehensive Test Ban Treaty. 4. Earthquake source process: mechanically, what happens at the focus of an earthquake? 5. Seismic risk: in many geographic areas earthquakes represent a real danger to property and human life; seismologists attempt to forecast the location, size, and (maybe someday) the time of damaging earthquakes and evaluate what kind of shaking to expect at critical sites when they occur. Of these topics, only the last two actually concern earthquakes—the rest just use earthquakes as a tool to study something else. Many people are surprised to learn that learning about earthquakes is not really the goal of most seismology research. In lectures to graduate students the authors have occasionally stated that “80 percent of all earthquake research isn’t about earthquakes.” This is arguable, but there is some truth in it. So what do earthquake seismologists really do? Back when we were in school we were frustrated because we liked science, but we couldn’t ﬁnd out what scientists actually did on an average day. After all, it looked cool to walk around in white lab coats with test tubes full of funny-colored liquids that exploded. But what was it like being a scientist, really? One thing nearly all scientists do nearly every day is write. As we were ﬁnishing our education this came as a big surprise to us, particularly since most of our training focused on math and science, not writing. Yet as professional seismologists, we spend perhaps half our time preparing research proposals, articles for scientiﬁc journals, or memos and letters. The work is not all writing, of course. On most days we spend a couple of hours in front of a screen coding and running computer programs in languages like Fortran, C , or Matlab. And most of us spend a lot of time talking or listening— especially since many seismologists are university teachers. Communication is important because the research projects we work on commonly involve several people, and we need interaction to make the projects go forward.

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What Does a Seismologist Do in Texas? Nearly every time we are at a social gathering, someone asks us, “What does an earthquake seismologist do in Texas? Why aren’t you in California?” Clearly, people suspect that we just sit around and every two years or so answer questions for local television stations after a newsworthy quake happens. Sadly, this is untrue; we actually have to work, keeping busy at all times doing research. Universities that aspire to have a national or international reputation employ scientists who have truly global research interests. Thus the research of most Texas earthquake seismologists concerns earthquakes in other places, such as Alaska or New Zealand. As explained above, because seismological methods for investigating earth structure are useful for ﬁnding oil-bearing strata, in earth science departments you often ﬁnd earthquake seismologists where you ﬁnd oilﬁnding seismologists; sometimes they are the same people. In January 2002 the Seismological Society of America website listed 53 members in Texas. Of these, colleges and universities employed 13 as teachers and researchers, 14 were students, and most of the rest worked for oil companies or for geophysical companies that provide services for oil companies. Altogether, about 2,000 people belong to the Seismological Society of America, and roughly one-third of them reside outside the United States. Among the U.S. states, California has the most members, with 567, Colorado has 71 members, and Texas, with 53 members, ranks third. Three other states, Massachusetts, New York, and Washington, have more than 40 members each. While few Texas seismologists focus their research on Texas, several important scientiﬁc questions about Texas earthquakes are waiting to be answered. As explained in chapter 2, the most useful knowledge for assessing earthquake hazard is reliable information about the locations and size of past earthquakes. It is likely that earthquakes have occurred in historical times in parts of Texas that we do not know about, and so they are not listed in chapter 9. It is possible that readers of this book might help us answer some of these questions.1 For example, did earthquakes occur in the Texas Panhandle before 1917? This was the year of the earliest conﬁrmed Panhandle quake that we know of and also approximately when oil and gas were discovered in the Panhandle. This question is important because the Panhandle has had some of the bigger Texas earthquakes, with magnitudes above 5.0, and nearly all the larger ones have occurred near oil or gas ﬁelds. If large earthquakes occurred in the Panhandle before pe-

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Figure 8.1

troleum production began, it would indicate that most Panhandle earthquakes have a natural origin and suggest that even larger earthquakes could occur there. On the other hand, if the Panhandle earthquakes are induced by petroleum production, this implies that earthquakes with magnitudes of 6 or greater are unlikely to occur. Possibly readers of this book may know of diaries or other contemporary accounts that describe earthquakes that occurred before 1917. Alternatively, diaries or journals might minutely describe many kinds of natural phenomena but never mention earthquakes, probably indicating that none occurred. Another important question concerns earthquakes that might have occurred in West Texas, especially near El Paso. El Paso now has a metropolitan population of almost 700,000; it has experienced numerous local earthquakes since 1889, but all had small magnitudes—less than 5.0. Is it possible that much larger earthquakes could occur here? El Paso itself was not settled before 1827, but a Franciscan mission stood south of the river in Juarez as early as 1659. A study of records from this mission, early settlers, or other sources might tell us about severe earthquakes that El Paso experienced between 1659 and 1889. Finally, how strong were intensities in Texas from the 1811–1812 New Madrid earthquake discussed in chapters 2 and 3? Unfortunately, no known felt re106

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Sidebar 8.1 HOW TO FIND INFORMATION ABOUT TEXAS EARTHQUAKES THAT HAPPENED A LONG TIME AGO—LIKE ONE HUNDRED YEARS AGO If we know the date of an earthquake, we go to the library and look for contemporary newspaper stories about it. Sometimes police reports, logs from weather observers, and even scientific journal articles describe it. However, we suspect that Texas earthquakes have occurred that we don’t know about. Since we cannot read every Texas newspaper ever published we won’t find them. Please contact us by mail or email if you know of other Texas earthquakes missed in chapter 9 of this book or if you have important information about any of the earthquakes listed there.2

The 1902 earthquake in Creedmoor, Texas, (near Austin) was “discovered” in this way. A colleague of ours, Wayne Pennington, was giving a popular talk on Texas earthquakes in Austin and stated that no local earthquakes had ever been felt by Austin residents. This provoked Patrick Cassidy, a high school student and history buff in the audience, to tell Pennington about a 1902 newspaper article concerning the Creedmoor quake. Somehow this quake had never before made it into any of the standard seismological lists.

ports from Texas exist for the 1811–1812 quakes, as the intensity summaries for all areas west of the Mississippi River are only estimates (ﬁgure 1.3). Most seismologists would agree that the greatest earthquake hazard in the Dallas–Fort Worth area is from an occurrence of very large earthquakes in the New Madrid zone. But exactly how severe was the shaking in northeast Texas in 1811–1812? Other historical earthquakes in northeast Texas have been small, and consequently little or no effort has been made to build bridges, highway interchanges, hospitals, or other essential structures to withstand earthquakes. Since doing so could be very expensive, we need to learn as much as possible about what actually transpired in 1811–1812. Although no permanent English-speaking settlements existed in Texas in 1811–1812, there may be journals, diaries, reports, etc., from this period and earlier that have not been thoroughly examined. How Does One Become a Seismologist? Most seismologists we know did not start out planning to be seismologists—it just kind of happened by accident. Wouldn’t it seem strange if you asked an eight-year-old boy what he wanted to be when he grew up, and he replied that he wanted to study earthquakes? That kid needs help. One of us (Frohlich) became a scientist because of the Russians. Everyone else in his family was, or wanted to be, a writer, a teacher, an editor, or a librarian. He was a ﬁfth-grader in 1957 in South Dakota when the Russians sent up the very ﬁrst man-made satellite, called Sputnik. Soon after that they sent up a satellite with a monkey in it. If you thought this had no effect on ﬁfth-graders in places like South Dakota, you would be wrong. When Sputnik went up, America went bananas. Why, if those Russians can put a monkey in orbit, they could WHO ARE SEISMOLOGISTS AND WHAT DO THEY REALLY DO?

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just as well put up a man who methodically heaved bombs over the side of the satellite as it ﬂew over Kansas. Obviously the Russian satellites worked better because their schoolchildren studied math and science. Meanwhile, American children shot pool, practiced the twist, dreamed about horsing around at high speed in the back of fast cars, and listened to intellectual stuff like “Purple People Eater” on the radio. And so it came to pass that the Word came down to kids like the author, who had only just begun to shoot pool, that: 1. if you can hack it in the world of math and science, there will be a Very Good Job for you when you ﬁnally get out of school; and 2. not only would this math and science job be good for you, it would be Good for America. So what did our author do? Showing no imagination whatsoever, he decided to study physics, at least until he washed out. Amazingly, he didn’t wash out but did encounter a few twists and turns in the path along the way. As a graduate student he discovered that many physicists were having trouble ﬁnding jobs. Market forces were at work; after Sputnik, too many kids had chosen a career in physics. But market forces work both ways. About this time an oil crisis hit, and the theory of plate tectonics was just becoming accepted; oil companies and universities needed earth scientists. One day, a university technician who was preparing seismographs for a three-month ﬁeld program in New Zealand showed the author a seismograph. Because of our author’s experience in physics labs it seemed elegant and simple to him—just a coil, a magnet, and an ampliﬁer (see ﬁgure 1.7). Two weeks later the leader of the New Zealand program asked him if he wanted to participate in the experiment. He would have to service and deploy the seismographs, and when they did not work he would have to ﬁx them with basic tools, like a voltmeter and a Swiss Army knife. And so our author went to New Zealand knowing nothing about earthquake seismology yet employed as a seismologist. He has been employed as a seismologist ever since. If you have ever thought you might like to be a seismologist, two features of this story are instructive. First, note that the author had a strong background in math and physics before becoming a seismologist. Most seismologists have a Ph.D. in geology or geophysics; this requires several years of school after graduating from college. As undergraduates, both the authors of this book majored in physics and took a lot of math courses. If you are in high school and think seis108

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mology might be a promising career for you, you should be someone who likes math and science and who ﬁnds it easy to learn these subjects. Second, market forces are an extremely important factor inﬂuencing career choice. As described above, the author left physics because jobs were scarce and chose seismology because work in that ﬁeld was available and because his physics background made him eligible for an entry-level job. Now, thirty years later, jobs in earthquake seismology are scarce. So now you probably should not begin a career in earthquake seismology unless you are really, really sure that this is what you want to do. The other author of this book (Davis) was trained as a seismologist but found it difﬁcult of ﬁnd work in the same city as his wife, a mathematician. He now operates his own business designing web pages, a job that did not even exist when he began his training in math and science. Who Are Seismologists, Anyhow? Who is the greatest seismologist of all time, that is, since about 1890 when John Milne invented the modern seismograph? People often disagree about the answers to this kind of question; however, most seismologists would probably pick Beno Gutenberg as the greatest. Gutenberg was a colleague of Charles Richter (of the Richter magnitude scale) and a professor at the California Institute of Technology from 1931 to 1960. The papers and books Gutenberg wrote about his earthquake observations provided the background for much of modern seismology. Most Americans who are not scientists would probably pick Charles Richter as the most famous seismologist. While Gutenberg and Richter did much of their work together, though, on almost all this work Richter was the second author. One of the few papers Richter wrote alone was the 1935 paper in which he proposed his magnitude scale. Although his scale is a useful tool for classifying the size of earthquakes, that paper did not represent a major achievement in seismology. Our own favorite candidate for greatest seismologist is a Japanese man named Kiyoo Wadati, who lived from 1903 to 1995. Between 1927 and 1936 Wadati published a series of extraordinarily important scientiﬁc papers. These papers: 1. provided the ﬁrst believable proof of the existence of “deep earthquakes”— quakes occurring at depths of 70 to 650 km beneath the earth’s surface; 2. provided a model of the earth’s velocity structure that was as good as similar models proposed by Gutenberg and others; and WHO ARE SEISMOLOGISTS AND WHAT DO THEY REALLY DO?

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Figure 8.2

3. described the geometry, geological character, and possible cause of deep earthquake zones—thirty years before other scientists published similar descriptions. Strangely, even though Wadati published his papers in English they are often ignored, possibly because his country, Japan, lost World War II and because during the next two decades Japanese scientists were less involved than American or European scientists in the research that led to the acceptance of plate tectonics. Because earthquake seismology is a relatively young science— only about a century old—many of the ﬁnest seismologists of all time are still alive. However, because we don’t want to hurt anybody’s feelings, we will refrain from trying to choose the greatest living seismologist. Have there ever been any famous women seismologists? Actually, female seismologists were quite rare until about thirty years ago. However, it was a woman, Inge Lehmann, who discovered in 1936 that the earth’s liquid core had a solid, inner core at its center. Inge Lehman was a most remarkable woman. She was born in Denmark in 1888 and educated in a school run by the aunt of physicist Niels Bohr. In this school, as she said, “no difference between the intellect of boys and girls was recognized, a fact that brought some disappointments later 110

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in life when I had to realize that this was not the general attitude.” It was not easy for a woman to carry on a scientiﬁc career in the ﬁrst half of the twentieth century. Lehman said, “You should know how many incompetent men I had to compete with—in vain.” In spite of these difﬁculties she was feisty enough to succeed as a seismologist. Her discovery of the inner core is one of major seismological accomplishments of the twentieth century. And she managed to outlive almost everybody who ever failed to respect her abilities; she died in 1993 at the age of 104. Nowadays, female seismologists are quite common. For example, in California, Barbara Romanowicz directs the University of California at Berkeley Seismological Laboratory, one of the world’s oldest and most revered seismology research laboratories. In Texas, Diane Doser is a professor at the University of Texas at El Paso; as part of her work she operates several seismograph stations in West Texas. Both of these women are excellent scientists who are respected internationally for their earthquake research. Notes 1. To address these questions, Perez (2001) made a preliminary search of historical Panhandle newspapers archived at the Texas State Historical Association in Austin. However, she was unable to ﬁnish searching the material, and she found that many early newspapers were not in the archives. Thus there are still opportunities for amateur historians/seismologists to uncover useful information. 2. The mailing address is: Cliff Frohlich, Jackson School of Geosciences, University of Texas, Austin TX 78713. The email address is: [email protected].

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CHAPTER 9

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS The objective of this chapter is to summarize available knowledge about all historical earthquakes felt by Texas residents. Most of the events here are actual earthquakes that occurred within Texas borders. A few are earthquakes with epicenters outside of Texas, and still others are events reported by the media as earthquakes that in all likelihood were something else, such as sonic booms or thunderstorms. We do not include events such as the 1947 ammonium nitrate explosion in Texas City or the 1992 natural gas explosion in Brenham, which were recorded by seismographs but that to our knowledge were not mistakenly identiﬁed as earthquakes by media sources. For each compendium entry we provide full reference information so that interested readers can ﬁnd original source information. For felt report information, the best data and the most colorful stories often come from newspaper articles; thus following many entries we include a summary of the papers, dates, and article headlines that report about the earthquake. For epicenter information, different agencies or investigators often report different locations for the same earthquake. To avoid confusion we here present only one location for each event and refer to sources that give other locations. In contrast, for earthquake magnitudes we generally present the magnitudes reported by various agencies. This is because estimates of earthquake magnitude are highly uncertain, especially for historical events. Even for recent earthquakes magnitudes can vary widely depending on the magnitude scale used (table 9.1). When several magnitudes are available the ﬁrst one presented is the one we believe is most reasonable. To specify the times that earthquakes occur we use Coordinated Universal Time (UTC).1 This is six hours later than Central Standard Time and ﬁve hours later than Central Daylight Time. If you read that an earthquake occurs at 15:00 UTC, for Texans this is 11 a.m. local standard time and noon local daylight time. UTC is the common choice of seismologists, astronomers, airline pilots, and military personnel to specify time when there is a need to be precise about events like earthquake waves that commonly travel across more than one time zone. New Madrid Region—1811 and 1812 The region that is now Texas was only sparsely settled in the early 1800s, and we know of no reliable accounts of earthquake activity before 1847. The ﬁrst documented earthquakes that may have been felt in Texas were the great New Madrid, Missouri, earthquakes during the winter of 1811–1812. Although the earthquakes were felt strongly in Louisiana (Davenport 1812; Peterson 1933; 112

Table 9.1 / EXPLANATION OF ABBREVIATIONS FOR DIFFERENT MAGNITUDE SCALES mb

Magnitude based on amplitude of short-period body waves

mb0.4 Hz

Magnitude based on ampiltude of 0.4Hz body waves

mbLg

Magnitude based on amplitude of Lg phase on short-period seismograms

Mc

Magnitude based on the length of the coda (i.e., the duration of the signal on a short-period seismogram)

Mcorr

“Corrected” magnitude—a magnitude adjusted after a special study

mDUR

Magnitude based on the duration of the signal on a short-period seismogram

mf

Magnitude based on the area (in km2) over which earthquake was felt

mIV

Magnitude based on the area (in km2) of the region where MMI was IV or greater

mN

Magnitude based on the area (in km2) of MMI isoseismals

ML

“Local” magnitude— determined using methods applicable only to a particular seismic station

MS

Magnitude inferred from the amplitude of 20-second surface waves

Mw

Magnitude inferred from scalar seismic moment

NEW MADRID REGION — 1811 AND 1812 Origin times:

Locations:

Felt areas (all): Magnitudes:

(a) 08:15 UTC (16 December 1811) (b) 15:00 UTC (23 January 1812) (c) 09:45 UTC (7 February 1812) (a) 36.0 N 90.0 W (b) 36.3 N 89.6 W (c) 36.5 N 89.6 W 5,000,000km2 (a) Mw 8.1 (b) Mw 7.8 (c) Mw 8.0

Nuttli (1982)

Nuttli (1982) Johnston and Schweig (1996)

Nuttli 1973; Coffman, von Hake, and Stover 1982), no intensity data are available from Texas or most areas west of the epicentral region. Nevertheless, if the felt areas were roughly symmetrical about the epicenter, intensities in northeast Texas could have reached MMI VII. It is popularly believed that the New Madrid earthquakes formed Caddo Lake in northeastern Texas and northwestern Louisiana. According to Caddo Indian legend, the lake was formed by an earthquake caused when a Caddo chief failed to obey the Great Spirit (Shreveport Times 13 March 1955; McClung 1974). One published report (Burr 1943) cites the existence of Indian utensils, arrowheads, A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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Figure 9.1. Estimated felt area map for the New Madrid, Missouri, earthquake of 16 December 1811. There were no felt reports in Texas due to the low population density in 1811. Isoseismal lines shown were inferred by Carlson (1984) from a summary of felt reports from east of the Mississippi River as reported by Nuttli (1973). Some authors have ascribed the formation of Caddo Lake in northeast Texas to the 1811–1812 New Madrid earthquakes. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate present-day county boundaries.

and pottery beneath the lake as evidence of a sudden inundation such as might occur if the lake formed or was deepened by an earthquake. However, Caddo Lake apparently existed as a large swampy area long before 1811 and was caused by a giant logjam known as the Great Raft that was noted as early as 1722 (Carruth 1970). Because the lake level has changed several times in the past one hundred years (Shreveport Times 7 March 1953; see also McClung 1974), the presence of Indian artifacts beneath the lake is not particularly surprising, and it is not clear whether the artifacts suggest the destruction of a village or were merely items left behind by the Caddo Indians. Thus the available information neither 114

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SEGUIN — 14 FEBRUARY 1847 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

02:00 UTC (approx.) 29.6 N 98.0 W V 1,200km2 mN 3.6

Davis and others (1989) Davis and others (1989) (This study) ”

proves nor disproves that earthquakes are responsible for the deepening of Caddo Lake. Other sources that mention the 1811–1812 New Madrid earthquakes include Fuller (1912), Marvin (1896), McKeown (1982), and Nuttli (1982). Later, smaller earthquakes from the New Madrid region were felt at large distances to the southwest. The 31 October 1895 earthquake with a magnitude mN of 6.2 was felt in New Mexico, and an earthquake on 1 October 1971 with mbLg of 4.1 was felt with intensity I–III in Nacogdoches, Texas (Nuttli 1979). A New Madrid shock on 17 September 1938 with mN of 4.2 was felt nearly as far west as Texas (Walter 1939; Neumann 1940b). Headline

Atlantic Monthly, “Earthquakes of the Western United States,” November 1869

Seguin—14 February 1847 The ﬁrst known Texas earthquake, unlisted in earthquake catalogs until recently, was felt in Seguin and New Braunfels, where it cracked timber and frightened residents. According to the Houston Democratic Telegraph and Texas Register of 1 March 1847: A severe shock of an earthquake was felt at Seguin and New Braunfels, on the evening of the 13th February, about 8 o’clock [02:00 UTC on 14 February]. The shock lasted nearly a minute, and the houses were rocked so as to cause the timber to crack, and for a few moments the inhabitants were fearful that the roofs would fall in. Just before the shock was felt, a heavy rumbling sound was heard, coming from the Southwest. This, we believe, is the ﬁrst shock of an earthquake that has been noticed in that section for many years.

“Several long minutes trembling of the ground” also were felt by Charles Pressler, a surveyor, on his way from Austin to Rio Blanco around 8 o’clock that night. He had left Austin on 10 February, although his exact location at the time of the shock is unclear. Pressler (1847) also noted “the Austin paper wrote that Seguin . . . felt it quite a bit.” Headline

Houston Democratic Telegraph and Texas Register, 1 March 1847: “Earthquake”

Austin—1850s (Probable spurious earthquake report) Two editions of the Austin Daily Tribune in 1902 report an earthquake in Austin during the 1850s. The ﬁrst story noted: A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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MANOR — 1 MAY 1873 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

04:30 UTC 30.25 N 97.6 W III–IV local mN 3.1; 3.6

Docekal (1970) Docekal (1970) Davis and others (1989); Nuttli (1979)

An old citizen who resided in Austin sixty years, was among a little knot of citizens gathere [sic] on a corner one day last week . . . “In the ﬁfties,” he said, “an earthquake was felt in Austin. It was a shaker and there is no doubt about that . . . If the buildings of the present time had been built then there is no doubt in my mind but that the earthquake would have tumbled some of them over. “Queer weather prevailed during the shaker’s visit. There was no noise, but just a shaking. The Colorado River reversed itself and moved upstream and hundreds of ﬁsh were killed, ﬂoating to the surface. Everybody in Austin was terriﬁed.”

The second article was similar, although surprisingly enough it contradicted the ﬁrst article by stating that the weather was normal and that the earthquake was accompanied by a deep rumbling: About the year 1852 along in the fall Captain W. M. Wilson, an old citizen of Austin, was building a ferry boat at Old Stone’s ferry, not very far below East Avenue. Suddenly he and his workmen were startled by a deep rumbling, and accompanying it was a violent tremor of the earth. The water in the Colorado River suddenly began to move upstream . . . After the river had resumed its natural course many dead ﬁsh ﬂoated to the surface . . . There was nothing unusual in the weather.

A search of local newspapers from the 1850s turned up no original reference to the earthquake (Davis, Pennington, and Carlson 1989). It is possible the story is either ﬁctitious or greatly exaggerated. Headlines

Austin American Statesman, 1 September 1978: “Early Quakes Jolted Austin” Austin Daily Tribune, 18 May 1902: “Austin Has Felt Earthquakes” Austin Daily Tribune, 10 October 1902: “Seismic Disturbance”

Manor—1 May 1873 The New York Times of 12 May 1873 mentioned an earthquake near Manor, Texas. The article reads, in its entirety: Three shocks of earthquake were felt at Manor, Texas about 10 o’clock on the evening of April 30. Houses trembled, doors and windows rattled, and several persons, who were asleep, were awakened.

The newspaper does not mention how it obtained this information. This article, although never directly cited, seems to be the main source of information pub116

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FORT GIBSON, OKLAHOMA — 22 OCTOBER 1882 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

22:15 UTC 35.9 N 95.1 W VIII (in Oklahoma) 740,000km2 mN 5.6; 5.5

Davis and others (1989) Davis and others (1989) (This study) Davis and others (1989); Nuttli (1979)

lished elsewhere about this earthquake. A contemporary earthquake list (Rockwood 1873) includes a brief mention of the Manor event and credits two men from the New York Times for their assistance in compiling the list. Later references to this earthquake (for example, Docekal 1970) list Rockwood as their only source. Davis, Pennington, and Carlson (1989) reported that they searched the Austin Statesman, the Austin Daily Texan, and the Galveston Daily News and found no mention of an earthquake or any unusual disturbance in Manor on 30 April. However, according to the Austin Daily State Gazette of 3 May 1873, the shocks were not felt in Austin: An earthquake is reported in the vicinity of Manor by telegram to the Houston Telegraph . . . It must have been a very slight one not to have been observed in Austin, only twelve miles distant.

Other sources that mention the 1873 Manor earthquake include Comanche Peak Steam Electric System (1977), Reagor, Stover, and Algermissen (1982), and Varma (1975). Fort Gibson, Oklahoma—22 October 1882 This earthquake, felt in northeastern Texas, Oklahoma, Arkansas, Kansas, and Missouri, is one of the largest known earthquakes felt in the eastern half of Texas. Although several felt reports exist from locations experiencing high intensities, there is no agreement as to the location of the epicenter. The ﬁrst assigned location (Branner and Hansell 1933) placed it at 35 N, 94 W, in westcentral Arkansas. This location has been widely published in subsequent volumes of Earthquake History of the United States (for example, Heck 1938, Coffman, von Hake, and Stover 1982). However, Heinrich (1952) reevaluated the felt reports and suggested that the epicenter may have been near El Reno, Oklahoma, because of the similarity of the felt area to that of the 9 April 1952 earthquake. Docekal (1970) also reviewed the available intensity reports and concluded that the epicenter for the 1882 earthquake was not in western Arkansas or in central Oklahoma, but in northeastern Texas near the town of Paris. He assigned intensities of MMI VIII in Paris based on contemporary reports published in the U.S. Weather Bureau Monthly Weather Review (1883). However, Davis, Pennington, and Carlson (1989) discovered a mistake in the transcription of the Monthly A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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Figure 9.2. Felt area map for the Fort Gibson, Oklahoma, earthquake of 22 October 1882. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate present-day county boundaries. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989).

Weather Review account and another mistake by Docekal in interpreting the published account. In particular, Docekal assigned the epicenter to Paris based on an account of a wall being thrown down. However, the Monthly Weather Review as well as accounts in the Galveston Daily News of 24 October 1882 and the Waco Examiner of 25 October 1882 state instead that a clock was thrown from the side of a wall in Paris; this would indicate an intensity of only about MMI V. In addition, the Monthly Weather Review and Docekal both mention that a bell rang on an engine and that cotton bales swayed at Compress, Texas. This is a misinterpretation of a Dallas Weekly Herald article of 26 October 1882 that described how the earthquake was felt in Sherman, 80 km north of Dallas: At the compress it was more plainly observed than at any other point, the movement being so violent that it rang the call-bell on the engine and cotton bales on the platform were seen to sway north and south.

Evidently the compress was a factory or machine for baling cotton in Sherman and not in another city as reported by the Monthly Weather Review. The Dallas Weekly Herald article also stated that at Sherman a miller was startled by the sudden vibration of the machinery, and belts creaked as if the engine had started. The article also noted that at Bonham loose bricks were shaken from the top of 118

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a wall, consistent with a Modiﬁed Mercalli Intensity V, and that the earthquake was felt at McKinney and Greenville. Davis, Pennington, and Carlson (1989) found that the earthquake was apparently felt with greatest intensity in east-central Oklahoma (then in Indian territory); they thus concluded that the epicenter was not in Paris, Texas, but instead near the Cherokee Indian Nation settlements of Fort Gibson and Tahlequah. A report in the Tahlequah Cherokee Advocate stated: Sunday afternoon last, about four o’clock, three distinct shakes of the earth were felt at Fort Gibson, this [Tahlequah], and other places in our nation. A rumbling noise, which was distinctly heard by many, accompanied the shaking. At Fort Gibson, the trembling and vibrating were so severe as to cause door and window shutters to open and shut, hogs in pens to fall and squeal, poultry to run and hide, the tops of weeds to dip, cattle to lowe [sic], etc. etc. Immediately preceding and after the shake there was not a particle of movement, visible, in the atmosphere. Our exchanges speak of the earthquake as having been felt over a large area in the south and west. Eight or ten years ago a shock was felt in many places in this country, but it was a “wee bit” of a thing compared with that of Sunday last.

This report suggests that intensities at Fort Gibson were about MMI VIII. There were also reports that the earthquake was felt with lesser intensities in Arkansas, Kansas, and Missouri. In Arkansas, it was felt in Mount Ida, Fort Smith, Little Rock, Rogers, and Fayetteville. In Kansas it was felt in Wichita, Wellington, and Leavenworth. In Missouri the earthquake was felt at Seligman and at Warrenton, where windows rattled. The report from Warrenton is the farthest from the probable epicenter, being more than 500 km northeast of Fort Gibson. Another reason for placing the epicenter in Oklahoma is that although the earthquake was distinctly felt in Bonham, Paris, Sherman, McKinney, and Greenville, Texas, it apparently was not felt in cities farther south or east. The Dallas newspapers write only about the earthquake’s effects in Sherman, with no mention any effects in Dallas itself, only 80 km south of Sherman. The earthquake apparently was not felt in Clarksville, 40 km east of Paris, as the Clarksville Standard of 27 October 1882 whimsically noted: Nothing less than a ﬁrst-class city is entitled to an earthquake, in this region, where earthquakes are scarce. We wish it distinctly understood that one-horse towns like Clarksville set up no claims to this sort of eminence. A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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CHARLESTON, SOUTH CAROLINA — 1 SEPTEMBER 1886 Origin time: Location: Felt area: Magnitudes assigned:

02:51 UTC 32.9 N 80.0 W 5,120,000km2 mf 6.7

Stover and Coffman (1993) Stover and Coffman (1993) Bollinger (1983)

It is implausible that a local earthquake would be felt as far away as eastern Missouri and yet not be felt at cities such as Dallas and Clarksville that are so much closer to Docekal’s preferred epicenter. Other sources that mention the 1882 Fort Gibson earthquake include the Bonham Christian Messenger of 1 November 1882 and 8 November 1882, Clarksville Standard of 3 November 1882, Comanche Chief of 28 October 1882, Kaufman Sun of 27 October 1882, Comanche Peak Steam Electric System (1977), Heinrich (1941), Merriam (1956), Reagor, Stover, and Algermissen (1982), Rockwood (1883), South Texas Nuclear Project (1978), Stover and Coffman (1993), Varma (1975), and Woollard (1968). Headline

Cherokee Advocate, 27 October 1882: “Shake”

Charleston, South Carolina—1 September 1886 Roughly one week after the Charleston, South Carolina, earthquake of 1 September 1886, the Fort Worth Daily Gazette printed an article titled “Did the Fort Quake?” reporting a local shock and unusual water well activity. The article, in its entirety, reads: A gentleman of the highest veracity remarked to a GAZETTE man yesterday that he is sure he felt a slight shock about 4 o’ clock of Friday morning last, which he is now convinced was nothing more or less than a quake of old mother earth—nothing like that wrecked ill-fated Charleston, to be sure, but still a quake. Whether or not he is right in his theory is left open to conjecture, but of late a rather queer condition of several artesian wells in and about Fort Worth has been reported, which some think has a direct connection with the late terrestial [sic] disturbance. Mr. King, a well-known citizen residing near the pavillion, reports that quite recently the usually clear, pure water that comes from his well has become strongly charged with sulphur, besides being muddy. The family has now abandoned its use altogether. A gentleman named Ellison from Birdville reports almost a similar condition of his well, as have several others in various parts of the county. It is possible that the changes in the wells referred to may prove but transient; though whether they were caused by the earthquake or not is too deep a conundrum for attempted solution here.

The local shock described in the ﬁrst paragraph above occurred at about 10:00 UTC on 3 September. Nevertheless, since there was much discussion about earthquakes in the days following the Charleston event, it likely was ﬁctitious.

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PAIGE — 5 JANUARY 1887 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

17:57 UTC 30.15 N 97.06 W V–VI 4,600km2 mN 4.1

Davis and others (1989) (This study) Davis and others (1989)

However, it is possible that the Charleston earthquake did affect water wells as described. A later Fort Worth Gazette Article reported that artesian wells in the Fort Worth area were producing an unusual volume of water: A superabundance of water has been a rare cause of complaint in this droughty year, but there are a number of citizens living on East First Street in the vicinity of the river who are afﬂicted with entirely too much wetness. They claim that the ﬂow from the iceworks and the artesian wells pours out over some eight or ten acres, stagnating and producing a green scum that is not only unsightly but likely to cause sickness.

On the basis of the large area affected by the Charleston earthquake and the timing of the phenomena reported, John Armbruster (personal communication 1984) of the Lamont-Doherty Geological Observatory proposed a connection between the unusual groundwater activity and the Charleston earthquake. Other sources that mention the 1886 Charleston earthquake include Coffman, von Hake, and Stover (1982), and Mendenhall (1886). Headlines

Fort Worth Daily Gazette, 7 September 1886: “Did the Fort Quake?” Fort Worth Daily Gazette, 9 September 1886: “Too Much Water”

Paige—5 January 1887 This earthquake does not appear in published earthquake lists prior to Davis, Pennington, and Carlson (1989); however, several contemporary newspapers report that residents of Paige, Bastrop, Giddings, Elgin, and Austin felt the event. At Paige, the shock lasted two to three seconds and stopped a clock at 11:57 a.m. (17:57 UTC), recording the exact time of the earthquake. No damage was reported, but the Austin Daily Statesman noted that a wooden cistern “which had been sunk in the ground, sunk four inches lower to the bottom of the excavation cut for the cistern.” People became alarmed as dishes and pans rattled, cow bells hanging from a ceiling rang, and water pipes around the eaves of houses shook. Fifteen kilometers south of Paige the earthquake was felt and heard outside, and a tree was seen to shake. At Giddings pictures shook on walls in brick buildings, and a clock in an ofﬁce building struck violently. Glassware and dishes rattled on their shelves, and many people who felt the earthquake compared it to a light

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Figure 9.3. Felt area map for the 5 January 1887 Paige earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate present-day county boundaries. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989).

electric shock. At Bastrop the trembling lasted six seconds, and plaster reportedly fell from ceilings. Paige and the surrounding area are on the southern extension of the Mexia system of Tertiary-age normal faults. One of the major faults of that portion of the system extends between Paige and Giddings, and it is possible that the earthquake occurred along this fault. Other newspapers that mention the 1887 Paige earthquake include the Brenham Daily Banner of 7 January 1887, the Chicago Daily Tribune of 6 January 1887, and the Los Angeles Times of 6 January 1887. Headlines

Austin Daily Statesman, 6 January 1887: “Earthquake” Atlanta Constitution, 6 January 1887: “Earthquake in Texas” Atlanta Constitution, 7 January 1887: “The Texas Earthquake” Houston Daily Post, 6 January 1887: “A Genuine Earthquake Shakes Up Central Texas”

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WELLBORN — 31 JANUARY 1887 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

22:14 UTC 30.53 N 96.30 W IV local mN 3.3

Davis and others (1989) Davis and others (1989) Davis and others (1989)

SONORA, MEXICO — 3 MAY 1887 Origin time: Location: Felt area: Magnitudes assigned:

22:13 UTC 30.8 N 109.1 W 1,200,000km2 MS 7.4

Aguilera (1920) Aguilera (1920) Natali and Sbar (1982)

Wellborn—31 January 1887 Little is known about the earthquake that struck Wellborn, an east-central Texas community about 10 km southeast of Bryan–College Station. The only available details appear in the Austin Daily Statesman of 2 February 1887: Monday night, at 4:14 o’clock, the town of Wellborn, Texas, was shaken twice by slight earthquake shocks, making windows rattle and houses tremble.

The Houston Daily Post did not mention the event, and Davis, Pennington, and Carlson (1989) could not determine whether it was felt in nearby College Station or Bryan. Sonora, Mexico—3 May 1887 This large earthquake occurred in the Teras Mountains of Sonora, Mexico, and produced intensities as high as VIII to IX near the epicenter. Richter (1958) indicates that it caused severe damage in the city of Bavispe, Mexico: several roofs collapsed, the church was destroyed, and at least forty-two people were killed. Coffman, von Hake, and Stover (1982) write, “Millions of cubic feet of rock were thrown from the mountains. Cliffs of solid crystalline rock shattered as if by explosions.” The quake also was accompanied by the formation of visible faults, ﬁssures, and depressions (Aguilera 1920). The earthquake’s effects were not conﬁned to Mexico, as it damaged buildings in several Arizona cities and caused landslides in southern Arizona. However, according to the El Paso Inter-Republics of 16 May 1887, some considered these to be beneﬁcial: The landslide caused by the earthquake in the Catalina Mountains, Pima County, has uncovered a number of rich gold ledges, and prospectors are rushing out to locate them.

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The earthquake was felt as far north as Albuquerque, New Mexico, and as far east as El Paso and Fort Davis in Texas (Dutton 1905). Intensities in El Paso were probably as high as VI. The Taylor County News described the earthquake as “severe” at El Paso, and the Dallas Morning News printed an extensive story on the effects of the shock. According to the article, at El Paso the shaking rattled windows, stopped clocks, and cracked several buildings: [The motion] . . . appeared to be rather slow and regular . . . Suddenly the ﬂoor of the room seemed to rise up several inches and then settle slowly back down, the sensation being similar to that of falling a distance, accompanied with nervousness and nausea.

The earthquake also generated a great deal of panic: Brakemen paled, timid women became frightened, and children were paralyzed with fear. Out of the buildings they rushed pellmell into the streets as the ominous words, “an earthquake,” passed around . . . Business was suspended for the time and self preservation, the ﬁrst law of nature, asserted itself. Men forgot their avocations and stood awestruck and bewildered in the presence of the unseen, uncommon, and mighty force starting from whence and going where no one could know. Uneasiness as to the return of other shocks prevailed. Nothing else is talked about.

An amusing anecdote concerning the Sonoran earthquake was printed in the El Paso Times of 17 August 1931 following the 1931 Valentine earthquake. The story told of the effects of the 1887 tremor on a courtroom trial in El Paso: After the quake, it was found everybody had ﬂed from the courtroom with one interesting exception. The exception was the prisoner. He alone stayed put, although he could have escaped and been gone forever. I forget the man’s name. He was an American. Anyway, someone recited: “The boy stood on the burning deck / Whence all but him had ﬂed.” And they voted for acquittal. The defendant was freed by the earthquake and by his own inertia. But he was acquitted by an incomplete jury. W. W. Mills, brother of Gen. Anson Mills, was one of the jurors. When the earthquake came he dashed out of the building, and all the way across the river. He didn’t return to the trial.

The story may have some basis in fact. The Dallas Morning News of 4 May 1887 reported that in El Paso “ofﬁcers forgot to look after prisoners. Spectators and court in common with other mortals felt a desire to be out of doors.” 124

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EL PASO — 31 MAY 1889 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

20:00 UTC (approx.) 32.0 N 106.5 W V — mN 3.6

Davis and others (1989) Davis and others (1989) Davis and others (1989)

Finally, newspapers such as the Clarksville Standard, Dallas Morning News, and Taylor County News printed several stories about volcanoes in Mexico and Arizona in the days following the earthquake. Subsequently Aguilera (1920) suggested that large mountain ﬁres were mistaken for volcanoes and that the ﬁres may have been either coincidental or caused by friction during landslides. An article in the Taylor County News of 13 May 1887 suggests that some of the ﬁres may have existed as far east as Texas, as it states “El Paso is putting on airs because it got the ﬁrst of the western crop of volcanoes.” Other sources that mention the 1887 Sonora, Mexico, earthquake include MacDonald (1918), Northrop (1976), Staunton (1918), Sumner (1977), and Woollard (1968). Headlines

Dallas Morning News, 4 May 1887: “Shock of an Earthquake” Dallas Morning News, 5 May 1887: “The Quake at Albuquerque” Dallas Morning News, 5 May 1887: “The Earth Opens” Dallas Morning News, 6 May 1887: “Three Belching Volcanoes” El Paso Times, 17 August 1931: “Prisoner Gained Freedom during Earthquake of 1887 in El Paso”

El Paso—31 May 1889 Before Davis, Pennington, and Carlson (1989) no catalogs listed this earthquake, but it is mentioned in contemporary newspapers. The Dallas Morning News reported: An earthquake occurred at 1 o’clock today [in El Paso]. The vibration was from the southeast and lasted twenty seconds. No damage was done, but fears were entertained that the disturbance of two years ago would be repeated [this probably refers to the Sonora, Mexico, earthquake of 3 May 1887, which damaged buildings in El Paso].

The Atlanta Constitution gave a more dramatic account: A severe earthquake shock was felt here [in El Paso] yesterday afternoon. Many clerks ran out of business houses into the streets when the earth began to tremble. One building was badly cracked by the shock.

We do not know if the earthquake was felt at other locations. A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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RUSK — 8 JANUARY 1891 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

06:00 UTC (approx.) 31.7 N 95.2 W VI local mN 4.0; 3.8

Docekal (1970) Davis and others (1989) Davis and others (1989); Nuttli (1979)

Headlines

Atlanta Constitution, 2 June 1889: “Earthquake in Texas” Dallas Morning News, 1 June 1889: “Earthquake Shock”

Rusk—8 January 1891 The 1891 Rusk earthquake is one of the more interesting and debated events in the history of Texas seismicity. Several studies (Kilbourne, Lutschak, and Rice 1974; Dale 1976) have suggested that the event may have been a tornado or violent thunderstorm, as reports indicate it was felt with intensity MMI VI in Rusk but apparently not felt in the surrounding towns. However, local newspaper reports indicate that the event was probably an actual earthquake. The 1911 Catalog of Destructive Earthquakes (Milne 1911) credits an article in the London Times as its source of information for this event. The article says: Two sharp earthquake shocks were felt here [Rusk] yesterday. Chimneys were thrown to the ground and people awakened by the violence of the oscillations.

This article was apparently taken from more detailed accounts published in newspapers such as the Houston Daily Post of 9 January, the Victoria Advocate of 17 January, and the Galveston Weekly News of 15 January. An article from the Dallas Morning News (reprinted in Carlson 1984) mentions “a few parties here who experienced the Charleston shocks of 1887 pronounced the phenomenon last night a genuine earthquake.” Newspaper reports indicate the shock was not felt in towns other than Rusk. The Jacksonville Banner, the Rusk County News in Henderson, the Crockett Weekly Courier, and the Marshall Daily Messenger all carried the story but did not mention anyone other than in Rusk who felt the earthquake; in fact, some of the newspapers treated the story with levity or disbelief. There are no accounts of the event from Rusk newspapers because a ﬁre in the early 1930s destroyed a warehouse containing all of the previous issues (Dale 1974). Are the suggestions plausible that the Rusk event was not an earthquake but was the result of a violent thunderstorm? It is true that there were reports of damaging storms on the night of 7 January in Yoakum and Hallettsville, towns approximately 320 km southwest of Rusk. However, according to the Dallas Morning News: 126

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During these [earthquake] disturbances there was no wind [emphasis added] though there was a slight rainfall and some electrical force prevailing, but not of sufﬁcient strength to produce the shock.

Although no atmospheric disturbance seems to have happened at the time, the small felt area of the Rusk event does not preclude the possibility that it was indeed a shallow-focus earthquake. Furthermore, tornadoes usually tear off roofs rather than level chimneys. And Rusk does lie along the Mount Enterprise Fault Zone (see ﬁgure 2.6), which occasionally does generate small but genuine earthquakes (see descriptions of 19 March 1957 and 6 November 1981 earthquakes). Other earthquakes have had similarly small felt areas. For example, two shallow-focus earthquakes (0 –5 km depth) that occurred on 14 August 1965 in extreme southern Illinois had mb equal to 3.2 and 3.8 and felt areas of 200 km2 and 700 km2, respectively (Nuttli and Zollweg 1974). The larger event was not felt in any towns at distances exceeding 40 km from the epicenter, but it had a magnitude similar to that of the Rusk event. The Fashing, Texas, earthquake of 23 July 1983 with mbLg of 3.4 and MMI of V had a felt area of no more than 200 km2. Thus it is quite possible that a shallow-focus earthquake centered near Rusk could be felt strongly in that town and not in the neighboring communities. Other sources that mention the 1891 Rusk event include Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), Sheets (1947), South Texas Nuclear Project (1978), Stover and Coffman (1993), and Varma (1975). Headlines

Dallas Morning News, 9 January 1891: “Rusk Shaken Up” London Times, 10 January 1891: “Earthquake Shocks in Texas”

Uvalde—31 August 1894 (Flood, probable spurious earthquake report) The Fort Worth Gazette of 1 September 1894 ran a story on its front page with a long and dramatic headline: “Leona River Flood. Hundreds of Miles of Territory Underwater. Appalling Loss of Life. Millions of Dollars Worth of Property Gone. Result of an Earthquake.” The article begins by describing ﬂoods from two days of “unprecedented rains” and then continues: A tidal wave came down the Leona River and partially submerged this town early yesterday morning. An earthquake shock was felt a few minutes before. The ﬂood that came down upon the town is believed to be the result of a peculiar phenomena [sic]. The ﬁssures in the ground caused by the earthquake are believed to have tapped the A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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large artesian water basin in the hills, thus swelling from nature’s reservoir the already swollen basin of the Leona River into a tidal wave. It was 2 o’clock in the morning and the inhabitants of the town were sleeping. All of the houses on the east side of town were submerged, and in the darkness and through the downpour of the rain that was falling could be heard the cries of distress from the ill-fated inhabitants in their wild efforts to save their lives and those of their families and loved ones.

The article then continues with tales of heroic efforts and escapes and lists the names of those thought to have drowned. The Chicago Daily Tribune published a similar but shorter story on the same day, repeating some of the text but adding: An earthquake shock of some seconds duration was distinctly felt during the night. At one place near the city a quarter of a mile of heavy cracks appear on each side of the Leona River, having apparently no bottom.

When the weekly Beeville Bee came out on 7 September the reporters compared the Texas disaster to wildﬁres in Minnesota: Texas had her ﬂood and earthquake, but it remained for Minnesota to be the scene of the most terrible and devastating catastrophe that has visited the United States in years. The wires were still coming in with messages describing the destruction and loss of life by ﬂoods and an earthquake at Uvalde and surrounding country when the news ﬂashed from sea to sea, from Canada to the Gulf, that whole towns in Minnesota have been swept out of existence by forest ﬁres, and with them their inhabitants.

In spite of the references to an earthquake in several papers, we conclude that the disaster described was no more than a sudden ﬂood, caused by intense rains and perhaps accompanied by the bursting of a dam or logjam or, as the newspaper suggested, the breaching of a water basin. The rumbling felt and heard by some may very well have been no more than thunder or the rushing onslaught of ﬂoodwaters, and the large cracks observed at the river’s edge the result of slumping from the rain and ﬂood. The Dallas Morning News described the events at Uvalde but made no mention of an earthquake; rather, it attributed the ﬂooding simply to a cloudburst. At the time of the Uvalde disaster most of South and East Texas were experiencing unusually intense rains and ﬂooding. The Brenham Daily Banner (31 August and 1 September 1894) describes nearly nonstop downpours in one of the heaviest rains of the seasons, accompanied by “wind and lightning and heavy thunder.” Likewise, the Fort Worth Gazette article describes massive ﬂooding in several river valleys with bridges and other structures being washed away at places other than Uvalde. 128

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CREEDMOOR — 9 OCTOBER 1902 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

19:00 UTC (approx.) 30.10 N 97.60 W IV–V 5,600km2 mN 3.9

Davis and others (1989) Davis and others (1989) (This study) Davis and others (1989)

Headlines

Dallas Morning News, 1 September 1894: “A Sea from the Sky” Fort Worth Gazette, 1 September 1894: “Leona River Flood”

Creedmoor—9 October 1902 This earthquake was centered approximately 15 km southeast of Austin near the small town of Creedmoor and was felt in Austin, Bluff Springs, Creedmoor, Buda, Garﬁeld, Red Rock, Bastrop, and possibly La Grange. The Austin Daily Statesman stated that many residents of communities south and southeast of Austin heard two noises in quick succession, likened to cannon blasts, and became alarmed; one man at Creedmoor “became so frightened that he jumped into a creek and nearly drowned before he was hauled out.” Residents in Red Rock and Bastrop also were greatly disturbed. An article in the Nacogdoches Daily Sentinel of 14 October 1902 suggests that the shock may have been felt as far away as La Grange, 74 km southeast of the epicenter. The article, in its entirety, reads: Grand old Texas, determined to diversify her crops until criticism is silenced, is now producing earthquakes. Slight shocks of that character are reported to have occurred at LaGrange and other places a few nights ago.

The article probably refers to the 9 October event, despite the fact the shock occurred in the early afternoon rather than at night. This earthquake caused quite a commotion among the people of Austin and surrounding communities, and there was much speculation concerning the cause of the tremor. For quotes from some rather colorful stories published about this earthquake in the San Antonio Daily Express and the Austin Daily Statesman, see the discussion in chapter 2. Other newspapers that mention this earthquake include the Bastrop Advertiser of 11 October 1902 and the Devine News of 16 October 1902. Headlines

Austin Daily Statesman, 10 October 1902: “People Awe-Stricken by Trembling of the Earth” San Antonio Daily Express, 11 October 1902: “Puzzled by Shock” San Antonio Daily Express, 12 October 1902: “Shock Caused by Meteor” A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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Figure 9.4. Felt area map for the 9 October 1902 Creedmoor earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate present-day county boundaries. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989).

Socorro, New Mexico—1906 A swarm of earthquakes that occurred near Socorro, New Mexico, during 1906 and 1907 included three 1906 shocks that Reid (1911) reported as felt in El Paso, Texas. We have found no details about the felt effects, except that the intensity in El Paso was approximately MMI III for the 12 July and 15 November events and MMI III–IV for the 16 July event. Other sources that mention these earthquakes include Davis, Pennington, and Carlson (1989), Northrop (1976), Sanford, Olsen, and Jaksha (1981), Stover, Reagor, and Algermissen (1983), and Woollard (1968). Amarillo—April 1907 (Possibly spurious) The Amarillo Daily News of 31 July 1925 mentioned an earthquake in 1907: Mrs. C. R. Warren, 1101 Lincoln street, declared a temblor hit Amarillo about 6 o’clock one Saturday afternoon in April, 1907, breaking a window in her home. People living along Madison Street said it shook their dishes. 130

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SOCORRO, NEW MEXICO — 1906 Dates:

Origin times:

Location:

(a) 12 July 1906 (b) 16 July 1906 (c) 15 November 1906 (a) 12:15 UTC (b) 19:00 UTC (c) 12:15 UTC 34.0 N 107.0 W

Coffman and others (1982)

AMARILLO — APRIL 1907 (POSSIBLY SPURIOUS) Origin time: Locations: Maximum intensity: Felt area: Magnitudes assigned:

00:00 UTC (approx.) 35.2 N 101.8 W 35.5 N 101.2 W V — mN 3.6; 3.0

Northrop and Sanford (1972) Nuttli (1979) Northrop and Sanford (1972) Davis and others (1989); Nuttli (1979)

Udden (1926) notes that a virtually identical passage appeared in the Panhandle Daily News. No earlier reference to this event has been found, thus creating an eighteen-year gap between the date of the event and the earliest report. Northrop and Sanford’s (1972) location is consistent with the Lincoln and Madison Streets area of Amarillo; however, the other location is well to the east of Amarillo, and it is unclear why it was assigned there. Other sources that mention this event include Comanche Peak Steam Electric System (1977), Nuttli and Herrmann (1978), Pantex Facility (1975), and Reagor, Stover, and Algermissen (1982). An investigation of contemporary Amarillo newspapers has uncovered no evidence that the 1907 earthquake ever occurred. Perez (2001) reread microﬁlmed copies of the Twice a Week Harold and the Weekly Harold that covered much of 1906 and nearly all of 1907. She found no mention of any Panhandle earthquakes, although she found seventeen articles that mentioned earthquakes elsewhere, including Asia, Chile, El Paso, Jamaica, Mexico, Prussia, and Russia. An article from the Associated Press appearing in the Weekly Harold mentions reports from Galveston that indicate Texas oil ﬁeld production decreased by 45 percent following an earthquake in Jamaica. The number and variety of these articles suggest that had an earthquake occurred in Amarillo, it would have been reported in the newspapers. It is possible the reports of the alleged 1907 earthquake are describing a nearby explosion, or they may be garbled felt reports from the 1917 Panhandle earthquake. As described later, there is confusion about the exact date for the 1917 earthquake. If 28 March is correct, it occurred on a Wednesday, while the 1926 Amarillo Daily News article reports its occurrence as 24 March, which is a Saturday. A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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HEMPSTEAD — 8 MAY 1910 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

17:30 UTC 30.1 N 96.0 W IV 2,900km2 mN 3.8; 3.8

Docekal (1970) Docekal (1970) (This study) Davis and others (1989); Nuttli (1979)

Headline

Weekly Harold, 31 January 1907: “A Curious Phenomena— Oil Fields in Texas Cease to Yield since the Jamaica Earthquake”

Hempstead—8 May 1910 Residents of the towns of Hempstead, Brenham, Navasota, and San Felipe reported hearing and feeling this Sunday morning tremor. Articles in both the Houston Post and Houston Chronicle stated that the “roar” lasted for ﬁve seconds. In Hempstead several persons stated that windows in their homes rattled so loudly that they could be heard in other rooms. A large congregation at the Baptist church in Hempstead also felt the shock, and people who lived 25 km away in the country reported that they “noticed the shock, but could not tell if it was from above or below.” The article in the Houston Chronicle stated that: A reliable man of this town [Bellville] who was some distance out at the time stated to the Chronicle correspondent that it seemed to him that the noise was not like that of an earthquake, but could be heard up in the air at a height of six or eight feet.

Several published earthquake lists also mention an earthquake with the same intensity, felt area, and epicentral location that occurred three days later on 11 May. The main historical references for this second earthquake are the unpublished notebooks, scrapbooks, and card ﬁles of a contemporary seismologist, Harry F. Reid. Searches of local newspapers found no mention of the 11 May event, except for this short article published in the 12 May edition of the Navasota Examiner-Review, a weekly newspaper: Yesterday morning at 11:20 a loud explosion occurred—about like a big blast of dynamite, though inquiry in the afternoon and today failed to locate the reason for it. A number of people heard the report but none have accounted for it. Wonder if Halley’s Comet is responsible for it.

Because the paper was published on 12 May, the reporter’s statement would make it appear that the event occurred on 11 May, the day of the purported second earthquake. However, on page 8 of the same edition, the following article appears: We note in the Houston Post of today that the correspondent at Hempstead speaks of the same report heard here at 11:20 on Sunday, and reported in our columns on Mon132

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Figure 9.5. Felt area map for the 8 May 1910 Hempstead earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate presentday county boundaries. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989).

day. Also at San Felipe, some forty miles from Hempstead, the report and shock accompanying it was [sic] both heard and felt by many. The mystery is still unsolved.

The two articles undoubtedly refer to the same event because of the similarity of times. Apparently, the ﬁrst article was written on 9 May and published along with the second article on 12 May, without clarifying what day “yesterday” was. Reid may have seen only the ﬁrst of the two articles and thus concluded incorrectly that a second earthquake had occurred. Other sources that mention the A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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ANDERSON — 30 DECEMBER 1914 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

01:00 UTC (approx.) 30.5 N 95.9 W IV — mN 3.3; 3.5

von Hake and Cloud (1971) Humphreys (1915) Davis and others (1989); Nuttli (1979)

1910 Hempstead earthquake include Comanche Peak Steam Electric System (1977), Reagor, Stover, and Algermissen (1982), South Texas Nuclear Project (1978), Varma (1975), and Woollard (1968). Headlines

Houston Chronicle, 12 May 1910: “Heard Strange Noise” Houston Post, 11 May 1910: “Hempstead Felt Earthshock”

Anderson—30 December 1914 The only available information about this earthquake is from the Monthly Weather Review (Humphreys 1915), which reports that at 7:00 p.m. local time on 29 December one shock occurred, lasting a few seconds and accompanied by rumbling sounds. The Review lists it as a possible explosion, with no further details. We have not uncovered any newspapers reporting the shock. The South Texas Nuclear Project (1978) Final Safety Analysis Report did note: The Victoria Advocate of December 30, 1914, published an article, “Two Boys Smothered to Death by Landslide.” A landslide occurred along the west bank of the Guadalupe River at 4:45 p.m. on December 29.

Because the times of the earthquake and the landslide differ by two hours, the events are probably unrelated. Other sources that mention the 1914 Anderson earthquake include Comanche Peak Steam Electric System (1977), Docekal (1970), Reagor, Stover, and Algermissen (1982), Varma (1975), and Woollard (1968). Panhandle—28 March 1917 This event has one of the most puzzling and convoluted histories of all the Texas earthquakes. Various sources list the date of occurrence as 28 January, 24 March, 27 March, and 28 March; the origin time is either 19:30, 19:56, or 19:57 UTC. The 28 January date is from the Dispatches of Earthquakes of Georgetown University (Tondorf 1917). The 24 March date ﬁrst appears after the 30 July 1925 Panhandle earthquake in articles appearing in The Amarillo Daily News and the Panhandle Herald. The 27 March listing may have come from Pratt (1926), who does not list his source of information but describes a “rather severe shock at the town of Panhandle and in the territory immediately adjacent on 27 March 1917, at 1:56 p.m. [19:56 UTC].” The original source for the 28 March date was the 134

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PANHANDLE—28 MARCH 1917 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

19:56 UTC 35.4 N 101.3 W Vl 7,600km2 mN 3.9 mN 3.2, 4.2, 4.7

Woollard (1968) Humphreys (1917) (This study) Davis and others (1989) Nuttli (1979)

Monthly Weather Review (Humphreys 1917), which notes that two observers in the city of Panhandle, Texas, each reported two shocks at 19:56 UTC. Finally, Docekal (1970) lists an aftershock for this event at 17:38 CST (23:38 UTC); however, we examined all of Docekal’s listed sources but found no reference to an event at this time. Nuttli also lists this aftershock but gave 27 March as the date and assigned a magnitude mN of 3.0. Unfortunately, we have been unable to locate contemporary newspapers from the Texas Panhandle to ﬁx the date. Northrop and Sanford (1972) discussed the uncertainty in the date and preferred 24 March on the basis of the 1925 newspaper reports. However, they apparently were unaware of either the Georgetown Dispatches or the Monthly Weather Review. The January date in the Dispatches may be a mistake, as all other original sources list March as the month of the event. The only other source from 1917 is the Monthly Weather Review, which lists 28 March as the date of occurrence. As the 24 March and 27 March listings both made their ﬁrst appearance in publications several years after the earthquake, the most likely date is probably 28 March. In addition, the Monthly Weather Review lists some phases from the seismograph at the University of Kansas in Lawrence, Kansas, that are consistent with the occurrence of an earthquake in the Texas Panhandle at approximately 19:56 UTC on 28 March.2 Another possibility is that two or more earthquakes occurred on different dates. However, this is unlikely since none of the original sources lists more than one date and since all mention the same approximate origin time. There are also conﬂicting reports about the extent of the felt area. The 1925 Amarillo Daily News story lists the shock as “felt throughout the Panhandle.” In contrast, Pratt (1926) describes the shock as felt in the city of Panhandle and the area surrounding it but not felt in Amarillo or Pampa. However, an article in the Amarillo Daily News of 12 March 1948 indicates that the shock was felt in Amarillo: Mrs. Abrahamson recalled another temblor in Amarillo about 1916. She said the dishes rattled on the table and she noticed a pull-type light switch swinging.

Of course, this could be a reference to another shock such as the 1925 event, felt in Amarillo. Finally, Udden (1926) states that the Panhandle Herald reported the A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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Figure 9.6. Felt reports for the 28 March 1917 Panhandle earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Map and intensity information are revised using information reported by Davis, Pennington, and Carlson (1989).

1917 shock as “distinctly felt” in northern Carson County and southern Hutchinson County. The intensity in the town of Panhandle itself may have been quite high. Although the Dispatches of Earthquakes from Georgetown only reported the shock as “sensible,” the Monthly Weather Review stated the shock “caused considerable alarm” and that “plaster cracked.” The 1925 press reports also suggest a high intensity. Udden (1926) quoted from an article in the Panhandle Herald: At the time particles of the ceiling plaster of the Panhandle bank were shaken loose and fell to the ﬂoor.

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EL PASO—7 MARCH 1923 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

05:03 UTC 31.8 N 106.5 W VI 200,000km2 mN 4.7; 4.5

Docekal (1970) Davis and others (1989) Davis and others (1989) Davis and others (1989); Nuttli (1979)

Also, the Amarillo Daily News of 31 July 1925 noted: Cement on the walls of many buildings was cracked, and the school building was severely shaken. However, it suffered no damage. The children became excited, and school was dismissed at once. People who were riding in cars at the time declared they could hardly remain in their seats due to the intensity of the shock.

Most later catalogs interpreted the maximum intensity as Vl; this appears to be a reasonable estimate based on these reports. Other sources that mention the 1917 Panhandle earthquake include Coffman, von Hake, and Stover (1982), Coffman and von Hake (1973b), Comanche Peak Steam Electric System (1977), Nuttli and Herrmann (1978), Pantex Facility (1975), Reagor, Stover, and Algermissen (1982), Sellards (1939), Stover and Coffman (1993), and von Hake (1977). El Paso—7 March 1923 At 10:05 p.m. on 6 March 1923 (05:03 UTC on 7 March), an earthquake occurred that had its strongest effects in El Paso, Texas, and in nearby Juarez, Mexico. At Juarez the earthquake collapsed an adobe structure and killed a man. According to the Houston Post: Juan Ortiz, a Mexican tenant farmer who lived six miles from Juarez, suffocated when his adobe house caved in during the quake, it was announced at the Juarez hospital, where the body was taken.

This is the only known instance of a Texas earthquake resulting in a human death. It is possible that the epicenter was actually in northern Mexico, as Sanford and Toppozada (1974) noted that “newspaper accounts suggest an epicenter in northern Chihuahua.” This is consistent with reports in the Houston Post, which noted that “a few windows were broken and bottles in Juarez were disturbed, but no big damage resulted,” while in El Paso it only rattled dishes and was “felt by many.” A seismograph at Tucson, Arizona, recorded an event beginning at 05:02:58 UTC that possessed an S-P time of thirty-ﬁve seconds, suggesting an epicenter about 330 km distant (see chapter 1). The limits of the felt area are also uncertain. Southeast of El Paso, residents of Sierra Blanca, Texas, felt two faint shocks; to the west the earthquake was “felt by several” in Columbus, New Mexico; to the north it was felt clearly by

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Figure 9.7. West Texas towns mentioned in this compendium, and felt reports for the 7 March 1923 earthquake near El Paso. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Map and intensity information are revised using information reported by Davis, Pennington, and Carlson (1989).

residents of Alamogordo, New Mexico. However, the Wichita Daily Times reported that “slight tremors were felt in Mexico as far as 200 miles [320 km] south of Juarez.” And the Houston Post stated that the earthquake was felt in Phoenix, Arizona, about 500 km from El Paso. Other sources that mention this 1923 El Paso earthquake include Humphreys (1923), Comanche Peak Steam Electric System (1977), Reagor, Stover, and Algermissen (1982), Seismological Notes (1923), and Woollard (1968). Headlines

Houston Post, 8 March 1923: “El Paso Quake Fails to Return” Wichita Daily Times, 7 March 1923: “Mexican Suffocates When House Caved in by Quake”

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SILVERTON—29 JULY 1925 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

11:30 UTC 34.5 N 101.2 W IV — mN 3.3 mN 3.8

Docekal (1970) Docekal (1970) Davis and others (1989) Nuttli (1979)

Goose Creek—1925 In the mid-1920s several small earthquakes were reported near the Goose Creek oil ﬁeld along San Jacinto Bay east of Houston. Exact dates are unknown; Yerkes and Castle (1976) state only that there was activity in 1925 but do not indicate a month or day. Contemporary descriptions of the tremors (Pratt and Johnson 1926) note that they “shook the houses, displaced dishes, spilled water, and disturbed the inhabitants generally.” This suggests intensities of MMI III–IV. These events have been attributed to ground subsidence resulting from the removal of more than 100 million barrels of oil from Goose Creek ﬁeld. Heavy production started in this ﬁeld in 1916 (Minor 1925), and by 1918 Gaillard Peninsula and other nearby lowlands near the center of the ﬁeld had subsided below sea level. By 1926 total subsidence in the central portion of the ﬁeld had reached more than 3 feet. Several fractures with offsets as great as 16 inches appeared along the outer edges of the ﬁeld; some of the movements along the fractures occurred overnight and were apparently accompanied by small earthquakes. Other sources that mention the 1925 Goose Creek earthquakes include Davis, Pennington, and Carlson (1989), Sellards (1930b), and Sheets (1947). Silverton—29 July 1925 This earthquake allegedly occurred about twenty-ﬁve hours prior to the large 30 July 1925 Panhandle earthquake and may have been a foreshock of that event. The only felt report comes from Silverton (about 100 km from the epicenter of the main shock). Several published descriptions (Neumann 1926a and 1926b; Docekal 1970) all state that: Silverton, Texas, reported the ground bumped and trembled for 10 seconds; sounds like thunder were heard, and objects within houses rattled.

It is possible the Silverton event was merely a felt report of the Panhandle earthquake, with an erroneous date and hour given. The date is one day off, and the hour is almost exactly one hour before the time of the Panhandle event (about 12:17 UTC). Another point in favor of this hypothesis is that no felt report exists for the main shock at Silverton, where an intensity IV–V would be

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TEXAS PANHANDLE REGION—30 JULY 1925 FORESHOCKS Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

Possibly several, 06:00 –11:00 UTC Scattered reports IV — mN 4.2

Davis and others (1989) Nuttli (1979)

expected on the basis of reports of nearby cities. Other sources that mention the 1925 Silverton event include Comanche Peak Steam Electric System (1977), Nuttli and Hermann (1978), and Reagor, Stover, and Algermissen (1982). Texas Panhandle Region—30 July 1925 Foreshocks Many sources have suggested that one or more foreshocks occurred during the early morning hours prior to the Panhandle event of 12:17 UTC on 30 July 1925. Contemporary newspapers provide support for this assertion. The Wichita Daily Times reports a shock at Childress around 2:00 a.m. (08:00 UTC), whereas the Dallas Morning News indicates a “very light” shock at Hobart occurring at 4:00 a.m. (10:00 UTC). The Cleburne Times mentions a 2:00 CST (08:00 UTC) shock at Panhandle, Texas, and a report from Post, Texas, city engineer notes: I found several that experienced the early morning shocks (about 2 a.m.), the most severe of the two, and quite a number of the other (about 6 a.m.) the main shock [at 12:17 UTC], this latter being hardly more than a mere tremor. Those of us who experienced the ﬁrst, agree that there were a series of ﬁve to seven tremors in quick succession covering a period of perhaps a second of time and perceptibly shaking the houses as severely as does [sic] some of the winds we have in this section. One man occupying a stone house felt it just as perceptibly as others of us occupying frame houses.

The Amarillo Daily News of 31 July 1925 also mentions the possibility of earlier shocks: Now that the earthquake shocks have been felt, some of the “wise” ones are saying that there were tremors at midnight and also at 5 o’clock in the morning.

Several points concerning these events make them difﬁcult to catalog: 1. The times reported may be inaccurate because they originate in the middle of the night. Most of the reports may be from a single foreshock to the 12:17 UTC event; 2. If the tremors are related to the 12:17 UTC event, it is unclear why the earlier shock was felt more strongly than the main shock at Post; 3. It is difﬁcult to understand why such low intensities were felt at widely separated locations, with no reports from other cities.

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Figure 9.8. Panhandle towns mentioned in this compendium, and cities reporting shocks the night before the 30 July 1925 earthquake. Dashed lines indicate county boundaries; the Roman numerals indicate the Modified Mercalli Intensities reported at Amarillo, Childress, Hobart, Panhandle, and Post. Town labeled “WD” is White Deer.

Thus although one or more shocks almost certainly occurred during the night, it is not possible to conﬁdently assign a single time or location. Other sources that mention the 1925 Panhandle foreshocks include Comanche Peak Steam Electric System (1977), Neumann (1926a and 1926b), Northrop and Sanford (1972), Nuttli and Herrmann (1978), Pantex Facility (1975), Reagor, Stover, and Algermissen (1982), Shurbet (1969), and Udden (1926). Panhandle—30 July 1925 This is the ﬁrst large and widely felt earthquake known within the Texas Panhandle. It occurred shortly after 6:00 a.m. local time, awakening and alarming people in numerous Panhandle towns. The strongest shaking occurred within a roughly elliptical area centered between the towns of White Deer and Cuyler to

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PANHANDLE—30 JULY 1925 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

12:17 UTC 35.4 N 101.3 W VI 520,000km2 mN 5.4; 4.8 m0.4Hz 5.5

Docekal (1970) Docekal (1970) (This study) Davis and others (1989); Nuttli (1979) Pantex Facility (1975)

the south and Plemons to the north. The Amarillo Daily News reports that at White Deer buildings rocked, sleepers were “suddenly roused from their beds,” and the citizens were “greatly alarmed.” Nearby at Pampa the shock was “very severe . . . People awakening could hardly realize what had happened. Pampa people ran from their houses and excitement was widespread.” Groceries fell from shelves at Groom, while at Canyon people sleeping were “shocked wide awake,” and tables shook enough to mix cups and plates. At Clarendon, Pratt (1926) states that “people were so disturbed as to run from their houses in spite of a heavy fall of rain.” In Amarillo, Udden (1926) noted that the earthquake caused so much concern that within three hours of the event one insurance company alone had written eight earthquake insurance policies. In spite of the severity and expanse of the shaking, the earthquake caused only minor damage. The Amarillo Daily News reported that in Panhandle a bin broke and about two tons of coal spilled. At Cuyler, Pratt (1926) states that “a vase was overturned and milk crocks spilled their contents” and that “it was necessary to do considerable work on the [Santa Fe Railroad] track, which he [the roadmaster] thought might have been due to settling by the earthquake.” At Plemons, Texas, “plaster fell, and jars were displaced from shelves.” Plaster also fell in Guymon, Oklahoma, and plaster walls cracked in Amarillo. In Dillon, New Mexico, the shock badly damaged a large cistern. In Tulia, Texas, one man claimed the wallpaper in his house cracked. Contemporary accounts suggest uncertainty about the true origin of some of the reported damage. In Wichita Falls there was a report of a fallen chimney; however, the Wichita Falls News noted that “although news reporters located the fallen chimney and veriﬁed the report that it fell about the same time that the earthquake quaked, the statement . . . should be taken with the proverbial grain of salt.” A church in Wellington and a service station in Clarendon also suffered, although in both cases the Amarillo Daily News suggested that soil consolidation in response to heavy rain may have caused the damage. Pratt (1926) discussed reports that the earthquake affected the ﬂow of Panhandle oil wells: “Some wells were said to have been sheared off, others ceased to ﬂow, and still others increased their ﬂow.” However, he could ﬁnd no evidence supporting the rumors. The Clovis Journal reported an immense system of deep ﬁssures near the town of Mountainair, New Mexico. However, the ﬁssures were not discov142

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Figure 9.9. Felt area map for the 30 July 1925 Panhandle earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded regions indicate major oil (dark shading) or gas (light shading) fields as mapped by Galloway and others (1983) and Kosters and others (1989) that were established prior to 1925. Labeled cities include only those not indicated in figure 9.8. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989).

ered until 2 August, and considering they were 460 km from the epicenter it seems highly unlikely that the Panhandle earthquake caused them. Several sources provide additional detail concerning the nature and geographical extent of the felt effects from this earthquake (Neumann 1926a; Udden 1926), including three investigations that produced isoseismal maps (Udden 1926; Docekal 1970; Davis, Pennington, and Carlson 1989). All ﬁnd that a large part of the Texas Panhandle falls within the intensity V zone. In Texas the intensity IV zone extends south at least to Floydada; the intensity III reports include cities as far away as Wichita Falls, 310 km to the southeast. In Post, 250 km to the south, “quite a number” of people felt what was “hardly more than a tremor.” The western boundary of the shock extended at least as far west as Mountainair, New Mexico, 370 km away. There is considerable discrepancy concerning the number, duration, and timing of shocks. The majority of investigations report that three shocks were felt A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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over a period of ﬁfteen seconds at 12:17 UTC (Pratt 1926; Docekal 1970; von Hake 1977; Coffman, von Hake, and Stover 1982). However, Reagor, Stover, and Algermissen (1982) list three shocks at 12:17, 12:22, and 12:27 UTC; since their source is Coffman, von Hake, and Stover (1982), probably they have misread “15 seconds” as “15 minutes.” Nevertheless, evidence indicates that other shocks may have occurred. Udden (1926) reviews newspaper clippings indicating that Leavenworth, Kansas, experienced a weak shock at 12:00 UTC and a stronger one at 12:15 UTC, and that Clarendon, Texas, experienced “two sharp earthquake shocks felt at 6:05 and 6:10 a.m. [12:05 and 12:10 UTC].” However, Neumann (1926a) lists two shocks there at 12:15 UTC. There is also little agreement as to the time of the main shock. Neumann (1926a) and Davis, Pennington, and Carlson (1989) summarize the various times reported; the thirty-three reported times include ten different minutes between 12:00 and 12:40 UTC on 30 July, although twenty-two of these reports indicate that the main shock occurred at 12:15 or 12:17 UTC. Probably the wide time spread reﬂects the fact that local timing errors were quite large in 1925. Volcanoes, oil extraction, and deeply buried faults were all suggested as the cause of the earthquake. The Amarillo Daily News said: Mount Capulin, the best preserved extinct volcano crater on the western hemisphere near Deadman, New Mexico, is about 150 miles northwest of Amarillo and many suggested that this was an indication there were internal volcanoes which were erupting, thus causing the earthquake here.

For quotes from Pratt (1926) and Coffman, von Hake, and Stover (1982) suggesting the earthquake might be induced by petroleum production (see the discussion in chapter 2). Other sources that mention this earthquake include Wichita Daily Times of 30 July 1925, Comanche Peak Steam Electric System (1977), Heinrich (1941), Merriam (1956), Neumann (1926b and 1926c), Northrop and Sanford (1972), Nuttli and Herrmann (1978), Seismological Notes (1925), and Stover and Coffman (1993). Headlines

Amarillo Daily News, 31 July 1925: “Entire Panhandle Rocked by Quake, No Damage Done” Amarillo Daily News, 31 July 1925: “Oil Geologists Say Structure Cause of Earthquake” Amarillo Daily News, 31 July 1925: “Quakeitis” 144

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WHITE DEER—31 JULY 1925 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

18:00 UTC (approx.) 35.5 N 101.1 W III local mN 3.0

Davis and others (1989) Davis and others (1989) Davis and others (1989)

MEXICO—1 NOVEMBER 1928 Origin time: Location:

04:16 UTC 26.0 N 106.0 W

Heck and Bodle (1930)

Crosbyton Review, 7 August 1925: “Earthquake Tremors Felt Early This Morning over Panhandle of Texas” Hereford Brand, 30 July 1925: “Report that Slight Earthquake Tremors Are Felt Here and at Other Panhandle Points Thursday Morning” Norman Transcript, 30 July 1925: “No Damage Caused but Hundreds Badly Frightened” Lubbock Plains Journal, 6 August 1925: “Geologists Believe Earthquake Came as a Structural Result” Lubbock Plains Journal, 30 July 1925: “Earth Tremors Are Felt Here Thursday” Randall County News, 30 July 1925: “Earthquake is Felt in Canyon 6:15 a.m.” Terry County Herald, 7 August 1925: “No One Felt Earth Quake Here Believed” Texas Spur, 31 July 1925: “Earthquake Tremors Felt in Spur Thursday”

White Deer—31 July 1925 A contemporary study (Pratt 1926) of the Panhandle earthquake notes, “At White Deer, a minor shock was felt about noon of the day following the main earthquake; no one outside of White Deer appears to have been aware of this second shock.” White Deer is very close to the epicenter of the Panhandle event, and it seems probable that the “minor shock” felt was an aftershock. We haven’t found this tremor listed in any other catalogs. Mexico—1 November 1928 Citizens of several towns in West Texas felt this Mexican earthquake, which occurred at 9:16 p.m. local time on Halloween night. The El Paso Times reported that in El Paso the earthquake shook houses and furniture, rattled windows, swayed overhead lights, and stopped clocks; people were thrown into a “semipanic” by the tremor, and hundreds of calls were made to the El Paso Times and to local sheriff and police departments. One resident of El Paso claimed that “the A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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BIG SPRING—18 TO 19 OCTOBER 1929 (SEISMIC EXPLORATION BLASTING) Origin time: Location: Maximum intensity: Felt area:

Various, a.m. 31.9 N 101.7 W V Up to 5,000km2

Davis and others (1989) Davis and others (1989) Davis and others (1989)

shock was so strong that it shook his chickens from their roosts.” The Pecos Enterprise and Gusher reported that in Pecos the earthquake shook houses and lights, although several thought at ﬁrst that the shaking was a Halloween prank. The tremor stopped clocks in Valentine, Texas, and was felt at Canutillo, about 6 km north of El Paso. No damage was reported in Texas. Other sources that mention this earthquake include Coffman, von Hake, and Stover (1982), Davis, Pennington, and Carlson (1989), and Comanche Peak Steam Electric System (1977). Headlines

Atlanta Constitution, 1 November 1928: “El Paso Shaken by Earthquake Without Damage” El Paso Times, 1 November 1928: “Quake Shakes El Paso Homes” Pecos Enterprise and Gusher, 2 November 1928: “Baby Quake or Just Spooks Fret Pecos”

Big Spring—18 to 19 October 1929 (Seismic exploration blasting) The Wichita Daily Times reported that between midnight and 7 a.m. (local time) on the morning of 18 October 1929, ﬁve shocks awakened several residents of Big Spring. The last shock was the largest of the series. An initial check with oil companies failed to reveal any blasting, and the events were assumed to be a small series of earthquakes. Sellards (1930a) notes similar tremors on the morning of 19 October. He reports that residents of several towns felt both series of shocks: One person at Big Springs [sic] states that he was awakened about 3 a.m. [local time on the morning of 18 October] by what he thought was an automobile hitting the house in which he was sleeping. Another says he was awakened about this time thinking some one was rattling his door. At one place in Stanton a lamp chimney was broken, and at another the glass in a door was fractured . . . [Both nights] the tremors were felt at Sterling City forty-four miles east [of the source]; at Big Springs [sic] thirty-two miles northeast; at Knott forty miles north; at Stanton twenty miles north; and at Midland twenty-one miles northwest. Inquiry among farmers and ranchmen indicated that even beyond the towns mentioned the tremors were more or less distinctly felt.

Sellard’s investigation determined that dynamite blasting for seismic exploration was responsible for the tremors. Several charges of dynamite were ex146

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VALENTINE—16 AUGUST 1931 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

11:40:22 UTC 30.69 N 104.57 W VIII 1,000,000km2 mN 6.0 mN 5.6 mN 5.6 –5.9; Mw 6.3 mf 6.4 MS 6.4

Dumas and others (1980) Neumann (1932) Davis and others (1989) Davis and others (1989) Nuttli (1979) Dumas and others (1980); Doser (1987) Sanford and Toppozada (1974) Gutenberg and Richter (1949)

ploded during the early morning hours of October 18 and 19 from a location 23 km west of Garden City in Glasscock County. The times of the largest blasts coincide with the felt reports: The 1,500-pound shot ﬁred at 3 a.m. on October 18 made the tremor which caused one person at Big Springs [sic] to think that an automobile bumped his house and another to think that someone was rattling the door; the 1,800-pound shot ﬁred at 6:15 a.m. coincides with the reports as to the strongest tremor felt.

Three 1,500-pound shots, in addition to several smaller shots, were ﬁred between 11:30 p.m. local time on 18 October and 5:55 a.m. local time on 19 October. Headline

Wichita Daily Times, 18 October 1929: “Series of Five Tremors at Big Spring”

Valentine—16 August 1931 This earthquake occurred near the West Texas town of Valentine and was felt over most of the state as well as in parts of New Mexico, Oklahoma, Kansas, and Mexico (see ﬁgure 2.4). The range of magnitudes it has been assigned is quite large—between 5.6 and 6.4. Dumas, Dorman, and Latham (1980) noted: Several previous authors have estimated the magnitude of the 1931 Texas earthquake. Gutenberg and Richter (1949) gave a value of 6.4. The same value was obtained by Sanford and Toppozada (1974) using a method based on the size of the felt area. Nuttli (1976) obtained a magnitude of 5.6 using the method of intensity gradient . . . Allowing for the difference between Rossi-Forel intensities and Modiﬁed Mercalli scales, one obtains agreement with Nuttli’s result by using the spacing of isoseismals normal to the trend of the valley . . . Parallel to the valley, the spacing of the isoseismals is greater, giving a magnitude of 5.9 by the same method.

More recently Doser (1987) used body waves to compute a moment magnitude Mw of 6.3. Notwithstanding the uncertainty about magnitude, this earthquake is undoubtedly the largest to have occurred in Texas in historic times. There is also uncertainty about the focal mechanism for this earthquake, even though three investigators have published mechanisms (see ﬁgure 9.10). A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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Figure 9.10. Summary of published focal mechanisms for Texas earthquakes. The text at right of lower-hemisphere focal plots indicates the year and location of the earthquake, the source reference for the mechanism, and the azimuth and plunge of the principal axes, labeled T (tension), B (null), and P (pressure) axes. Except for 1995 Alpine earthquake, the referenced sources either did not present numerical information for the azimuth and dip of the principal axes, or the numerical values presented were such that the T and P axes were not perpendicular. Thus we obtained the focal plots and numerical values here by fitting focal plots presented in the referenced sources.

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The mechanisms found include both a nearly pure dip-slip mechanism (Sanford and Toppozada 1974) and a nearly pure strike-slip mechanism (Dumas, Dorman, and Latham 1980). Finally, Doser (1987) obtained a third mechanism from a comparison of available waveforms and synthetics. We favor Doser’s mechanism, which is predominantly strike-slip. The highest intensities occurred in Valentine and surrounding towns. At Valentine, Neumann (1932) noted: Adobe buildings suffered most, although cement and brick walls were in some cases badly cracked. In one case a section of a low wall of reinforced concrete was broken and thrown down. All but frame houses were badly damaged and all brick chimneys toppled over or were badly damaged. The schoolhouse, consisting of one section built of cement blocks and another of brick, was reported to require practically complete rebuilding. Small cracks appeared in the schoolhouse yard. In other buildings adobe walls collapsed and in frame structures ceilings and partitions were damaged. Tombstones in the cemetery were rotated in both directions, in some instances as much as a quarter of a turn. The population was more or less panic stricken, but there were no fatalities and only a few were slightly injured by falling adobe. This is accounted for by the fact that nearly everyone was sleeping outdoors.

At Candelaria the “ground seemed to rise up in waves” (Neumann 1932). Chimneys were thrown to the ground at Alpine. The Amarillo Daily News reported that at Lobo “a few windows were shaken out,” buildings were cracked, and chimneys were knocked down or broken. Numerous landslides occurred in the epicentral region. According to the El Paso Times: In Valentine . . . word had been received that several smaller mountains in the range about 25 miles south of the city had entirely disappeared. Huge boulders were sent hurtling down mountainsides and into deep canyons. Great clouds of dust and smoke arose and hung over the country for several hours.

About 20 km southwest of Valentine a landslide buried a concrete tank to a depth of about 10 meters. There were also reports of landslides in the Chisos Mountains in the Big Bend area; near Pilares and Porvenir; in the Van Horn Mountains southwest of Lobo; in the Guadalupe Mountains near Carlsbad, New Mexico; and near Picacho, New Mexico (Sellards 1933b; Neumann 1932). Some residents of Tesnus, south of Fort Stockton, heard landslides in the nearby Glass Mountains.

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In several locations the earthquake affected well water quality. Sellards (1933b) found that “springs were muddied” in the area south of Valentine, and the “San Solomon Spring at Balmorhea [85 km northeast of Valentine] became muddy following the earthquake and was still disturbed . . . as late as August 19.” Neumann (1932) noted that Comanche Spring at Fort Stockton “spouted muddy water for an hour after the earthquake.” However, Kurtz and Goran (1986) stated that the Lone Pine Spring, which was a major water source for the Guadalupe Mountains, stopped ﬂowing after the earthquake. Listings of the earthquake’s effects (Sellards 1933b; Neumann 1932) indicate that at Van Horn (45 km to the north) chimneys fell, walls cracked, and a water pipe leaked. The earthquake split the seams of a steel tank at Fort Davis (66 km to the east), allowing water to escape, and a “roaring sound like a mighty wind was heard” (Sellards 1933b). At Marfa (68 km to the southeast), bricks fell from a chimney, cracks appeared in buildings, and there was a “rumbling sound like an approaching wind storm” (Sellards 1933b). The shock broke water pipes and damaged bridges at Ruidosa (50 km to the south). Farther south in Presidio (130 km away) there were cracks in several buildings. At Pecos (130 km northeast of the epicenter), the Pecos Enterprise and Gusher reported: Dishes rattled in closets. Doors slammed shut. Rocking chairs began moving grotesquely. Window weights hammered against the sides of houses, beds tipped from their moorings, chandeliers swayed like the pendulums of a clock, and houses creaked and groaned. Plaster also cracked in Pecos.

From Fort Stockton (160 km distant) came reports of cracked buildings and fallen plaster. At El Paso (220 km northwest of the epicenter) the shock broke a few dishes and “chairs moved, lights swayed, some persons left houses, and animals were disturbed” (Sellards 1933b). One resident reported that “a mirror suspended on the south wall swung in an arc which could be measured by the scratches on the wall. This arc measured 6 feet” (Neumann 1932). Across the river in Juarez, Mexico, adobe buildings suffered minor damage. At Carlsbad, New Mexico (190 km distant), the earthquake shook bricks from chimneys, knocked down pipes, and disturbed animals. The Houston Post-Dispatch reported that it also knocked sleepers from beds, rattled windows, broke dishes, and stopped clocks. The tremor was felt widely to the northeast of Valentine and in the Texas Panhandle. At Big Spring (350 km distant) there was “much confusion reported at the hotels, many of the guests in the upper ﬂoors having left their rooms” (Sel150

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lards 1933b). The Amarillo Daily News noted that one resident at Big Spring “was caught under the china cabinet in his dining room as it fell over.” Farther north in Lubbock (410 km away) the earthquake shook buildings, rattled dishes, and awakened sleepers. The Lubbock police received two calls from residents who thought burglars in their houses caused the shaking. At Tulia (500 km distant) the earthquake “rattled walls and jarred windows.” In Amarillo (560 km distant), “the shock was mild”; however, motion on the “upper ﬂoors of hotels . . . was quite appreciable” (Sellards 1933b). Many people there did not feel the tremor, but a few were awakened. At Pampa (590 km away) “windows and beds shook.” At Wichita Falls, Texas, the Wichita Daily Times reported that a few individuals were aware of the shocks, but the tremors were “so slight as to be passed unnoticed even by those who were awake at that early hour.” East of the epicenter at Brady (490 km distant) “about one-half [of the] people awakened; a few frightened; windows, dishes, furniture rattled.” “Beds rocked” at Laredo (590 km distant). Newspapers reported that in Austin (660 km away) windows rattled, beds shook and banged against walls, and lights and porch swings oscillated. “Window weights rattled” at Waco (710 km away); in Dallas (770 km away) the shock was “quite appreciable,” especially in tall buildings. Houses swayed in Sherman (820 km northeast of the epicenter), whereas at Bonham (850 km away) “few awakened; windows rattled; lights swayed; houses swayed gently” (Sellards 1933b). In San Antonio (600 km east of the epicenter), one resident heard a roaring sound, another reported “a sound as of rubber balls falling on the roof,” and a newspaper article said dishes were broken, windows rattled and chandeliers swayed, although no extensive damage was reported. The felt area may have extended as far east as Houston (890 km distant), where Neumann (1932) assigned an intensity I–III. The felt area extended to the northwest as far as Albuquerque, New Mexico (525 km distant). To the south in Jimenez, Mexico (410 km away), the earthquake was “mild, felt by few persons, no damage.” According to the Houston Post-Dispatch the earthquake was felt as far south as Oaxaca, Mexico, where houses collapsed and several people were injured. However, considering that Oaxaca is more than 1,750 km from the epicenter, it seems likely that a local earthquake and not the Valentine event caused the effects in Oaxaca, a seismically active region. Other sources that mention the 1931 Valentine earthquake include Byerly (1934a and 1934b), Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), Docekal (1970), Gordon (1983), Ni, Reilinger, and Brown (1981), Nuttli and Herrmann (1978), Pantex Facility (1975), A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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VALENTINE REGION — 16 AUGUST TO 26 AUGUST 1931 FORESHOCKS AND AFTERSHOCKS Origin time (largest shock): Location: Maximum intensity: Felt area: Magnitudes assigned:

19:36 UTC (18 August) 30.7 N 104.6 W V 20,000 km2 mN 4.2

Davis and others (1989) Neumann (1932) Davis and others (1989) Davis and others (1989); Nuttli (1979)

Reagor, Stover, and Algermissen (1982), Seismological Notes (1931), Stover and Coffman (1993), and von Hake (1977). Headlines

Amarillo Daily News, 17 August 1931: “Quake Rocks West Texas and New Mexico” Amarillo Daily News, 19 August 1931: “Terriﬁed Texans Sleep in Open after Quakes” El Paso Times, 17 August 1931: “Quake Rocks El Paso and Vicinity, $75,000 Damage Caused at Valentine” El Paso Times, 17 August 1931: “Valentine Again Hit by Quake” El Paso Times, 19 August 1931: “Say Mountains Disappeared during Severe Earthquake at Valentine” Houston Post-Dispatch, 17 August 1931: “Houses Crash as Quake Rocks West Texas Towns” Pecos Enterprise and Gusher, 21 August 1931: “Earthquake Rocks Pecos Homes Last Sunday” Pecos Enterprise and Gusher, 28 August 1931: “Quake Only ‘Slight’ Slip, Scientist Says” San Angelo Standard Times, 3 January 1992: “Even Earthquakes Can’t Shake Up West Texans” Wichita Daily Times, 17 August 1931: “Earth Quakes Rouse Texans, Damage Light”

Valentine Region—16 August to 26 August 1931 Foreshocks and Aftershocks The record shows that both foreshocks and aftershocks accompanied the Valentine earthquake of 16 August 1931. Seismographs at Denton, Texas; St. Louis, Missouri; and in Tucson, Arizona, recorded some of these events. However, most of what we know about them is based on felt reports, and many of these reports are confused or imprecise because of the large number of shocks.3 The essential facts are as follows: During the night prior to the main shock, several foreshocks frightened many people into sleeping outdoors, a fact that 152

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may account for the lack of fatalities or major injuries. For example, Dumas, Dorman, and Latham (1980) state that one family near the Davis Mountains (25 km east of the epicenter) slept outside “during most of the preceding night because they felt several shocks before the main shock.” Sellards (1933b) states: A great many people were awakened by the ﬁrst shock at 2 o’clock (some say 3 o’clock), and several felt two intervening shocks before the distinct one [main shock] at 4:40 [the times given are MST; the main shock occurred at 11:40 UTC]. Several people have said that the tremors at 2 and 4:40 were preceded by a roaring sound similar to an approaching wind storm, or a large rain or hail storm.

Several earthquakes occurred within eight hours following the main shock at 5:40 a.m. CST (11:40 UTC). Various contemporary accounts document aftershocks at 12:17 UTC, at 12:45 UTC, and at either 19:33 UTC or 20:33 UTC. There is some discrepancy in the time of the last event because of confusion about whether reported times refer to Central or Mountain Standard Time. The largest aftershock of the Valentine earthquake occurred on 18 August at 1:37 p.m. CST (19:37 UTC). The El Paso Times reported that it cracked walls and knocked bottles and cans from shelves at Valentine; it also caused the collapse of an adobe hut previously damaged by the main shock. Clocks stopped in El Paso, and felt reports came from Alpine, Lobo, Pecos, Fort Davis, and the Big Bend area in Texas and from Carlsbad, New Mexico. The Amarillo Daily News reported that “tremors of slight intensity” were felt in Dallas (770 km from the epicenter) although the time given was “shortly before noon” and not 1:37 p.m. CST. Perceptible aftershocks of the Valentine earthquake apparently continued for some time. Sellards (1933b) reported one on 26 August that was felt in Valentine, Alpine, Marfa, and Fort Davis, suggesting a felt area of 6,800 km2. He did not give the time of the event. Finally, Neumann (1932) lists an earthquake that occurred in Valentine on 3 November 1931 at 15:50 UTC: “Felt at Valentine. Aftershock of the August 16 earthquake. Recorded at Tucson.” Apparently solely on the basis of this report, the shock has been assigned maximum intensities of II (Nuttli 1979), III (Reagor, Stover, and Algermissen 1982), and V (Sanford and Toppozada 1974) and magnitudes of 3.0 and 3.2 (Davis, Pennington, and Carlson, 1989; Nuttli 1979). Other sources that mention these 1931 Valentine aftershocks include Byerly (1934a and 1934b), Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), Docekal (1970), Gordon (1983), Gutenberg and Richter (1949), Ni, Reilinger, and Brown (1981), Nuttli and Hermann A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

153

EL PASO — 2 OCTOBER 1931 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

Unknown 31.8 N 106.5 W II–III — mN 3.2

Docekal (1970) Seismological Notes (1931) Nuttli (1979)

WORTHAM-MEXIA — 9 APRIL 1932 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

10:17 UTC 31.7 N 96.4 W VI 6,400km2 mN 4.0; 4.0 mN 4.0

Reagor and others (1982) Reagor and others (1982) (This study) Davis and others (1989); Nuttli (1979) Nuttli (1979)

(1978), Pantex Facility (1975), Reagor, Stover, and Algermissen (1982), Seismological Notes (1931), and von Hake (1977). El Paso—2 October 1931 We have very little information about this shock. Seismological Notes (1931) says only that “an earthquake of a few seconds’ duration and intensity II–III was reported from El Paso on October 2d [sic],” while Neumann (1932) notes that “To-day [2 October 1931], a shock occurred at El Paso, Tex. Feeble.” Although Nuttli (1979) has estimated a magnitude of 3.2 from these reports, the shock may have been signiﬁcantly larger, especially as seismographs in Alaska, Hawaii, France, and Germany recorded it (Sellards 1933b ). It is possible this was an aftershock of the 16 August Valentine earthquake. Other sources that mention the 1931 El Paso earthquake include Comanche Peak Steam Electric System (1977), and Reagor, Stover, and Algermissen (1982). Wortham-Mexia—9 April 1932 In east-central Texas during the early morning hours of 9 April 1932, an earthquake occurred near the towns of Wortham and Mexia. It shook down bricks from several chimneys in Wortham and awakened sleepers in many neighboring towns. Sellards (1933a) thoroughly surveyed the felt area one month later and reported: The maximum distance at which the shock was at all perceptible to persons awake are as follows: Corsicana, 21 miles north of Wortham; Thornton, 19 miles south of Mexia; and Watts, 23 miles west of Mexia. The shock apparently was not perceptible at Fairﬁeld, 19 miles northeast of Wortham. 154

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Figure 9.11. Felt area map for the 9 April 1932 Wortham-Mexia earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded regions indicate major oil fields mapped by Galloway and others (1983) that were established prior to 1932. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989).

He noted that other towns feeling earthquake effects included Currie, Groesbeck, Richland, Teague, Prairie Hill, and Tehuacana. Other sources indicate that the earthquake was also felt in Hillsboro (75 km northwest of Mexia) and College Station (100 km south of Mexia) (Seismological Notes 1932; Neumann 1934). However, the College Station report is probably erroneous; while the Bryan Daily Eagle contained an Associated Press report ﬁled from Mexia, it does not mention that residents of either Bryan or nearby College Station felt the tremor. A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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TROUT SWITCH — 12 APRIL 1934 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

01:40 UTC 33.9 N 95.5 W V 13,000km2 mN 4.2

Docekal (1970) Neumann (1936) (This study) Davis and others (1989); Nuttli (1979)

The geologist’s report indicated that felt effects were greatest at Wortham, where the earthquake awakened most people. There bricks fell from at least four chimneys in the south and southwest parts of town, and a crack formed from the roof to the ground in the mortar of a one-story brick-veneer building. However, the report states that there were several cracks in this building before the earthquake and that the bricks that fell from at least one chimney separated upon falling, indicating that mortar had not held them ﬁrmly. At Mexia the effects were slightly less pronounced than at Wortham; only a few persons were awakened by the shock, which rattled dishes and stoves and caused buildings to creak. The geological report also noted a crack cutting across the concrete highway between Wortham and Mexia. The towns affected by this earthquake sit astride the Mexia Fault zone. These faults form structural traps for several large and highly productive oil ﬁelds; the total oil production in the Mexia ﬁeld to the end of 1931 was more than 90 million barrels. Both Sellards (1933a) and Yerkes and Castle (1976) have suggested that the Wortham-Mexia earthquake may have been induced by subsidence along a fault as a result of withdrawal of large volumes of gas, oil, and water from the producing oil ﬁelds in the area. Other sources that mention the 1932 WorthamMexia earthquake include Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), Docekal (1970), Sheets (1947), South Texas Nuclear Project (1978), Stover and Coffman (1993), and Varma (1975). Headline

Bryan Daily Eagle, 9 April 1932: “Earth Shock Felt in Many Texas Towns”

Trout Switch—12 April 1934 Residents of the towns of Powderly, Arthur City, Caviness, and Chicota, all in northern Lamar County in northeastern Texas, felt a fairly strong earthquake on the evening of 11 April 1934. Sellards (1935) canvassed the area shortly afterward and provided detailed felt reports. Although we have been unable to locate any city named Trout Switch on maps of today or from the time of the earthquake, this event has always been called the Trout Switch earthquake. Between Powderly and Arthur City, contemporary maps do show a railroad spur labeled Trout Spur that coincides with the center of the felt area; obviously this is Trout

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Figure 9.12. Felt area map for the 12 April 1934 Trout Switch and 31 May 1997 Commerce earthquakes. Roman numerals denote Modified Mercalli Intensities. Region labeled “I–III” represents felt area for 1934 earthquake only; region labeled “II–IV” is the felt area for 1997 earthquake. Dashed lines indicate county boundaries. Town labeled “AC” is Arthur City. Contemporary maps show no place named “Trout Switch”; presumably it is the same as Trout Spur. Shaded regions indicate major oil (dark shading) or gas (light shading) fields as mapped by Galloway and others (1983) and Kosters and others (1989) that were established prior to 1983; all of these fields were established after 1934. Isoseismals for the 1934 earthquake are revised using information reported by Davis, Pennington, and Carlson (1989).

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BAJA CALIFORNIA — 31 DECEMBER 1934 Origin time: Location: Felt area: Magnitudes assigned:

18:45:45 UTC 32.0 N 114.75 W 205,000km2 MS 7.0

Gutenberg and Richter (1949) Neumann (1936) Gutenberg and Richter (1949)

Switch. Here, a roaring preceded two tremors; at Arthur City and Powderly there was a rumbling and dishes rattled in houses; at Chicota, some people ran from their homes. In all four locations a majority of the population both felt and heard the earthquake, although no damage was reported. However, in Caviness the foundation of a house was disturbed and the owner had to use a house jack to relevel the structure to allow doors to close. Residents distinctly felt two shocks in Hugo, Oklahoma, and in Paris, Texas, where guests on the upper ﬂoors of a hotel were alarmed when the lights swayed. According to the Wichita Daily Times, a resident of Greenville, Texas, reported that “the shock caused a kerosene lamp to fall from a table in his home.” Seismographs at Florissant and St. Louis, Missouri, at Austin, Texas, and at Little Rock, Arkansas, recorded the earthquake. However, the P arrivals were either too emergent or only later phases were recognized, so an epicenter was not instrumentally determined. There is some discrepancy concerning the time of the shock. Neumann (1936) lists the time as 11:40 a.m. (17:40 UTC) on 11 April, and most subsequent catalogs use this time. However, both the original detailed geological report and the Wichita Daily Times conﬁrm that the shock occurred on the evening of 11 April at 7:40 p.m. (01:40 UTC on 12 April). Other sources that mention the 1934 Trout Switch earthquake include Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), Reagor, Stover, and Algermissen (1982), Sheets (1947), and Varma (1975). Headline

Wichita Daily Times, 12 April 1934: “Earth Tremor in North Texas and South Oklahoma”

Baja California—31 December 1934 Two large earthquakes occurred in Baja California on 30 and 31 December 1934; Neumann (1936) indicates that the second shock was felt with intensity III in El Paso, Texas. However, we regard this with some skepticism in view of El Paso’s distance from the epicenter (780 km) and as there were no felt reports from anywhere in New Mexico. The tremor may have been felt in some of El Paso’s higher buildings. The Houston Post and the Wichita Daily Times mentioned the California earthquake but made no reference to the shock being felt in El

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VALLIANT, OKLAHOMA — 14 MARCH 1936 Origin time: 17:20 UTC Location: 34.0 N 95.0 W Maximum intensity: V (in Oklahoma) Felt area: 2,300km2 Coffman and others (1982) Magnitudes assigned: mN 4.2

Docekal (1970) Docekal (1970)

Nuttli (1979)

Paso. Another source that mentions this earthquake is Coffman, von Hake, and Stover (1982). Headlines

Houston Post, 1 January 1935: “Earthquake Rocks Cities along Coast” Wichita Daily Times, 31 December 1934: “Sharp Quake Rocks California and Arizona” Wichita Daily Times, 1 January 1935: “No Serious Damage by Quake on Paciﬁc Coast”

East of Padre Island—3 July 1935 (Spurious earthquake report) A paper on diastrophism in the Gulf Coastal Plain (Sheets 1947) describes an event that some people thought resembled an earthquake: J. G. Burr, aquatic biologist with the Game, Fish, and Oyster Commission of Texas, reported that something resembling an earthquake occurred on the shore of the Gulf of Mexico on July 3, 1935, approximately 60 miles east of Padre Island. Many tons of ﬁsh were killed and hydrogen sulphide gas was produced. The United States Coast and Geodetic Survey was called on to investigate the possibility of an earthquake but found no actual evidence of any such occurrence. W. Armstrong Price reports on this matter that the ﬁsh were probably killed by a severe ﬂood of fresh water from the Nueces River. Also killed were many types of marine organisms among which were some jelly ﬁsh and associated echinoderms. These organisms produced a sulphurous acid and a greenish gas when stirred up by the Gulf spray.

There is no convincing evidence that this actually was an earthquake, and we include it here only for completeness. Valliant, Oklahoma—14 March 1936 An earthquake occurred in southeastern Oklahoma on 14 March 1936, at 11:20 a.m. (17:20 UTC). In Texas, Neumann (1938) reported that it produced intensity MMI III in Manchester, Texas, near the Texas-Oklahoma border, but it apparently was not felt in Bryarly, Medill, or Woodland. Other sources mentioning this earthquake include Coffman, von Hake, and Stover (1982), Comanche

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159

CLARENDON — 19 JUNE 1936 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

21:00 UTC (approx.) 35.2 N 100.7 W III Local mN 3.0

Davis and others (1989) Davis and others (1989) Davis and others (1989)

Peak Steam Electric System (1977), Seismological Notes (1936a), and Stover and others (1981). Headlines

Carthage (Texas) Panola Watchman, 19 March 1936: “Earthquake Felt in Oklahoma Friday” Wichita Daily Times, 15 March 1936: “Slight Earth Tremor Reported Idabel, Okla.”

Clarendon—19 June 1936 In discussing the 20 June 1936 Borger event, the Amarillo Daily News mentions another earthquake: He [editor of the Donley Count Leader] also reported another quake at the John Viaker Ranch, 25 miles northeast of Clarendon, at 3 o’clock in the afternoon. His check revealed the shock was felt 22 miles southwest and as far as the Viacker [sic] Ranch northeast.

The Lubbock Avalanche-Journal also mentions a 3 p.m. (local time) shock at Clarendon. This could be a foreshock of the Borger earthquake that was not noticed or reported elsewhere. Another possibility is that some local event, perhaps an explosion, was erroneously identiﬁed as an earthquake. Davis, Pennington, and Carlson (1989) categorized this event as a possible earthquake and assigned a location at 35.2 N, 100.7 W (the center of the area described above, that is, 23 km northeast of Clarendon). Borger—20 June 1936 On the evening of 19 June 1936 (local time), three earthquakes occurred, separated by intervals of four to ﬁve minutes.4 The third shock was by far the strongest; it was felt in parts of Texas, Oklahoma, Kansas, and Colorado and was recorded on seismographs as distant as Tucson, Arizona, and St. Louis, Missouri. Its effects were not as far-reaching as those of the 1925 earthquake, although people experienced moderate intensities (MMI IV–VI) over a considerable area. There has been some disagreement about the distribution and maximum intensity of felt reports for this earthquake. An article in the Amarillo Daily News indicates the maximum intensity was about MMI VI, as it noted that a man was

160

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BORGER — 20 JUNE 1936 Origin times (foreshocks) Location: Maximum intensity: Felt area: Magnitudes assigned:

03:13:37 UTC 03:18:27 UTC 35.7 N 101.4 W III–IV 21,000km2 mN 3.9; 3.0

Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

03:24:06 UTC 35.7 N 101.4 W VI 110,000km2 mN 5.0; 4.7

Docekal (1970) Davis and others (1989) (This study) Davis and others (1989)—both; Nuttli (1979)—both Docekal (1970) Docekal (1970) (This study) Davis and others (1989); Nuttli (1979)

knocked off his feet in Whittenberg near White Deer Creek in Hutchinson County. The man stated: The ground just came up and hit us in the face . . . The second [shock] really rocked the ground. Banks of the creek crumbled. We could hear a distant rumble. It sounded like a nitroglycerine explosion, or the roar of heavy thunder.

No doubt the intensities were as high as V in a large area of Texas. At Clarendon the earthquake “moved furniture and was more severe than the tremblor [sic] of 1925.” Dishes were knocked off shelves at Panhandle, and at Fritch the shock was “very severe.” At Sanford, near the future site of the dam for Lake Meredith (see table 5.1), Sellards (1939) reports that the shock was also quite strong: A shock and then a tremor felt by all persons of the community. The ﬁrst shock gave the effect of a house being run into, then the tremors were noticeable for perhaps 40 seconds. It seemed the tremors ran from north to south.

At White Deer it “felt as though the house would come to pieces if it [the earthquake] had lasted any longer.” Similar effects were noticed at Gruver: My family and I were in our old rock house which has stood in this Panhandle Country for ﬁfty years, and we were all frightened to death. The walls, ceiling and ﬂoor just quivered, and it seemed as though these old thick walls would never stand. It seemed as though the whole house was waving up and down. It was certainly a shock to the entire community.

The Amarillo Daily News said the earthquake caused damage at Pampa: The cornice of the Pampa city hall was cracked. A place on the south side where there was a half inch crack was widened to four and a half inches. A new crack, about 11 inches wide, was made on the north side.

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161

Figure 9.13. Felt area map for the 20 June 1936 Borger main shock. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded regions indicate major oil (dark shading) or gas (light shading) fields as mapped by Galloway and others (1983) and Kosters and others (1989) that were established prior to 1936. Map and isoseismals are revised from Davis, Pennington, and Carlson (1989), who incorporated information from Sellards (1939). For town locations see figure 9.8.

At Stinnett, people were frightened, and patrons of the 4-H Club Girls’ Personality Show ﬂed the building. They were later given their money back, and according to the newspaper article, “the damage done to the box ofﬁce [by refunding the money] . . . was more than that of all the remainder of the region put together.” Cities in southwest Kansas and the Oklahoma Panhandle also experienced 162

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intensities of IV to V. Although Sellards (1939) did not assign any intensities, his map gives an excellent indication of the limits of the perceptible shock. Two features concerning the felt area are apparent from his map. First, the isoseismals appear elongated in the north-south direction. Second, Kenton, Guymon, and Elmwood, Oklahoma, and Elkhart and Liberal, Kansas, have relatively high intensities, whereas many cities closer to the epicenter (Boise City, for example) have lower intensities. As with the 1925 Panhandle earthquake there was speculation that oil and gas ﬁelds may have caused the earthquake (see Canyon News article). Sellards (1939) discussed the possible relation of the earthquake to structural features: The controlling underground structural feature of the Panhandle region is the buried Amarillo mountain chain which trends approximately east-west. The place of maximum intensity of this earthquake was on the north ﬂank of this mountain structure and in part in the accompanying syncline of the Anadarko Basin to the north. The known lines of faulting in this region trend WNW-ESE. So far as can be judged from available records it does not appear that this earthquake represents slippage on any known line of faulting.

Other sources that mention this 1936 Borger earthquake include Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), Gordon (1983), Merriam (1956), Neumann (1938), Northrop and Sanford (1972), Nuttli and Herrmann (1978), Pantex Facility (1975), Seismological Notes (1936a and 1936b), Stover and Coffman (1993), and von Hake (1977). Headlines

Amarillo Daily News, 21 June 1936: “Plains Area, Shaken by Quake, Wakes Up Without a Hangover” Canyon News, 25 June 1936: “Earthquake Rocks Buildings in Panhandle Friday P.M.” Lubbock Avalanche-Journal, 20 June 1936: “Prophetic Young Woman at Texas Tech Forecasts Earth Shakes; Follow 45 Minutes Later in Area” Terry County Herald, 26 June 1936: “No Damage from Panhandle Tremors” Wichita Daily Times, 20 June 1936: “Slight Earth Tremors Felt Over Panhandle”

El Paso—8 August 1936 Several residents in eastern El Paso felt an earthquake at 7:40 p.m. on 7 August 1936 (01:40 UTC on August 8). According to the El Paso Times: A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

163

EL PASO — 8 AUGUST 1936 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

01:40 UTC 31.8 N 106.5 W III Local mN 3.0; 3.4

Docekal (1970) Sanford and Toppozada (1974) Davis and others (1989); Nuttli (1979)

EL PASO — 15 OCTOBER 1936 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

18:00 UTC (approx.) 31.8 N 106.5 W III local mN 3.0; 3.8

Docekal (1970) Sanford and Toppozada (1974) Davis and others (1989); Nuttli (1979)

Light ﬁxtures swayed, windows rattled and ﬂoors heaved as the distinct tremor was felt at 7:40 p.m., lasting from three to ﬁve seconds, according to reports of more than 100 persons. No damage was done.

The earthquake caused mirrors to rock and a water bottle at a ﬁre station to dance, and many residents heard a rumbling prior to the shock. One person reported, “We heard a mufﬂed roar, something like a blast, and then felt a decided jerk of the house. There was just one hard shake.” Other sources mentioning this earthquake include Comanche Peak Steam Electric System (1977), Neumann (1938), Reagor, Stover, and Algermissen (1982), and Seismological Notes (1936c). Headline

El Paso Times, 8 August 1936: “Earth Shock Hits El Paso at 7:40 p.m.”

El Paso—15 October 1936 Contemporary sources (Seismological Notes 1937; Neumann 1938) report that “an earth tremor rocked [El Paso] shortly before noon on October 15.” On the basis of this description subsequent investigators have assigned intensities of IV (Docekal 1970) and III (Sanford and Toppozada 1974). We have been unable to ﬁnd any reference to the earthquake in the El Paso Times. Other sources that mention this earthquake include Comanche Peak Steam Electric System (1977) and Reagor, Stover, and Algermissen (1982). El Paso—31 March 1937 Neumann (1940a) indicates that a “slight earthquake in El Paso” on 31 March 1937 was “felt by many.” Docekal (1970), referencing the El Paso Herald Post and unpublished archival records of the U.S. Coast and Geodetic Survey, states

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EL PASO — 31 MARCH 1937 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

23:45 UTC 31.7 N 106.5 W III local mN 3.0; 3.4

Sanford and Toppozada (1974) Docekal (1970) Docekal (1970) Davis and others (1989); Nuttli (1979)

EL PASO — 8 AUGUST 1937 (SPURIOUS EARTHQUAKE REPORT) Origin time:

01:40 UTC

(Docekal 1970)

that “two local shocks were felt in high buildings at El Paso, TX.” Estimates of the intensity at El Paso ranged from III to IV. Some discrepancy exists as to the date of the event. Although Neumann (1940a) and Sanford and Toppozada (1974) give the date as 31 March, Nuttli (1979) lists the date as 30 March, while Docekal (1970) records the date as “Mar 30, 31?” We have been unable to obtain copies of original sources to resolve the discrepancy. Other sources mentioning this 1937 El Paso earthquake include Comanche Peak Electric Steam (1977) and Reagor, Stover, and Algermissen (1982). El Paso—8 August 1937 (Spurious earthquake report) Docekal (1970) lists an earthquake on 7 August 1937, at 19:40 local time (01:40 UTC on 8 August); this is almost certainly an erroneous replication of the El Paso earthquake of 8 August 1936, at 01:40 UTC. His description reads: Many felt an east-west motion preceded by rumbling at El Paso, Texas. Water in a cooler was disturbed, hanging objects swayed but no alarm was evidenced.

Docekal’s sources are the unpublished archival records of the Coast and Geodetic Survey and the El Paso Times of 8 August 1937. The latter is probably a reference to the El Paso Times article of 8 August 1936 that mentioned rumbling sounds, a dancing water cooler, and swaying objects in connection with the 8 August 1936 El Paso earthquake. Other sources that mention this 1937 event include Comanche Peak Steam Electric System (1977) and Nuttli (1979). Alpine—1942, 1948 A paper on engineering geology adjacent to the Rio Grande (Henderson, Hughes, and Alfred 1959) notes that “small earthquakes rocked Alpine, TX, in 1942 and 1948.” The paper gives no other details, nor does it indicate the source of this in-

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165

DALHART — 12 MARCH 1948 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

04:29:00 UTC 36.0 N 102.5 W VI 240,000km2 mN 5.2; 4.7 mIV 5.25

Reagor and others (1982) Murphy and Ulrich (1951) (This study) Davis and others (1989); Nuttli (1979) Pantex Facility (1975)

formation. No other catalogs except Davis, Pennington, and Carlson (1989) list these events. Dalhart—12 March 1948 At approximately 10:30 p.m. CST (04:30 UTC) on 12 March 1948, a fairly large earthquake was felt in sections of Texas, Oklahoma, New Mexico, Colorado, and Kansas. Initially there was confusion about the quake’s location (Northrop and Sanford 1972): It was thought at ﬁrst that the epicenter was in northeastern New Mexico. As State Collaborator in Seismology for the Seismological Field Survey (U.S. Coast and Geodetic Survey) Northrop started a questionnaire-card survey. As reports began coming in, the net of coverage had to be expanded several successive times. The shock was reported felt at 82 localities and not felt at 79 other localities. The Seismological Field Survey had some difﬁculty locating the epicenter . . . Later, it was picked near Dalhart, Texas.

Murphy and Ulrich (1951) list twenty locations experiencing intensity MMI VI; however, as discussed by Davis, Pennington, and Carlson (1989), only three cities appear to warrant the rating. At Perico, Texas, the earthquake “awakened nearly all in the community. Cracked plaster and walls. Rumbling sound was heard by many before shock. Dogs barked. ‘House seemed to tilt east, then west, then a level quivering. Windows and dishes rattled.’” At Dalhart, Texas, the shock was: felt in all parts of town and rural areas. Many reported dull thud before shock. Railroad cars shook, popcorn machine in theater swayed. Ice was shaken from pipes and open faucets began to ﬂow. Hanging objects swung NE. One woman reported a bottle was shaken from a dresser.

At Regnier, Oklahoma: “Motion violent. Felt by and frightened all.” Elsewhere, although reports sometimes mention cracked plaster, the remainder of the descriptions and available newspaper reports suggest a lower intensity. For example, as Murphy and Ulrich (1951) found at Amarillo: Damage minor despite cracked plaster. Shook ﬂoors and rattled heavy steel doors of Potter County jail. Swooshing sound like large truck passing a car heard at time of 166

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Figure 9.14. Felt area map for the 12 March 1948 Dalhart earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded regions indicate major oil (dark shading) or gas (light shading) fields as mapped by Galloway and others (1983) and Kosters and others (1989) that were established prior to 1948. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989). For town locations see figure 9.8.

shock. Lamp shades moved for about 3 seconds. The Daily News newsroom was ﬂooded with calls, ﬁrst pattern of calls followed E.-W. line across Amarillo in the 1600 –1700 tier of blocks from Pierce Street west, then pattern of calls spread to other sections of town.

However, the Amarillo Daily News reported that: [One woman said] said “the dishes stacked in a rack in the kitchen rattled and a coffee pot fell from the cabinet. [A man] reported that a desk and a light shade in his A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

167

CHICO — 20 MARCH 1950 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

13:23 UTC 33.3 N 97.8 W IV — mN 3.3; 3.8

Varma (1975) Docekal (1970) Davis and others (1989), Nuttli (1979)

home was [sic] quivering slightly . . . [another man] said the movement was just like a passing train . . . Several guests [at the Herring Hotel] felt their beds quiver . . . [A resident] said lamp shades in his home started moving, and continued to do so for about three seconds . . . One woman reported that a hook on the door of her home sounded like the ticking of a clock.

We have been unable to locate any felt reports from other cities experiencing lower intensities. Other sources that mention the 1948 Dalhart earthquake include Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), Docekal (1970), Gordon (1983), Northrop and Sanford (1972), Nuttli and Herrmann (1978), Stover and Coffman (1993), and U.S. Coast and Geodetic Survey (1948). Headlines

Amarillo Daily News, 12 March 1948: “Temblor Jolts Plains” Canyon News, 18 March 1948: “Quake Hits Canyon Thursday Night” Daily Oklahoman, 12 March 1948: “Light Quake Jars Panhandle Cities” Houston Press, 12 March 1948: “Earthquake Shakes Panhandle; No Damage” Pampa News, 12 March 1948: “Earthquake Felt in Area” Wichita Daily Times, 12 March 1948: “Earth Shock Rocks Panhandle”

Chico—20 March 1950 We have found only one brief mention of this earthquake (Murphy and Ulrich 1952) that reportedly occurred in north-central Texas 75 km northwest of Fort Worth: Chico, Tex. One abrupt shock felt at the Centerville Powerhouse Camp. Flower pot moved and windows rattled.

This report forms the basis for all subsequent assignations of intensity and magnitude; the location of the Centerville Powerhouse Camp is unknown.5 Searches of the Dallas and Fort Worth newspapers reveal no mention of any unusual disturbances at Chico. Other sources that mention this 1950 Chico event include Comanche Peak Steam Electric System (1977), Docekal (1970), Reagor, Stover, and Algermissen (1982), and Varma (1975). 168

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AMARILLO — 20 JUNE 1951 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

18:37:10 UTC 35.0 N 102.0 W V 74,000km2 mN 4.2; 4.7 mf or mIV 4.75

Docekal (1970) Davis and others (1989) (This study) Davis and others (1989); Nuttli (1979) Pantex Facility (1975)

Amarillo—20 June 1951 An earthquake large enough to be felt throughout the western half of the Texas Panhandle occurred early in the afternoon of 20 June 1951; however, its epicenter is uncertain. Initial newspaper reports indicated it occurred near Hereford, Texas (34.8 N, 102.5 W). However, Docekal (1970) placed the epicenter at 35 N, 102 W, based on an interpretation of the isoseismal map. The International Seismological Summary instrumentally located it at 35.5 N, 103.0 W; however, this was based on only ﬁve P arrivals, with no reporting stations closer than 800 km. Incidentally, several sources incorrectly list the origin time as 19:37 UTC. Presumably this is a misinterpretation of times reported in newspapers, occurring because the epicentral area is near the time zone boundary between Central and Mountain Standard Time. The distribution of felt reports for this event is scattered and there are conﬂicting interpretations as to the maximum intensity. Several references variously assign MMI VI to Amarillo, Bovina, Hereford, and Plainview. However, MMI V seems more reasonable, as newspapers report little or no damage. For example, the Daily Oklahoman states that at Amarillo: First report of the tremor was from Amarillo highschool [sic] . . . Students said the furniture jigged and windows banged in the four-story brick building.

A report of damage to plaster in Hereford appears to have been an isolated incident; the Amarillo Daily News noted: An ofﬁce worker at a Hereford furniture store said a piece of plaster fell on her desk. She thought “some drunk in a Cadillac must have made a deposit” at the bank drivein window, next to the furniture store.

Reports of rattling windows came from Plainview, and the Austin American quoted the mayor, who said that “he and his daughter went outside ‘to see what happened’ after feeling the tremor.” The Amarillo Daily News described the effects at Borger, where: residents reported a noise “like snow falling off the roof.” The tremor rattled equipment in the control room of radio station KHUZ, and the station switchboard was swamped with calls from residents who had felt the earthquake. A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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Figure 9.15. Felt area map for the 20 June 1951 Amarillo earthquake; because of scatter in intensity reports, isoseismal lines could not be drawn. Dashed lines indicate county boundaries. Shaded regions indicate major oil (dark shading) or gas (light shading) fields as mapped by Galloway and others (1983) and Kosters and others (1989) that were established prior to 1951. Map is revised using information reported by Davis, Pennington, and Carlson (1989).

Nevertheless, the uncertainty about the location, origin time, and intensity of this event is peculiar. The scattered distribution of the higher intensities makes it difﬁcult to pinpoint the epicenter; many of the intensities assigned are not well constrained, and reports are unavailable from many cities that should have felt the shock. Other sources that mention the 1951 Amarillo earthquake include Coffman, von Hake, and Stover (1982), Gordon (1983), Murphy and Cloud (1953), Northrop and Sanford (1972), Nuttli and Herrmann (1978), Reagor, Stover, and Algermissen (1982), Seismological Notes (1951), and von Hake (1977). 170

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EL RENO, OKLAHOMA — 9 APRIL 1952 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

16:29:33.7 UTC 35.4 N 97.8 W VII (in Oklahoma) 640,000km2 mN 5.7; 5.5 mb 5.5; 5.9

Miller (1956) Murphy and Cloud (1954) (This study) Davis and others (1989); Nuttli (1979) PAS—Pasadena CA station; Pantex Facility (1975)

Headlines

Amarillo Daily News, 21 June 1951: “Earthquake Rattles Buildings All over Panhandle” Amarillo Daily News, 21 June 1951: “Tremor Writes Wavy Record” Amarillo Globe, 21 June 1951: “Hey, That Was an Earthquake” Austin American, 21 June 1951: “Earth Tremor Jars Panhandle Area” Canyon City News, 28 June 1951: “Tremor Rattles Dishes, People in Canyon and Area Wednesday” Crosbyton Review, 21 June 1951: “County Gets All Kind of Weather but Misses Hails and Earthquake” Daily Oklahoman, 21 June 1951: “Amarillo Hit by Dish Rattler” Lubbock Evening Journal, 20 June 1951: “Homes and Buildings Shaken as Earth Tremor Hits Panhandle-Plains Area” Lubbock Evening Journal, 21 June 1951: “Slippage of Rock Layers Blamed for Tremor” Lubbock Morning Avalanche, 21 June 1951: “South Plains, Panhandle Towns Shaken by Earth Tremor”

El Reno, Oklahoma—9 April 1952 One of the larger known earthquakes in the central United States occurred in Oklahoma in the late morning of 9 April 1952. The Daily Oklahoman reported that many people initially thought that an atomic bomb had been dropped on Oklahoma. Buildings were damaged in seven Oklahoma cities as intensities reached MMI VII in much of central Oklahoma. However, only two injuries were reported: one man slipped in a bathtub in Oklahoma City and had to get several stitches, and a woman in Tulsa was bruised by falling plaster. The Austin American reported that residents of several central Texas cities felt the earthquake. In Denison some residents ran from their homes. At Vernon it felt “as if someone had shaken the whole building gently.” Elsewhere felt reports came from people on the upper ﬂoors of buildings, including the fourteenth ﬂoor of a bank in Wichita Falls, the sixth ﬂoor of the Hendrick Memorial Hospital in Abilene, and the fourth ﬂoor of the Capitol building in Austin. Although A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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Figure 9.16. Felt area map for the 9 April 1952 El Reno, Oklahoma, earthquake. The epicenter of the shock was near the town of El Reno, Oklahoma, within the intensity VII area shown above. Roman numerals denote Modified Mercalli Intensities. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989), who incorporated information from Docekal (1970).

the Austin American reported that Amarillo residents felt the shock, we have found no details for any cities in the Texas Panhandle. Intensity maps prepared by Murphy and Cloud (1954) and Docekal (1970) indicate that the higher-intensity isoseismals are elongated in a north-south direction, approximately following the trend of the Nemaha Ridge in Oklahoma and Kansas. Because of this, several investigators suggested a relationship between this structure and the earthquake, or that it might also be related to the Anadarko Basin (Heinrich 1952; Lee 1954; Murphy and Cloud 1954; Miller 1956). Initially, the U.S. Coast and Geodetic Survey used an apparent depth phase to estimate a focal depth of 125 km for this event. However, subsequent investigations by Heinrich (1952) and Miller (1956) concluded that a shallow focus of 5 to 10 km was more reasonable. Other sources that mention the 1952 El Reno earth-

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ORANGE — 17 OCTOBER 1952 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

15:48 UTC 30.1 N 93.8 W IV — mN 3.3; 3.8

Reagor and others (1982) Murphy and Cloud (1954) Davis and others (1989); Nuttli (1979)

quake include Coffman, von Hake, and Stover (1982), Merriam (1956), Nuttli and Hermann (1978), Seismological Notes (1952), Stover and others (1981), Stover and Coffman (1993), as well as the Oklahoma Daily and the Tulsa Daily World of 10 April 1952. Orange—17 October 1952 One of the more bizarre occurrences in the history of Texas seismicity took place in Orange, Texas, during the morning hours of 17 October 1952. Several residents of Orange and nearby Lake Charles, Louisiana, reported seeing a “mysterious glowing object” that circled overhead for several hours in the predawn skies; this object then purportedly crashed at 9 : 30 a.m., causing a shock and an accompanying boom. According to articles in the Orange Leader and the Austin Statesman Captain E. G. Sparks of the Orange Police Department ﬁrst sighted the object at about 3:30 a.m. and noted that it was “very high in the sky and glowing bright red with a luminous trail.” When desk Sergeant T. O. Tinsley came on duty at 6:30 a.m. he also reported seeing the object and watched while it “went in all directions, sometimes at unbelievable speeds, and then appeared stationary at times.” Tinsley stated that the object turned a bright blue as the dawn approached and ﬁnally disappeared from his view behind trees that obstructed his vision. It was Sergeant Tinsley who phoned the Orange Leader at about noon and suggested that there might be some connection between the mysterious object and the tremor and boom felt at 9:48 a.m. It is probable that what Captain Sparks saw at 3:30 a.m. was a meteor or meteorite. According to the Austin Statesman: Reports of a similar object over Tennessee, Arkansas, Louisiana, and Mississippi came from airplane pilots. These pilots reported to the Airways Trafﬁc Control Headquarters in New Orleans of seeing at 4:40 a.m. a “meteorite which seemed to explode at a very high altitude.” The ﬂash across the early dawn skies caused an erroneous report of an airplane crash near McNeill, Mississippi.

What Sergeant Tinsley saw from 6:30 a.m. until sunrise is unknown; possibly it was some atmospheric phenomenon, an early morning star or planet, or even an airplane reﬂecting sunlight. Whatever the explanation, the mysterious

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VALENTINE — 27 JANUARY 1955 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

00:37 UTC 30.6 N 104.5 W IV — mN 3.3; 3.8

Docekal (1970) Docekal (1970) Davis and others (1989); Nuttli (1979)

object and the tremor that occurred several hours later at 9:48 a.m. (15:48 UTC) were probably unrelated. When separated from the earlier events, the tremor exhibits the characteristics of a small earthquake, or possibly a sonic boom. According to an article in the Galveston Daily News: Kent L. Franks, maintenance supervisor of the local telephone company, said that he was sitting on an ofﬁce desk and felt the building sway and heard the windows rattle. He also heard a dull boom. A lineman atop a pole also said he felt the pole shake at the same time.

Many residents of Orange felt the shock and heard rumbling. This event is only 50 km from the epicenter of an instrumentally well-recorded magnitude 3.8 earthquake (see Stevenson and Agnew 1988) that occurred near Lake Charles, Louisiana, on 29 October 1983. Other sources that mention the 1952 Orange event include Comanche Peak Steam Electric System (1977), Docekal (1970), and Varma (1975). Headlines

Austin Statesman, 18 October 1952: “Flying, Glowing Object Gives Coastal Residents ‘Quivers’” Galveston Daily News, 18 October 1952: “Quake Probe at Orange” Orange Leader, 17 October 1952: “Mysterious Object in Sky and Tremor Aground Puzzling Orange Residents”

Valentine—27 January 1955 The town of Valentine experienced a small shock on 26 January 1955 at 6:37 p.m. (00:37 UTC on 27 January). According to Murphy and Cloud (1957), it was “felt by many. Houses shook.” The Corpus Christi Caller reported that the earthquake was slight and produced no damage. Other sources that mention this 1955 Valentine earthquake include Comanche Peak Steam Electric System (1977), Docekal (1970), Reagor, Stover, and Algermissen (1982), and Sanford and Toppozada (1974). Headline

Corpus Christi Caller, 28 January 1955: “Texas Town Shaken by Slight Earthquake”

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GALVESTON — 7 JANUARY 1956 (PROBABLE SONIC BOOMS) Origin time: Location:

23:30 UTC 29.3 N 94.8 W

Galveston—7 January 1956 (Probable sonic booms) In the late afternoon of 7 January many residents of Galveston Island felt a series of tremors that shook houses and rattled windows and dishes. Persons wanting to know the cause of the disturbances ﬂooded the ofﬁces of the daily newspaper and local radio station with telephone calls and stated that loud rumblings accompanied the shocks. The Galveston Daily News related the observations of a Dr. H. W. Paley of Galveston, who: said he experienced three distinct ground shocks between 5:30 and 6:30 p.m. Each lasted no more than a second and he heard no rumbling afterwards. In between the shocks there seemed to be nothing abnormal, the doctor reported. In a split second before one of the shocks Dr. Paley said he felt as though there might be air concussion prior to the ground shock. Mrs. Paley said she had felt similar shocks at various times during the past several months but none were as severe as the ones Saturday.

The article also noted that news of the disturbance reached other parts of Texas and that the Galveston Daily News received calls from Houston and Dallas asking for an estimate of damage done. According to the article, this incident is probably a series of sonic booms rather than earthquakes. The short duration of the events as described by Dr. Paley, the air concussion prior to the ground shock, and the evidence of similar shocks occurring regularly prior to this event are all consistent with sonic booms or explosions. Nevertheless, subsequent investigators of this event have assigned an intensity of MMI IV (Brazee and Cloud 1958) and a magnitude of 3.8 (Nuttli 1979). Other sources that mention these 1956 Galveston events include Comanche Peak Steam Electric System (1977), Docekal (1970), Reagor, Stover, and Algermissen (1982), South Texas Nuclear Project (1978), Varma (1975) and Davis, Pennington, and Carlson (1989). Headline

Galveston Daily News, 8 January 1956: “Reported Explosions Here Unexplained”

Catoosa, Oklahoma—30 October 1956 An earthquake at 4:36 a.m. (10:36 UTC) awakened residents of several northeastern Oklahoma cities, including Catoosa, where an oil well was supposedly shut down by a slippage of the formation, and Tulsa, where there were reports of cracked plaster, chipped cups and saucers, and one cracked foundation. Brazee and Cloud (1958) assigned Electra, Texas, an intensity MMI IV but did not report details of the quake’s effects at Electra. Electra is about 370 km southwest of the A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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CATOOSA, OKLAHOMA — 30 OCTOBER 1956 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

10:36:21 UTC 36.2 N 95.8 W VII (in Oklahoma) 24,000km2 mN 4.7 ML 4.0

Stover and others (1981) Brazee and Cloud (1958) Docekal (1970) Nuttli (1979) SLM—St. Louis MO station

GLADEWATER — 19 MARCH 1957 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

16:37:39 UTC 32.6 N 94.7 W V 45,000km2 mN 4.7; 4.7

Docekal (1970) Brazee and Cloud (1959) (This study) Davis and others (1989); Nuttli (1979)

Aftershock origin times:

17:41:17 UTC 22:36 UTC 22:45 UTC 3,000km2 (all) III (all) mN 3.0 (all)

Davis and others (1989) Nuttli (1979) Davis and others (1989); Nuttli (1979)

Felt areas: Maximum intensity: Magnitudes:

epicenter and nearly 250 km from the southwestern edge of the felt area as mapped by Docekal (1970), thus probably the intensity IV rating was spurious. Other sources that mention this 1956 Oklahoma earthquake include Coffman, von Hake, and Stover (1982), Gordon (1983), Nuttli and Herrmann (1978), Pantex Facility (1975), and Varma (1975). Headlines

Tulsa Daily World, 31 October 1956: “Quake Rocks Tulsa Region” Wichita Falls Times, 30 October 1956: “Tremor Felt in Tulsa Area”

Gladewater—19 March 1957 On 19 March at least four earthquakes occurring near the towns of Gladewater, Longview, and Marshall rattled homes in northeastern Texas, northwestern Louisiana, and southwestern Arkansas. The area experiencing MMI V was about 6,000 km2. At Diana the earthquakes were felt by all, and many were alarmed; trees swayed, buildings creaked, loose objects rattled, and some objects moved. At Gladewater a clock fell from a wall, buildings creaked, and venetian blinds rattled. At Marshall a telephone receiver fell off its cradle and plants fell from ledges; houses shook, windows and dishes rattled, a closed door popped open, and numerous vases and glasses overturned.

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Figure 9.17. Felt area map for the 19 March 1957 Gladewater earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded regions indicate major oil (dark shading) or gas (light shading) fields as mapped by Galloway and others (1983) and Kosters and others (1989) that were established prior to 1957. The solid black region between the towns of Jefferson and Diana is Lake o’ the Pines. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989), who incorporated information from Docekal (1970).

There is a discrepancy concerning the location of the two afternoon aftershocks. According to an article in the Dallas Morning News the earthquake at 4:36 p.m. was felt in the Atlanta-Linden-Daingerﬁeld area, some 70 km northeast of its presumed epicenter, whereas the 4:45 p.m. shock was reported felt in Marshall. We assume that all four earthquakes occurred and were felt in the same region although we cannot verify this. The seismograph at Southern Methodist University in Dallas recorded the ﬁrst two shocks, but no instrumental location was possible.

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TEXAS PANHANDLE — 10 FEBRUARY 1959 (PROBABLE SONIC BOOMS) Origin time: Location:

20:05 UTC Texas Panhandle and eastern New Mexico

In the isoseismal map initially published for these events (Brazee and Cloud 1959), the area of maximum reported intensity is inconsistent with the published felt reports; Docekal’s (1970) revised map better represents the felt reports. The two maps agree concerning the areal extent of maximum intensity. However, in the revised map it is slightly to the north and includes the towns of Diana, Harleton, and Jefferson. The epicentral location coincides closely with the East Texas oil ﬁeld, one of the largest oil ﬁelds in the contiguous United States. Several investigators have suggested that subsidence due to ﬂuid extraction may have caused the earthquakes (Docekal 1970; Yerkes and Castle 1976). Incidentally, these earthquakes occurred during the construction of the Ferrells Bridge dam that impounds Lake o’ the Pines. However, it is unlikely that this project induced the swarm, as deliberate impoundment began in August, ﬁve months after the swarm occurred, and because the center of the MMI V area is situated about 40 km distant from the Ferrells Bridge dam (see table 5.1). The Houston Post reported a minor earthquake scare in the Houston area on 20 March 1957, the day following the Gladewater earthquakes. Several residents reported feeling earth tremors around 9 p.m. However, the weather was stormy, and strong winds or thunder probably caused the shaking. Local seismographs recorded no seismic activity at this time. Other sources that mention the 1957 Gladewater earthquakes include Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), Reagor, Stover, and Algermissen (1982), and Varma (1975). Headlines

Dallas Morning News, 20 March 1957: “Tremors Shake East Texas” Houston Post, 20 March 1957: “Earth Tremors Felt in Wide Area of East Texas” Houston Post, 21 March 1957: “Earthquake Scare Leads Squall Line Over Houston”

Texas Panhandle—10 February 1959 (Probable sonic booms) This event, which was almost certainly a series of sonic booms, is included here because several catalogs have listed it as an earthquake. The original description (Seismological Notes 1959) of the event as an earthquake, in its entirety, reads: Texas, February 10, 1959. A large section of the Texas Panhandle was shaken by an earth tremor about 2:06 p.m. At Pampa, north of Amarillo, a wall was reported to have cracked. The earthquake was also felt at McLean, Friona, and Canyon.

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Docekal (1970) also lists this event, citing the above as his only source. His comments are basically the same as the above text, with the exception of the word “well” replacing “wall.” On the basis of this information, he assigned an epicentral location at the town of Pampa (35.5 N, 100.9 W), a maximum intensity of V, and a felt area of 120,000 km2. Subsequent mentions of this event (Nuttli 1979; Reagor, Stover, and Algermissen 1982) use Docekal (1970) as their reference. Comanche Peak Steam Electric System (1977) lists it as occurring on 2 February 1959; this date is almost certainly a typographical error. Newspaper reports help to clear the confusion. The Amarillo Daily News reported two distinct blasts shortly after 2 p.m.; however, the seismograph in Lubbock recorded only a slight motion, while those in Dallas, Denver, and Tucson registered nothing at all. One Amarillo resident said the tremor was unlike an earthquake she had experienced in Amarillo several years before. Southeast of Claude, Texas, no ground movement was reported but “it seemed as though the sound came from the air.” Cities where residents heard or felt the blast included Higgins, Perryton, McLean, Amarillo, Claude, and Friona in Texas, as well as Clovis, Portales, and Roswell in New Mexico (see ﬁgure 5.7). The Chicago Daily Tribune added Pampa to the list, where the “wall of a business building was reported to have cracked.” In the next few days other parts of the country experienced similar blasts. The Amarillo Daily News reported that Flagstaff, Arizona, felt three tremors ﬁfteen hours after the event. However, the newspaper described the tremors as “unexplained” and suggested they might have been caused by “a meteor or some other space phenomena.” The Austin American noted another blast heard in Greenville, Texas (northeast of Dallas), on the night of 12 February, and the Amarillo Daily News reported three similar events in the Paciﬁc Northwest that same night. According to the Amarillo Daily News, explanations proposed for the events included bolides (exploding meteors), sonic booms, and earthquakes. One woman suggested that the blasts might be Soviet test missiles aimed near various U.S. cities. Although several Air Force bases initially denied responsibility for the blasts, Convair at Fort Worth, Texas, later admitted to testing a B-58 supersonic aircraft in the Panhandle area on 10 February. Convair did not reveal the ﬂight path, but in view of the descriptions and the locations of the felt reports it seems clear that this event was a series of sonic booms.

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LAWTON, OKLAHOMA — 17 JUNE 1959 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

10:27:07 UTC 34.5 N 98.5 W VI (in Oklahoma) 37,000km2 mN 4.7

International Seismological Centre Eppley and Cloud (1961) Docekal (1970) Nuttli (1979)

Headlines

Amarillo Daily News, 11 February 1959: “Whatsit Rocks Golden Spread” Amarillo Daily News, 12 February 1959: “Northwest Feels Jolts” Amarillo Daily News, 12 February 1959: “Three Tremors Rock Arizona” Amarillo Daily News, 14 February 1959: “Evidence Shows Sonic Boom Cause of Mystery Jolt Here” Amarillo Daily News, 14 February 1959: “It Could Have Been Khrushchev Testing” Austin American, 11 February 1959: “Quake? Panhandle is Rocked by Shock” Austin American, 13 February 1959: “Greenville Mystiﬁed by Blast” Chicago Daily Tribune, 11 February 1959: “Texas Shaken but They Deny It’s a Tremor”

Lawton, Oklahoma—17 June 1959 On this date at 4:27 a.m. local time a small earthquake occurred in southern Oklahoma. The cities of Duncan, Lawton, and Cache experienced intensities of MMI V to VI; all three towns reported cracks in concrete and plaster, and loud noises accompanied the shock at many locations. A few cities in Texas also felt the shock. In Wichita Falls most people did not notice it “but a few said they were awakened from their sleep. . . . [One woman] said the bricks of her home were shaken.” The Fort Worth Star-Telegram reported that one Dallas resident “ﬁrst thought the shaking was due to his foundation settling” and stated that residents of Gainesville and Nocona also felt the tremor. Other sources that mention this earthquake include Eppley and Cloud (1961), Gordon (1983), Pantex Facility (1975), and Stover and others (1981). Headlines

Fort Worth Star-Telegram, 17 June 1959: “Slight Quake Shakes Dallas for 5 Seconds” Frederick Leader, 17 June 1959: “Tremor Shakes Area” Pauls Valley Daily Democrat, 17 June 1959: “Local Citizens Report ‘Shakes’ from Tremor” Wichita Daily Times, 17 June 1959: “Wichitans ‘Shaken’ by Slight Tremor”

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ALASKA — 28 MARCH 1964 Origin time: Location: Maximum intensity: Magnitudes assigned:

03:36:14 UTC 61.05 N 147.48 W I (in Texas) Mw 9.2

International Seismological Centre Davis and others (1989) Stover and Coffman (1993)

Alaska—28 March 1964 We describe the Great Alaskan Earthquake of 1964 because it produced unusual surface-wave effects in Texas and adjoining states. There were ﬂuctuations of up to 22 cm reported in water well levels in the Texas Panhandle (Miller and Reddell 1964). More than twenty wells pumped large amounts of sand after the earthquake, and many wells decreased production for several hours. One well casing was sheared, forcing abandonment of the well. The Panhandle was not the only area affected by the surface waves. Montgomery (1964) reported well ﬂuctuations of several feet in Bexar County, Texas. There were seiches, or oscillations in water bodies responding to surface wave motion, recorded throughout the United States, especially near the Gulf Coast. Waves up to 1.8 m high overturned small boats and caused minor damage in several channels along the Texas and Louisiana coasts, and newspapers widely reported water sloshing over the sides of swimming pools. The ground motion may have been especially large because of the thick column of sediments near the Gulf Coast; one measurement of the ﬁrst mode Rayleigh waves (period 16 seconds) suggests the peak-to-peak amplitude may have been as high as 15 cm near Houston (Donn 1964). However, probably few people felt the motion because of the long periods of the waves. The only known felt report from Texas and adjoining regions was from a bridge tender just east of New Orleans, Louisiana, who felt sharp, well-deﬁned shakes on the bridge (Spaeth and Berkman 1969). Other sources that mention the effects of the 1964 Alaska earthquake in Texas include Cloud and Scott (1969), McGarr (1965), and McGarr and Vorhis (1968a and 1968b).6 Headlines

Abilene Reporter News, 29 March 1964: “Little Twitch Shakes Coast” Amarillo Daily News, 28 March 1964: “Earth Moves in Louisiana” Amarillo Daily News, 29 March 1964: “Shock Waves Belt Louisiana, Texas”

Hemphill-Pineland—24 April to 19 August 1964 Between 24 April and 19 August 1964 several earthquakes with magnitude of 4.0 and greater shook the Hemphill-Pineland-Milam-Bronson area of Sabine County in eastern Texas. Altogether, local residents felt dozens of events, causing a gen-

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HEMPHILL-PINELAND — 24 APRIL TO 19 AUGUST 1964 Origin time: (Largest event): Location: Maximum intensity: Felt area: Magnitudes assigned:

21:18 UTC (April 28) 31.3 N 93.8 W VI 2,700km2 mb 4.4; 3.8; 4.4

mN 4.0

Davis and others (1989) von Hake and Cloud (1966) (This study) von Hake and Cloud (1966); International Seismological Centre; U.S. Coast and Geodetic Survey Davis and others (1989)

eral feeling of apprehension and uneasiness; however, the only damage reported was from Hemphill on 28 April, when wallpaper and plaster cracked. Although recorded on numerous seismographs, the epicentral locations and focal depths were poorly constrained, and locations were assigned largely on the basis of felt reports. The swarm began on the evening of 23 April, when an earthquake with intensity MMI V rattled residents of Hemphill, Pineland, and Milam. Several other tremors were felt that night, and for the next two weeks residents felt at least one each day. From 23 April to 7 May, seismographs recorded more than forty earthquakes ranging in magnitude from 1.9 to 4.4. The Orange Leader reported that on 27 April, a small ﬁssure opened up in the backyard of a resident of Plainview, and water rose in a column 5 inches high. The largest of the earthquakes occurred at 3:18 p.m. CDT on 28 April; during this earthquake, knickknacks fell from shelves, furniture moved, buildings creaked, and loose objects rattled. After 7 May the earthquake activity decreased, although there was one event on 2 June, four on 3 June, two on 16 August, and one on 19 August. A seismograph deployed in July 1964 at an abandoned pumping station in Hemphill recorded more than seventy earthquakes; however, it found no activity after August 19 (Henley 1966). Davis, Pennington, and Carlson (1989) include a list of all located events having a magnitude exceeding 2.5. The origin of Hemphill earthquakes is uncertain. Although the epicentral area lies directly between two large reservoirs (Sam Rayburn to the west, Toledo Bend to the east), it is unlikely that inﬁlling caused the earthquakes (see table 5.1). At the time of the earthquakes construction had not yet begun on Toledo Bend Dam; Sam Rayburn Dam was nearly ﬁnished, but deliberate impoundment of water behind the dam did not begin until 1965. Several faults exist in the epicentral area, but none is obviously responsible for the activity. Other sources that mention the 1964 Hemphill-Pineland sequence include Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), Docekal (1970), Gordon (1983), Nuttli (1979), Nuttli and Herrmann (1978),

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Figure 9.18. Felt area map for the 28 April 1964 Hemphill earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded region indicates a major gas field as mapped by Kosters and others (1989) that was established prior to 1964. The solid black regions indicate the present-day extent of the Toledo Bend and Sam Rayburn Reservoirs. The Sam Rayburn Reservoir dam was under construction at the time of this quake; construction on the Toledo Bend Reservoir dam had not yet begun. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989).

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Kermit — 30 August 1965 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

05:17:30 UTC 31.9 N 103.0 W — — mb 3.5 ML 2.6; 3.3 Mcorr 2.9 mN 3.5

Sanford and others (1978)

U.S. Geological Survey Sanford and others (1978); Sanford and Toppozada (1974) Rogers and Malkiel (1979) Nuttli (1979)

Racine and Klouda (1980), South Texas Nuclear Project (1978), United Electrodynamics (1965), and von Hake (1977). Headlines

Corpus Christi Caller, 25 April 1964: “East Texas Jolted by Tremors” Houston Post, 25 April 1964: “World, E Texas Quakes Recorded at Rice” Orange Leader, 28 April 1964: “East Texas Tremors ‘Astonish’ Rice Scientist”

Kermit—30 August 1965 The earliest reported felt earthquake near Kermit, Texas, occurred at 05:17 UTC on 30 August 1965. Several catalogs list intensity MMI IV for this shock and reference Nuttli and Herrmann (1978), who do not specify the source of their information. After a better-documented felt earthquake at Kermit occurred on 14 August 1966, the Midland Reporter-Telegram noted: [the news director of a local radio station] said that earthquakes are not uncommon here [in Kermit] but this was the most severe one he had experienced.

Several catalogs list the epicenter as 32.1 N, 102.3 W, near Midland, Texas. However, because there were several instrumentally determined epicenters near Kermit during this time, we believe that the location of Sanford and others (1978) is more reasonable. Other sources mentioning this 1965 Kermit earthquake include Comanche Peak Steam Electric System (1977), Gordon (1983), the International Seismological Centre, Racine and Klouda (1980), Reagor, Stover, and Algermissen (1982), and Sanford and Toppozada (1974). Headline

Midland Reporter-Telegram, 15 August 1966: “Light Quake Jolts Kermit, Wink Areas”

Beaumont–Port Arthur—15 January to 24 March 1966 (Probable sonic booms) On ﬁve separate days in January, February, and March 1966, numerous citizens of southeastern Texas and southwestern Louisiana reported feeling a series of tremors that rattled windows and shook objects on shelves. According to von 184

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Figure 9.19. Cities in the Beaumont–Port Arthur area where people reported sonic booms, 15 January–24 March 1966. Map is revised using information reported by Davis, Pennington, and Carlson (1989).

Hake and Cloud (1968), the ﬁrst shock occurred at about 2 p.m. CST on Saturday, 15 January. The Beaumont Enterprise reported that residents felt a mild tremor and a “feeling of increased atmospheric pressure.” A second, similar shock occurred at 1:30 p.m. CST on 1 February. The largest and most widely felt tremor occurred at approximately 5:15 p.m. CST on 2 February. This produced the highest intensities (MMI V) at Beaumont and Port Arthur, and felt reports came from Texas City, Galveston, Anahuac, Liberty, Woodville, and Jasper in Texas and Leesville, Fort Polk, and Lake Charles in Louisiana. The Houston Post reported that the home of a woman in Texas City shook so badly that a light ﬁxture fell from the ceiling. The Beaumont Enterprise stated that 24 km north of Beaumont “dishes fell from shaking shelves A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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and pine trees swayed two or three feet” during the tremor. Several people in Beaumont said they felt a distinct buildup in pressure just before the tremor but that they heard little or no sound. Plate-glass windows at a shopping center rattled, and two walls in Beaumont were reported to have cracked. A Beaumont woman described a pulsation to the tremors and felt at least four separate tremors. The tremors continued to occur; the Houston Post reported that a shock at 4:20 p.m. CST on 3 February cracked a ceiling at a home in Beaumont. The last tremor occurred at about 5:45 p.m. CST on 24 March. Residents in Beaumont, Bridge City, Port Arthur, and Port Neches reported up to three separate shocks. At an apartment in Beaumont, one shock rattled venetian blinds and shook wall heaters. Another resident felt one tremor at 5:48 p.m. CST that lasted about ﬁfteen seconds, followed by another of shorter duration one minute later. A person in Bridge City felt three tremors “of brief duration” over a two-minute period. Docekal (1970) lists the March 24 event as occurring in Saline, Texas, citing an article in the Port Arthur News of 25 March 1966. However, since Saline, Texas, is situated several hundred kilometers to the west near Junction, Docekal was probably referring to the town of Sabine, 20 km south of Port Arthur. What caused these tremors? The Beaumont Enterprise reported that scientists at Southern Methodist University identiﬁed the February tremors as mild earthquakes, but the article provided no details about why they reached this conclusion. Seismographs at Rice University and at Beaumont failed to record anything unusual. However, there are strong indications that these events were actually a series of sonic booms. All ﬁve events occurred during daylight hours, between 1:30 and 5:45 p.m. CST, and several reports indicated a noticeable pressure change before the tremors. The strongest evidence comes from spokesmen for the General Dynamics Corporation in Fort Worth, which manufactured the F-111 ﬁghter plane. According to the Houston Post and Beaumont Enterprise, these ﬁghter planes were being tested in a corridor along the upper Texas Gulf Coast at about the time of the disturbances on 2 and 3 February. We have no information about 15 January and 24 March; however, the similarity of the felt reports and felt areas suggests these had the same origin. A plane breaking the sound barrier at a sufﬁcient height would produce a tremor over a large felt area accompanied by little audible noise following the pressure wave. Other sources mentioning these events include Comanche Peak Steam Electric System (1977), Nuttli (1979), Rea-

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BORGER — 20 JULY 1966 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

09:04:58.2 UTC 35.7 N 101.2 W V 36,000km2 mN 4.1; 3.8 mb 3.9; 4.3; 4.8

von Hake and Cloud (1968) von Hake and Cloud (1968) (This study) Davis and others (1989); Nuttli (1979) U.S. Coast and Geodetic Survey; International Seismological Centre; von Hake and Cloud (1968)

gor, Stover, and Algermissen (1982), South Texas Nuclear Project (1978), Varma (1975), and von Hake and Cloud (1968). Headlines

Beaumont Enterprise, 3 February 1966: “Mysterious Earth Tremors Are Felt over Wide Area of Texas, LA” Beaumont Enterprise, 25 March 1966: “Earth Tremors Felt Here Increase Phone Trafﬁc” Houston Post, 3 February 1966: “Tremors Blamed on F-111 Test” Houston Post, 4 February 1966: “Earth Tremors Felt in E Texas Coastal Areas”

Borger—20 July 1966 On 20 July 1966, at about 3:05 a.m. CST, a small shock occurred near Borger, Texas, producing intensity MMI V in Borger and Amarillo. According to von Hake and Cloud (1968): At Amarillo, an observer in the courthouse reported a chair moved 4 to 5 inches. Chairs also moved in the FAA Control Tower at the Municipal Airport. Observers thought a truck had hit the tower. Patients at the Amarillo Air Force Base Hospital were awakened. The Weather Bureau Station reported a barometer dial jumped at the time of the shock. Other observers noted that buildings creaked, windows rattled, and a rumbling noise accompanied the shock. Abrupt onset; swaying motion. At Borger . . . the earthquake was felt by nearly all. The press reported books fell from a shelf in one home, and that a loud rumble was heard. Others reported that buildings creaked and windows rattled. Abrupt onset; jarring motion. Duration, 3– 4 seconds.

Although a wide range of magnitudes is reported for this earthquake, the areal extent of the felt reports suggest that it was about 4.1. Shurbet (1969), a seismologist at Texas Tech University, noted several small seismic arrivals at World Wide Seismograph Station LUB (Lubbock, Texas) that he thought might be related to the Borger event: [The main shock] was preceded by several smaller earthquakes which were too small for location by the U.S.C.G.S. network. The Texas Technical College Observatory has

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Figure 9.20. Felt area map for the 20 July 1966 Borger and 15 February 1974 Perryton earthquakes. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded regions indicate major oil (dark shading) or gas (light shading) fields in Texas as mapped by Galloway and others (1983) and Kosters and others (1989) that were established prior to 1966. Lake Meredith is the solid black region west of Borger. Map and isoseismals revised using information from Davis, Pennington, and Carlson (1989).

located the smaller earthquakes from the general character of the seismograms rather than by the use of normal location procedure. They were in the same general area of the main earthquake as were aftershocks which seem to be still occurring from time to time.

Subsequently, Davis, Pennington, and Carlson (1989) reanalyzed these data and noted that most of the small events occurred during the daylight hours, espe188

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cially around 6 p.m. local time, suggesting that these might be blasts from road construction or from a nearby quarry. The cause of this 20 July 1966 earthquake is uncertain. Shurbet (1969; personal communications, 1983 and 1986) suggested it might have been induced by the damming of Lake Meredith at Sanford (see table 5.1), northwest of Borger: The [Sanford] dam was closed and water storage began on 28 January 1965 and Lake Meredith was about one-half ﬁlled by 15 July 1967. The dam itself contains about 15 million cubic yards of earth and it is reasonable to assume that the seismic activity described above is a result of the increased crustal load in the area.

Another possibility is that the earthquake was induced not by the ﬁlling of the dam but by oil and gas production. In support of this hypothesis is the fact that highest intensities occur at the edge of the Panhandle Field, which is among the largest oil and gas ﬁelds in Texas. However, the center of the felt area is somewhat south of both Lake Meredith and the Panhandle Field, closer to Amarillo. The most likely possibility is that its origin is tectonic. What is certain is that the cities within the felt area, including Sanford (see discussion of 20 June 1936 earthquake) had experienced several other earthquakes in the twentieth century prior to the construction of Sanford Dam. Other sources that mention the 1966 Borger earthquake include Comanche Peak Steam Electric System (1977), Docekal (1970), the International Seismological Centre, Northrop and Sanford (1972), Nuttli and Herrmann (1978), Pantex Facility (1975), Racine and Klouda (1980), Reagor, Stover, and Algermissen (1982), and von Hake (1977). Headlines

Amarillo Daily News, 20 June 1966: “That Dog under the Bed Was an Earthquake, Bub” Guymon Daily Herald, 20 June 1966: “Earth Tremor Shakes Area”

Kermit—14 August 1966 Residents in and around Kermit, Texas, felt a sharp earthquake at about 9:26 a.m. (15:26 UTC) on 14 August 1966. According to newspaper reports, many people mistook the earthquake for either a sonic boom or an explosion, and reported intensities in Kermit were at least as high as VI (Lander 1967): Several street signs were knocked down and panes of glass were broken. Police department evacuated the station when the building began shaking. A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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KERMIT — 14 AUGUST 1966 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

15:25:47 UTC 31.9 N 103.0 W VI 50,000km2 mb 3.4 mN 4.1; 4.3 mbLg 3.2 ML 2.8 Mcorr 3.3

Sanford and others (1978) von Hake and Cloud (1968) Docekal (1970) U.S. Coast and Geodetic Survey Davis and others (1989); Nuttli (1979) Gordon (1983) Sanford and others (1978) Rogers and Malkiel (1979)

The Odessa American stated: The brief tremor was reported to have cracked walls of a drive-in grocery store, the First Assembly of God Church, and several residences in Kermit. Police said reports of broken window glass and broken dishes were received.

The Lubbock Avalanche-Journal noted that the front door of one residence would not close after the earthquake and that: cracks appeared in the mortar of the grocery and a few cans fell from the shelves during the tremor. But, generally damage was minor, as reports of broken panes of glass, spilled coffee, broken jars of candy and plums and a downed trafﬁc sign came in to the Police station.

The various reports indicate that residents of several neighboring towns felt the earthquake but it produced no damage; for example, von Hake and Cloud (1968) reported that windows rattled in Loco Hills, New Mexico; and in Wink, Texas: Buildings creaked, loose objects rattled, and disturbed objects were observed. Very faint noises were heard; several were positive of ground movement.

The Odessa American reported that in Odessa the “earthquake was heard as a brief ‘boom.’” Other sources that mention this 1966 Kermit earthquake include Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), International Seismological Centre, Keller and others (1981), Racine and Klouda (1980), Reagor, Stover, and Algermissen (1982), Sanford and others (1980), Sanford and Toppozada (1974), Shurbet (1969), Stover and Coffman (1993), and von Hake (1977). Headlines

Lubbock Avalanche-Journal, 15 August 1966: “Kermit Shaken Up” Midland Reporter-Telegram, 15 August 1966: “Light Quake Jolts Kermit, Wink Areas” Odessa American, 15 August 1966: “Earthquake Rocks Kermit Early Sunday” 190

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EL PASO — 12 MAY 1969 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

Aftershocks:

08:26:19 UTC 31.8 N 106.4 W VI local ML 3.6; 3.9 mN 4.0 mb 4.5 (1) 08:49:16 UTC ML 3.3; 3.6 mb 4.3 (2) 08:51 UTC (3) 10:39 UTC

von Hake and Cloud (1971) von Hake and Cloud (1971) Davis and others (1989) ALQ—Albuquerque NM station; SNM—Socorro NM station Davis and others (1989) U.S. Coast and Geodetic Survey von Hake and Cloud (1971) ALQ; SNM U.S. Coast and Geodetic Survey von Hake and Cloud (1971) von Hake and Cloud (1971)

El Paso—12 May 1969 On the morning of 12 May 1969 a series of four earthquakes awakened numerous El Paso residents, although many mistook the earthquakes for sonic booms, dynamite, or Army maneuvers. Instrumental locations are available only for the ﬁrst two earthquakes. The El Paso Herald Post reported that in at least one home the largest shock caused minor damage, including cracks in a ceiling and a driveway; another woman said that her house shook so hard that her bed and her baby’s crib hit the wall. The shock caused some alarm and the El Paso police were swamped with calls, mostly from residents in the northeastern part of the city. A few people at Newman, about 32 km northeast of El Paso, also felt the tremor. Other sources that mention these earthquakes include Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), Gordon (1983), Lander (1969), Reagor, Stover, and Algermissen (1982), Toppozada and Sanford (1972), International Seismological Centre, and National Earthquake Information Service. Headlines

Austin Statesman, 12 May 1969: “Four Faint Quakes Felt in El Paso” El Paso Herald Post, 12 May 1969: “Four Earthquakes Jar El Paso”

Houston—12, 18, 19 June 1969 (Probable sonic booms) People near Houston’s Intercontinental Airport, Hobby Airport, in the Memorial section of Houston, and in La Porte, Texas, experienced a series of at least three shocks within a week in mid-June 1969. The Houston Post reported that the seismograph at Rice University recorded all three events and noted that Rice scientist Jean-Claude de Bremaecker analyzed these records and determined their magnitudes to be about 1.5–2.0. The tremors of 18 June were the strongest. One person felt a hard jolt and went outside, thinking that someone had hit the A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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HOUSTON — 12, 18, 19 JUNE 1969 (PROBABLE SONIC BOOMS) Origin times:

14:34 UTC 13:59 UTC 14:00 UTC

(12 June) (18 June) (19 June)

AMISTAD, NEW MEXICO — 12 JANUARY 1970 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

11:21:15.4 UTC 36.1 N 103.2 W VI (in New Mexico) 14,000km2 ML 4.2; 3.9; 3.3

mb 3.5

Toppozada and Sanford (1972) Coffman and von Hake (1972) Davis and others (1989) SLM—St. Louis MO station; ALQ—Albuquerque NM station; Sanford and others (1981) National Earthquake Information Service

house or that a large truck had hit a hole in the street. Another person felt three jolts, several seconds apart. A third person felt, more than heard, three series of three shocks, along with some change in air pressure. Another Houston resident stated that three shocks she felt on 19 June were almost certainly sonic booms, because she heard a jet shortly afterward. These reports and the timing of the shocks—all weekdays between 8:59 and 9:34 a.m. local time—suggest these events were sonic booms. Even so, they have been interpreted as earthquakes, and Yerkes and Castle (1976) even suggest they may have been caused by ﬂuid withdrawal from oil ﬁelds near Houston. Other sources mentioning these 1969 Houston events include Comanche Peak Steam Electric System (1977) and South Texas Nuclear Project (1978). Headlines

Austin American, 14 June 1969: “Small Tremor Hits Houston” Austin American, 20 June 1969: “Earthquakes May Be Tests” Houston Chronicle, 13 June 1969: “Tiny Tremor Measured Near Hobby” Houston Chronicle, 19 June 1969: “‘Earthquakes’ Could Be Seismic Shots in Gulf” Houston Post, 13 June 1969: “Houston Records First Earthquake” Houston Post, 19 June 1969: “Houston Has Second Tremor” Houston Post, 20 June 1969: “Earthquakes Here Bafﬂing, Not Dangerous, Expert Says”

Amistad, New Mexico—12 January 1970 At about 4:21 a.m. MST (11:21 UTC) on 12 January 1970, an earthquake was felt in several cities in New Mexico. At Amistad, “several feet of ceiling fell. Some

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TRAVIS PEAK — 3 FEBRUARY 1970 (PROBABLE SONIC BOOMS OR EXPLOSIONS) Origin time: Location:

Throughout the day 30.52 N 98.05 W

adobe bricks in a wall crumbled at the public school gymnasium, [it] awakened all [and produced] loud earth noises” (Coffman and von Hake 1972; Northrop and Sanford 1972). Plaster also fell in Nara Visa, New Mexico. Although the reports indicate that other places felt the earthquake, including Texline, Texas, neither the Amarillo Daily News nor the El Paso Times mentioned it. Other sources that mention this earthquake include Coffman, von Hake, and Stover (1982), Comanche Peak Steam Electric System (1977), Person (1970), Sanford, Olsen, and Jaksha (1981), Stover, Reagor, and Algermissen (1983), International Seismological Centre, and National Earthquake Information Service.

Travis Peak—3 February 1970 (Probable sonic booms or explosions) An article in the Austin American-Statesman on 3 February 1970 described how “unexplained vibrations and rumbling like distant thunder” shook the Travis Peak area of Lake Travis, 30 km northwest of Austin. Doors and windows rattled at different times, beginning at 10:30 a.m. CST and continuing until 11:30 p.m. CST. The newspaper ofﬁce received calls inquiring about the possibility of an earthquake. Nuttli (1979) assigned this event a location of 31 N, 97 W, a maximum intensity of IV, and a magnitude mN of 3.8. The felt reports are probably not due to earthquake activity but rather from explosions or sonic booms. Travis Peak is approximately 70 km south of Fort Hood, a large military reservation. Given favorable weather conditions, it is possible that conventional target practice or detonation of explosive weapons could be heard at that distance. Other sources mentioning these events are Comanche Peak Steam Electric System (1977) and Davis, Pennington, and Carlson (1989). Headline

Austin American-Statesman, 5 February 1970: “Earthquakes in Austin? Could Be”

Kermit—30 and 31 July 1971 Two earthquakes occurred in the Kermit area during late July 1971. Nuttli and Herrmann (1978) is the principal source that describes these events and assigns intensities of MMI III and MMI IV to the 30 July and 31 July quakes, respectively. Other sources that mention these 1971 Kermit earthquakes are Keller and oth-

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KERMIT — 30 AND 31 JULY 1971 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

01:45:51 UTC (July 30) 31.72 N 103.00 W — — mb 3.0 ML 4.5 mbLg 3.6 Mcorr 3.6 mN 3.0

Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

14:53:49 UTC (July 31) 31.70 N 103.06 W — — mb 3.4 ML 4.2 mbLg 3.2 Mcorr 3.8 mN 3.4

Reagor and others (1982)

U.S. Coast and Geodetic Survey Sanford and Toppozada (1974) Gordon (1983) Rogers and Malkiel (1979) Nuttli (1979) Reagor and others (1982)

U.S. Coast and Geodetic Survey Sanford and Toppozada (1974) Gordon (1983) Rogers and Malkiel (1979) Nuttli (1979)

NORTHEAST ARKANSAS — 1 OCTOBER 1971 Location: Maximum intensity: Felt area: Magnitudes assigned:

35.78 N 90.44 W V (in Arkansas) 140,000km2 mbLg 4.1 mN 4.1

Stover and others (1983) Stover and others (1983) Stover and others (1983) SLM—St. Louis MO station Nuttli (1979)

ers (1983), Reagor, Stover, and Algermissen (1982), and International Seismological Centre. Northeast Arkansas—1 October 1971 Although this earthquake’s epicenter was in northeastern Arkansas, Coffman and von Hake (1973a) state that it was felt in Nacogdoches, Texas, with intensity I–III. However, newspapers such as the Texarkana Gazette and the Troup Banner did not mention any felt reports from Texas. Davis, Pennington, and Carlson (1989) had no access to contemporary Nacogdoches newspapers and thus could not prove or disprove these reports. Another source mentioning this earthquake is Coffman, von Hake, and Stover (1982). Headline

Texarkana Gazette, 2 October 1971: “Light Tremor Shakes Northeast Arkansas”

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EL PASO — 9 AND 10 DECEMBER 1972 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

05:58 UTC 31.75 N 106.4 W IV 1,500km2 ML 3.0 mN 3.5

Davis and others (1989) Davis and others (1989) (This study) Sanford and Toppozada (1974) Davis and others (1989)

Origin times (aftershocks):

(a) 14:37:50 UTC (10 December) (b) 14:58:02 UTC (10 December) 31.75 N 106.4 W III 100km2 (a) & (b) ML 3.0; 2.7 (a) & (b) mN 3.0

Davis and others (1989) Davis and others (1989) Davis and others (1989) Sanford and Toppozada (1974) Davis and others (1989)

Location: Maximum intensity: Felt areas: Magnitudes assigned:

El Paso—9 and 10 December 1972 People in the vicinity of El Paso felt a series of three earthquakes during the weekend of 8–10 December 1972. The ﬁrst shock was the largest; there were felt reports from the Coronado area in northwestern El Paso to the town of Fabens, 50 km to the southeast. Police and local newspapers received numerous calls from concerned citizens. The El Paso Times reported that the earthquake saturated the seismometer at the University of Texas at El Paso, and the newspaper reported that one resident “said the earth shook and threw him out of bed. Another said the foundation of her house shook.” Many people thought that the tremors were caused by a sonic boom or explosion, but the news article noted that this was unlikely because no sound was heard during the event. The aftershocks of 10 December were felt only in a small area of southeastern El Paso, suggesting a shallow source. The El Paso Times reported that they occurred at about 6:30 a.m. and 7:00 a.m. (13:30 and 14:00 UTC); however, Sanford and Toppozada (1974) located two earthquakes instrumentally in El Paso at 14:37 and 14:58 UTC, and these are probably the same events. The locations reported above were assigned using the felt reports from the El Paso Times. Other sources that mention these 1972 El Paso earthquakes include Coffman and von Hake (1974) and Reagor, Stover, and Algermissen (1982). Headlines

El Paso Times, 9 December 1972: “Minor Tremor Reported in EP Area” El Paso Times, 10 December 1972: “EP Residents Shaken; Cause Unknown” El Paso Times, 11 December 1972: “More Early Morning Quakes Leave El Pasoans on Edge”

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Figure 9.21. Felt area map for the 2 January 1992 Rattlesnake Canyon and 9 December 1972 El Paso earthquakes. Roman numerals denote Modified Mercalli Intensities. For the 1972 earthquake, intensities were felt as MMI III within the indicated region except for MMI IV reports in a small area at the center. For 1992 earthquake, labeled towns show locations where news reports mention that citizens felt the event. Isoseismals for the 1972 earthquake are revised using information reported by Davis, Pennington, and Carlson (1989).

Fashing—25 December 1973 This event, which occurred on Christmas Eve local time, is the ﬁrst of several felt or instrumentally recorded earthquakes near the small town of Fashing, 80 km southeast of San Antonio. Coffman and von Hake (1975) state: Dec. 24. 20:46. Southwest of San Antonio, Texas. Intensity IV at Jend Rusell Ranch, about 27 kilometers west of Falls City. Intensity III at Port Arkansas [sic; probably

196

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FASHING — 25 DECEMBER 1973 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

02:46 UTC 28.82 N 98.20 W IV Local Mc 3.2; mN 3.3

Davis and others (1989) Coffman and von Hake (1975) Davis and others (1989) Davis and others (1989)

PERRYTON — 15 FEBRUARY 1974 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

13:33:50 UTC 36.38 N 100.52 W V 110,000km2 mb 4.5 mN 4.9; 4.5 mbLg 4.6

International Seismological Centre Coffman and Stover (1976) (This study) National Earthquake Information Service Davis and others (1989); Nuttli (1979) SLM—St. Louis MO station

Port Aransas], about 100 kilometers southeast of Falls City on the Gulf Coast. All other reports from towns in the region were negative.

Following an earthquake in 1983, Davis, Pennington, and Carlson (1989) undertook an intensity survey, and in the process they determined that the “Jend Rusell Ranch” is in fact the Fabian Jendrusch Ranch. It is unlikely that the earthquake was felt in Port Aransas, as it was not felt at other, closer towns. Several regional seismograph stations recorded this earthquake, and a number of people in a small area in and near Fashing felt it, reporting that windows and doors rattled. One woman noticed Christmas tree ornaments shaking, and a man saw a chandelier swinging. Other sources that mention the 1973 Fashing earthquake include Davis, Nyffenegger, and Frohlich (1995) and Pennington and others (1986). Perryton—15 February 1974 About 8:34 a.m. CST on 15 February 1974, an earthquake was felt by residents of parts of Texas, Oklahoma, and Kansas (see ﬁgure 9.20 accompanying description of 20 July 1966 earthquake). According to newspaper reports, one person described the quake as “a rumble . . . then things just started shaking.” Another man said, “It reminded me of when I was in Viet Nam. It felt like rockets coming in.” In Beaver, Oklahoma, the earthquake “shook the dickens” out of the county jail: “I was down there with another ofﬁcer and we both felt it plenty.” Several towns reported mild damage to plaster or buildings, including Beaver, Texhoma, and Woodward in Oklahoma and Liberal, Kansas. Coffman and Stover (1976) indicate that at Perryton a few glasses were broken and some walls

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DELAWARE BASIN — 1 AUGUST 1975 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

07:27:57 UTC 31.4 N 104.0 W II — mbLg 3.0; 3.2 mb 4.8

Coffman and Stover (1977) Coffman and Stover (1977) TUL— Tulsa OK station; Gordon (1983) National Earthquake Information Service

cracked and in Booker a “few cracks opened in walls,” while Darrouzett experienced “some cracking of plaster.” The report also mentions a “doubtful report of highway damage 1.6 km west of Briscoe [Texas] on Highway 83, 125 km southeast of [the] epicenter.” A notable feature of this earthquake is that information is available about the depth and focal mechanism. The seismograph at College, Alaska, reported a pP phase,7 which the International Seismological Centre used to calculate a depth of 24 km. However, Herrmann (1979) subsequently analyzed long-period Rayleigh and Love waves and obtained a depth of 10 km and a seismic moment of 4.0 x 1015 newton-meters. This mechanism contained both strike-slip and thrust components resulting from northwest-southeast compression; however, it may be unreliable because of the paucity of ﬁrst-motion data. Other sources that mention the 1974 Perryton earthquake include Comanche Peak Steam Electric System (1977), Gordon (1983), Nuttli and Herrmann (1978), Person (1974), Reagor, Stover, and Algermissen (1982), South Texas Nuclear Project (1978), Stover and Coffman (1993), International Seismological Centre, and National Earthquake Information Service. Headlines

Amarillo Daily News, 16 February 1974: “Quake Just a Rattler” Norman Transcript, 15 February 1974: “Quake Shakes Area” Tulsa Daily World, 16 February 1974: “Earthquakes Jolt Oklahoma Panhandle, 3 Other States” Wichita Falls Times, 15 February 1974: “Panhandle Quake Shakes 3 States” Woodward Daily Press, 15 February 1974: “Earth Tremor Rattles Two-state Area Today”

Delaware Basin—1 August 1975 This small earthquake occurred in West Texas and was felt with intensity II at Valentine (Coffman and Stover 1977). The location above, based on twelve seismograph stations, placed the epicenter somewhat northeast of Valentine in the Delaware Basin. Neither the El Paso Times nor the Odessa American men-

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KERMIT — 19 TO 25 JANUARY 1976 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

04:03:30.5 UTC (19 January) 31.90 N 103.09 W IV local Mcorr 3.2 mN 3.3 ML 3.5

mbLg 2.6 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

07:21:53 UTC (22 January) 31.84 N 103.09 W III local Mcorr 2.5; mN 3.0 ML 2.8; 2.0

Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

04:48:28 (25 January) 31.90 N 103.09 W V 2,000km2 Mcorr 3.2; mN 3.5 ML 3.9; 3.1 mbLg 3.3

Gordon (1983) Coffman and Stover (1978) Rogers and Malkiel (1979) Davis and others (1989) NEIS—National Earthquake Information Service; Coffman and Stover (1978) Gordon (1983)

International Seismological Centre Coffman and Stover (1978) (Sources as above) NEIS; Sanford and others (1978)

Gordon (1983) Coffman and Stover (1978) Davis and others (1989) (Sources as above) NEIS; Sanford and others (1978) Gordon (1983)

tioned the shock. Another source that mentions this earthquake is Reagor, Stover, and Algermissen (1982). Kermit—19 to 25 January 1976 Three earthquakes in January 1976 shook residents of the Kermit area in West Texas. Local newspapers mentioned the earthquakes but reported little about its felt effects. For all three shocks the highest intensities seem to have been reported by residents of Kermit itself. The third and largest shock was felt with lower intensities in Notrees, Texas; in Jal, New Mexico; in Ector and Winkler Counties in Texas; and in Lea County, New Mexico. Other sources that mention these 1976 Kermit earthquakes include Coffman, von Hake, and Stover (1982), Keller and others (1981), Person (1976), Reagor, Stover, and Algermissen (1982), Rogers and Malkiel (1979), and South Texas Nuclear Project (1978). Headlines

Odessa American, 20 January 1976: “Earthquake Felt in Kermit Area” Odessa American, 21 January 1976: “Minor Quakes Predicted to Hit Kermit Area”

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DURHAM, OKLAHOMA — 16 AND 19 APRIL 1976 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

18:59:46.1 UTC (16 April) 35.87 N 99.97 W IV 1,500km2 mbLg 3.4

TUL— Tulsa OK station Coffman and Stover (1978) Davis and others (1989) TUL

Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

04:42:43.9 UTC (19 April) 35.87 N 99.97 W IV 6,900km2 mbLg 3.5

TUL Coffman and Stover (1978) Davis and others (1989) TUL

Odessa American, 23 January 1976: “Earthquakes in Kermit Area Are Nothing New” Odessa American, 26 January 1976: “Another Quake Hits Kermit” Odessa American, 27 January 1976: “Kermit Tremor Activity ‘Could Be’ on Decline”

Durham, Oklahoma—16 and 19 April 1976 Two small earthquakes occurred in Oklahoma in a three-day period in April 1976; all reasonable locations place their epicenters along the Oklahoma-Texas border near the town of Durham, Oklahoma. The only felt report in Texas comes from Higgins; according to the Amarillo Daily News, “the quake rattled dishes at Higgins and may have been a little stronger at the Cities Service Plant 12 miles to the south, but no damage had been reported.” Other sources that mention these 1976 Oklahoma earthquakes include Gordon (1983), South Texas Nuclear Project (1978), Stover and others (1981), International Seismological Centre, and National Earthquake Information Service. Headlines

Amarillo Daily News, 20 April 1976: “Earthquake Rattles Panhandle Dishes” Woodward Daily Press, 19 April 1976: “Earthquakes Shake State”

Kermit—26 April 1977 For this small earthquake near Kermit, Coffman and Stover (1979) give the intensity as IV. Inexplicably, other sources reference their report while listing the intensity as V. Neither the Odessa American nor the El Paso Times mentions the tremor. Other sources that mention this earthquake include Gordon (1983), Keller and others (1981), Person (1977), Reagor, Stover, and Algermissen (1982), Rogers and Malkiel (1979), International Seismological Centre, and National Earthquake Information Service.

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KERMIT — 26 APRIL 1977 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

09:03:08 UTC 31.90 N 103.08 W IV — ML 3.3 mN 3.3 mbLg 2.7 Mcorr 2.8

Keller and others (1981) Coffman and Stover (1979) National Earthquake Information Service Davis and others (1989) Gordon (1983) Rogers and Malkiel (1979)

KERMIT — 2 MARCH 1978 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

10:04:53 UTC 31.55 N 102.56 W III — ML 3.5 mN 3.0; Mc 3.6

Gordon (1983) Stover and von Hake (1980) National Earthquake Information Service Davis and others (1989); Keller and others (1981)

Kermit—2 March 1978 Stover and von Hake (1980), who assigned an intensity III on the basis of a telephone report, provide the only known intensity information about this Kermit tremor. We have been unable to ﬁnd any local newspapers that mentioned the shock. Other sources that mention this 1978 Kermit earthquake include Gordon (1983), Reagor, Stover, and Algermissen (1982), South Texas Nuclear Project (1978), International Seismological Centre, and National Earthquake Information Service. Snyder—16 June 1978 The largest earthquake in a series apparently resulting from injection practices at Cogdell oil ﬁeld occurred shortly before 7 a.m. CST on 16 June 1978. The felt area (see ﬁgure 2.5) included such cities as Snyder, Lubbock, San Angelo, Abilene, and Big Spring. An aftershock (mbLg 3.4, TUL) occurred less than seven minutes later but was too small to be felt. Altogether, the International Seismological Centre lists eleven Snyder earthquakes, with the ﬁrst occurring on 7 June 1977 and the last on 28 November 1982 and including the earthquake of 17 June 1977, which the center apparently mislocated (see appendix C.6 in Davis, Pennington, and Carlson 1989). For the 16 June 1978 earthquake Stover and von Hake (1980) assigned several towns an intensity of V. At Snyder the earthquake cracked a window and caused a mirror to fall; one resident reported, “It just shook everything . . . It scared the daylights out of me.” At Carlsbad “hanging objects fell, small objects broke,” at

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SNYDER — 16 JUNE 1978 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

11:46:54 UTC 33.01 N 100.72 W V 100,000km2 mbLg 4.6 mN 4.5 mb 4.4; ML 5.3 mb 4.3

International Seismological Centre Stover and von Hake (1980) (This study) SLM—St. Louis MO station; TUL— Tulsa OK station Davis and others (1989) National Earthquake Information Service International Seismological Centre

Fluvanna there was “one broken window, hanging picture fell, light furniture shifted,” from Justiceburg came an “unconﬁrmed report of cracked plaster,” Peacock had a “few cracked windows,” and at Rotan “light furniture shifted.” Newspaper reports indicated the police in San Angelo “received about 30 calls from worried residents reporting the ﬂoors and walls of their homes shook and some furniture moved.” One ofﬁcer there claimed “the tremor moved his typewriter across the desk.” Police also received calls in Abilene and Big Spring, although one Big Spring resident described the tremor as “a little rattle in the headboard.” The shock awakened at least one resident of Colorado City. Lubbock was assigned an intensity of IV, although the Lubbock Avalanche-Journal reported that “the quake had no appreciable effect in Lubbock or Abilene.” The shock was also felt farther west in Andrews, Texas, and Hobbs, New Mexico. Voss and Herrmann (1980) studied the surface waves from this event and obtained a focal mechanism indicating normal faulting on a northeast-striking plane (see ﬁgure 9.10). They also determined a focal depth of 3.0 km, in good agreement with the depth of injection in the ﬁeld (about 2.1 km). They calculated a seismic moment of 6.5 x 1015 newton-meters and estimated a source fault radius of 1.3 km. Other sources that mention this 1978 Snyder earthquake include Coffman, von Hake, and Stover (1982), Davis and Pennington (1989), Dumas (1979), Gordon (1983), Harding (1981), Luza and Lawson (1979), Person (1978), Reagor, Stover, and Algermissen (1982), Stover and Coffman (1993), International Seismological Centre, and National Earthquake Information Service. Headlines

Amarillo Daily News, 17 June 1978: “Quake Rattles West Texas” Lubbock Avalanche-Journal, 16 June 1978: “Quake Causes Stir across West Texas” Lubbock Avalanche-Journal, 17 June 1978: “More Quakes Likely for Area, Tech Geosciences Expert Says” Odessa American, 17 June 1978: “Snyder Earthquake Shakes Little More than Nerves” Wichita Falls Times, 16 June 1978: “Earthquake Jars West Texas” 202

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SNYDER — 5 JULY 1979 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

01:05:01 UTC 33.01 N 100.86 W Heard, not felt — mbLg 2.7 Mc 2.5

International Seismological Centre

TUL— Tulsa OK station Davis and others (1989)

PAMPA — 9 JUNE 1980 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

22:37:10 UTC 35.50 N 101.05 W V 35,000km2 mN 4.3 mbLg 3.3 to 3.4

International Seismological Centre Stover and von Hake (1982) (This study) Davis and others (1989) TUL— Tulsa OK station

Snyder—5 July 1979 According to Stover and von Hake (1981) this small shock near the Cogdell oil ﬁeld was “heard but not felt at Snyder.” The earthquake was not mentioned in either the Amarillo Daily News or the Odessa American, although it was clearly recorded at several seismic stations. Other sources that mention this earthquake include Gordon (1983), International Seismological Centre, and Reagor, Stover, and Algermissen (1982). Pampa—9 June 1980 This earthquake, which was felt throughout much of the Texas Panhandle, was centered near Pampa, Texas. Stover and von Hake (1982) reported that it caused small cracks in walls in Pampa and produced intensity MMI IV in Lefors, Mobeetie, Skellytown, and White Deer. The Lubbock Avalanche-Journal noted that one resident of White Deer said, “The whole house popped. . . . [The resident] yelled a lot, it shook from one end of the house to the other.” Others at White Deer at ﬁrst mistook the earthquake for a sonic boom or explosion. Residents of Amarillo, Borger, Dawn, Memphis, Miami, Panhandle, and Vega also noticed the shock (see ﬁgure 2.5); various newspapers reported that it was felt in western Oklahoma but did not cite a speciﬁc location. The magnitude mN of 4.3, computed from the area of isoseismals, is somewhat larger than the mbLg of 3.4 determined by TUL and reported by the International Seismological Centre. A value of 4.3 seems more appropriate considering the large felt area; for example, compare this event with the 1982 Dalhart earthquake, for which TUL reported a magnitude mbLg of 3.8–3.9. The Dalhart earthquake had a felt area of only 8,200 km2 and a maximum intensity of III; furA NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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CENTER — 9 JUNE 1981 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

01:46:33.12 UTC 31.76 N 94.28 W III local mbLg 3.2 mN 3.0

Davis and others (1989) Davis and others (1989) Davis and others (1989) TUL— Tulsa OK station Davis and others (1989)

thermore, signiﬁcantly fewer stations reported arrivals for it to the International Seismological Centre. Other sources that mention the 1980 Pampa earthquake include Gordon (1983) and the National Earthquake Information Service. Headlines

Austin American-Statesman, 10 June 1980: “Tremor Rattles Panhandle” Lubbock Avalanche-Journal, 10 June 1980: “Earthquake Shakes Panhandle Area” Norman Transcript, 10 June 1980: “Quake Rattles Two States”

Center—9 June 1981 A small earthquake occurred on the evening of 8 June 1981 (local time) near the town of Center in East Texas. An article in the East Texas Light, a Center newspaper, stated that a person in southwestern Center felt a slight vibration lasting two or three seconds and that several people living west of Center near Arcadia reported that dishes and windows rattled. Although Stover and von Hake (1982) reported that this earthquake was felt “at the northern end of the Toledo Bend Reservoir” about 30 km northeast of Center, an unpublished intensity survey conducted in 1984 by University of Texas scientists could not conﬁrm that it was felt elsewhere than Center and immediately to the west. Several regional seismograph stations recorded the event, including a portable instrument located 55 km west of Center. The International Seismological Centre mislocated this event, apparently because it did not incorporate the reading from the portable instrument. Other sources that mention this earthquake include National Earthquake Information Service, International Seismological Centre, and Pennington and Carlson (1984). Headline

East Texas Light, 21 June 1981: “Tremor Rattles Area Houses”

Jacksonville—6 November 1981 This early-morning earthquake awakened many people near Jacksonville, Texas, and a few ran outside to determine the nature of the disturbance. Nearby seismographs operated by the University of Texas recorded two shocks about three minutes apart; the second, smaller tremor had a magnitude mbLg of 2.1.

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JACKSONVILLE — 6 NOVEMBER 1981 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

12:36:41.2 CST 31.95 N 95.92 W V 800km2 mbLg 3.3 mN 3.6 mbLg 3.2

Davis and others (1989) Davis and others (1989) Davis and others (1989) TUL— Tulsa OK station Davis and others (1989) OGO— Oklahoma Geophysical Laboratory

Figure 9.22. Felt area map for the 6 November 1981 Jacksonville earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded regions indicate major oil (dark shading) or gas (light shading) fields as mapped by Galloway and others (1983) and Kosters and others (1989) that were established prior to 1981. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1989).

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FORT STOCKTON — 4 JANUARY 1982 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

16:56:10 UTC 31.18 N 102.35 W III 2,500km2 mbLg 3.9

International Seismological Centre National Earthquake Information Service Davis and others (1989) TUL— Tulsa OK station

The Jacksonville Herald of 9 November 1981 published a felt report questionnaire for these events and obtained 125 responses. Residents of Jacksonville, Rusk, Maydelle, New Summerﬁeld, and Reklaw plainly felt the event. Several persons reported minor damage, including cracks in concrete patios and windows and a broken water pipe. In the epicentral area, large trees rustled, hanging lights swayed, telephone bells rang, objects on walls moved, and an antenna on a portable television waved back and forth. Dishes, windows, and doors rattled loudly and houses creaked. Noises heard ranged from a loud boom to a gradually increasing rumble. There are relatively large differences between the epicentral locations reported by various agencies for this earthquake. The location reported above was constrained by the numerous felt reports. Other sources that mention the 1981 Jacksonville earthquake include Pennington and Carlson (1984), Stover and others (1984), and International Seismological Centre. Fort Stockton—4 January 1982 Residents in the Fort Stockton area felt this earthquake, but according to newspaper reports it caused no damage. The El Paso Times noted “reports of the earthquake being felt as far as 20 miles north of Fort Stockton and 20 miles south.” Headlines

Corpus Christi Caller, 5 January 1982: “Fort Stockton Feels Quake” El Paso Times, 5 January 1982: “Earthquake Rattles Fort Stockton”

Dalhart—14 October 1982 A small earthquake shook the Dalhart area shortly before 8 a.m. local time on 14 October 1982. The National Earthquake Information Service lists the shock as felt with intensity III at Hartley, Texas, and at Amistad and Sedan, New Mexico, and it assigned intensity II to Dalhart and Texline, Texas. An Amarillo Daily News story suggests that the shaking may have been as strong as intensity III in Dalhart; in one house, a vase on a dresser and a rocking chair moved and dishes rattled in the cupboards. A custodian reported a crack in a parking lot. Several Dalhart residents heard a noise that “sounded like two or three sonic booms all at once.” Nearby at Hartley, the shock “rattled dishes and shook light ﬁxtures 206

T E X A S E A RT H Q UA K E S

DALHART — 14 OCTOBER 1982 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

12:52:45 UTC 36.05 N 102.53 W III 8,200km2 mbLg 3.8; 3.9 mN 3.6

International Seismological Centre National Earthquake Information Service Davis and others (1989) TUL— Tulsa OK station; National Earthquake Information Service Davis and others (1989)

SNYDER — 28 NOVEMBER 1982 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

02:36:48 UTC 32.92 N 100.85 W IV 32,000km2 mbLg 3.3 Mc 3.3; mN 3.9

International Seismological Centre National Earthquake Information Service Davis and others (1989) TUL— Tulsa OK station Davis and others (1989)

for about 20 seconds” but was not felt by all. The Amarillo Daily News also mentions that residents of Clayton, New Mexico, felt the shock. Headline

Amarillo Daily News, 15 October 1982: “Earthquake No Great Shake for Dalhart Folks”

Snyder—28 November 1982 There is no mention of this small earthquake in either the Amarillo Daily News or the Odessa American. All that is known of the intensity and felt area comes from the National Earthquake Information Service: “Felt (IV) at Snyder, (III) at O’Donnell and (II) at Dermott.” The International Seismological Centre reported a small (Mc 2.4) aftershock a few hours later at 05:42 UTC. The initial shock’s location suggests it was one of a series of earthquakes associated with ﬂuid injection in Cogdell oil ﬁeld. This earthquake is the only Cogdell-area earthquake known to be felt other than the somewhat larger shock of 16 June 1978; another shock on 5 July 1979 was heard at Snyder but not felt. Fashing—23 July 1983 This small earthquake occurred near the small town of Fashing, 80 km southeast of San Antonio. Pennington and others (1986) undertook an intensity survey and determined that the maximum intensity of MMI V was conﬁned to an area of 20 km2 or less centered 5 km northwest of Fashing. In the epicentral area, ground acceleration accompanying the event automatically shut down a boiler A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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FASHING — 23 JULY 1983 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

15:24:39 UTC 28.82 N 98.18 W V 200km2 mbLg 3.4 mN 3.6

Davis and others (1989) Davis and others (1989) Davis and others (1989) TUL— Tulsa OK station Davis and others (1989)

at the Warren Petroleum Company and caused a large refrigerator at the Jendrusch Ranch to rock back and forth. Farther from the epicenter one woman reported that her whole house lurched, while others heard a rumbling and a rattling of dishes and doors. A woman working outdoors 3 km northeast of the epicenter felt the shock. Many people in the area north of the epicenter heard a noise like thunder, although the sky was clear. Although most of the felt reports were conﬁned to an area of about 200 km2, a few people at greater distances from the epicenter may have felt the earthquake. There were secondhand reports that the shock was felt in Charlotte and Pleasanton, 50 and 35 km from the epicenter, respectively. At Gonzales, 100 km northeast of the epicenter, water in a kitchen sink sloshed over the sink’s sides. Stover (1987) also reported intensity III effects at Campbellton, DeWeesville, Schertz, and at the Tordillo Cattle Company Ranch 26 km west of Falls City. A small aftershock with magnitude of 2.1 occurred approximately seven hours after the main shock. It was felt within the initial shock’s epicentral area and recorded at stations in Austin and in Junction. The epicenter of this earthquake is only 38 km distant from the Choke Canyon Dam, which began impounding water in 1982. However, it is unlikely that this earthquake is reservoir-induced since several earthquakes occurred at apparently the same location in 1973–1975 (Davis, Nyffenegger, and Frohlich 1995) before the dam was constructed. Other sources that mention this 1983 Fashing earthquake include Stover (1987) and International Seismological Centre. Following the 1983 Fashing earthquake, Carlson (1984) and Davis, Pennington, and Carlson (1989) undertook a search for other earthquakes that might have occurred in the Fashing-Jourdanton-Pleasanton area. By inspecting seismograms from stations ATX (Austin, Texas), JCT (Junction, Texas), and LUB (Lubbock, Texas), they found 24 earthquakes that had occurred between 24 July 1973 and 5 January 1985 (see Davis, Pennington, and Carlson 1989, table C-1). Two of these earthquakes had been previously reported but were mislocated. Using arrival times from only four stations, a 24 June 1974 earthquake had been assigned an instrumental location near Palo Pinto, Texas, more than 440 km north of Fashing. A 28 March 1982 earthquake had been assigned a location near New Braunfels, Texas, some 120 km north of Fashing.

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Figure 9.23. Felt area map for the 23 July 1983 Fashing, 3 March 1984 Pleasanton, and 20 July 1991 Falls City earthquakes. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded regions indicate major oil (dark shading) or gas (light shading) fields as mapped by Galloway and others (1983) and Kosters and others (1989) that were established prior to 1983. Isoseismals for the 1983 and 1984 earthquakes are revised using information reported by Davis, Pennington, and Carlson (1989); 1991 information is from Olson and Frohlich (1992).

Pleasanton—3 March and 8 August 1984 On the evening of 2 March 1984 residents of the south Texas towns of Pleasanton, Jourdanton, Poteet, Leming, Christine, and McCoy felt an earthquake. The Pleasanton Express of 7 March published a questionnaire, and Pennington and others (1986) constructed an intensity map. The highest intensities were south of Pleasanton and east of Jourdanton in the area surrounding the Imogene oil ﬁeld. Several people became frightened and ran outside. One woman wrote: The terrible noise was our ﬁrst indication that something terrible was happening. My ﬁrst thought—an airplane had fallen on our house! My husband started running towards our (attached) garage—he said he thought one of the oil hauling trucks had run into our house! Pictures fell from our north ﬁreplace mantle and the wall seemed to sway! I actually for the ﬁrst time in my life became almost hysterical! My husband said it scared the “hell” out of him!

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PLEASANTON — 3 MARCH 1984 AND 8 AUGUST 1984 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

01:03:26 UTC 28.87 N 98.50 W V 1,300km2 mbLg 3.8; 3.9 mN 3.8

Davis and others (1989) Davis and others (1989) (This study) National Earthquake Information Service; TUL— Tulsa OK station Davis and others (1989)

Origin time (aftershock) Maximum intensity: Felt area: Magnitudes assigned:

01:58:25 UTC IV 100km2 ML 3.0 Mc 3.2; mN 3.3 mbLg 3.1

Davis and others (1989) Davis and others (1989) Davis and others (1989) National Earthquake Information Service Davis and others (1989) TUL

Origin time (aftershock)

01:31:28 UTC (8 August) Local mbLg 3.1

National Earthquake Information Service

Felt area: Magnitudes assigned:

National Earthquake Information Service TUL

At one residence the earthquake moved a cooking stove several inches and knocked objects out of cabinets. Merchandise fell from the shelves of a supermarket in Pleasanton, and small objects overturned in Jourdanton. The few reports of damage include cracked plaster, a widened crack in a driveway, and broken bottles. Several residents found that their telephones were inoperative for a few minutes after the shock; probably large numbers of people trying to make calls temporarily jammed the lines. An aftershock approximately one hour later was felt primarily near Pleasanton. One person reported that the later shock knocked a sliding screen door out of its track. There were other aftershocks during the following months. Apparently only two of these were felt: The ﬁrst occurred on 17 March 1984 and had a magnitude of Mc of only 1.6 (see Davis, Pennington, and Carlson 1989, table C-1); and the second occurred on 8 August and, with a magnitude mbLg of 3.1, was large enough to be located by the International Seismological Centre. Another source that mentions this earthquake is Davis, Nyffenegger, and Frohlich (1995). Valley View—18 September 1985 This small earthquake shook residents in Montague, Cooke, and Denton Counties in north-central Texas and was recorded by several regional seismograph stations. The National Earthquake Information Service assigned intensity MMI V

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VALLEY VIEW — 18 SEPTEMBER 1985 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

15:54:04 UTC 33.47 N 97.04 W V 700km2 mbLg 3.3 mN 3.4

TUL— Tulsa OK station National Earthquake Information Service Davis and others (1989) TUL; National Earthquake Information Service Davis and others (1989)

to the town of Sanger, IV to Valley View and Era, and III to Muenster and St. Jo. Local newspapers reported the shock was also felt at Pilot Point. The Denton Record-Chronicle reported that the tremor: sent people in Valley View and Pilot Point running into the streets, asking each other what had happened . . . [A woman east of Valley View] said Wednesday’s tremor set glasses to rattling in the Mountain Springs community center, and she’d heard one report of a man being shaken out of bed. “There was a rumble . . . then the whole house started shaking,” she said. “It felt like the whole house was going to fall down.”

The Dallas Morning News reported that the postmaster at Valley View assumed the event was a sonic boom, saying, “It hit twice. The building shook a little, and there was a loud boom.” The shock produced no damage. The epicenter of this event occurred in the vicinity of what is now Ray Roberts Lake; however, the shock was not reservoir-induced as impoundment for the lake did not begin until July 1987 (see table 5.1). It did occur during the construction of Ray Roberts Dam, which began in June 1982 and was completed in August 1986; thus it is conceivable that it was an explosion related to dam construction. Indeed, University of Texas seismologist Toshimatsu Matsumoto noted a report of a mushroom-like cloud in the area, which might indicate blasting. However, both the magnitude of the event as well as the character of seismograms recorded at several Oklahoma stations and analyzed by Jim Lawson, an Oklahoma seismologist, suggest that the shock was an earthquake and not a blast. Another source that mentions this earthquake is the International Seismological Centre. Headlines

Dallas Morning News, 21 September 1985: “Small Quake Spawned Tremors in North Texas, Scientist Says” Denton Record-Chronicle, 20 September 1985: “Tremor Sends Valley View, Pilot Point Residents Into Streets” Fort Worth Star-Telegram, 21 September 1985: “Tremors Hit Texas Tuesday” Gainesville Daily Register, 20 November 1985: “Cooke County Quake a History Making Event”

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MICHOACAN, MEXICO — 19 SEPTEMBER 1985 Origin time: Location: Magnitudes assigned:

13:17:50.1 UTC 18.54 N 102.32 W MW 8.0 MS 8.1

International Seismological Centre Dziewonski and others (1986) National Earthquake Information Service

Michoacan, Mexico—19 September 1985 This major earthquake occurred off the coast of Mexico but produced the most serious damage about 400 km away in Mexico City. The National Earthquake Information Service reported: At least 9,500 people were killed, about 30,000 were injured, more than 100,000 people were left homeless, and severe damage was caused in parts of Mexico City and in several states of Central Mexico. According to some sources, the death toll from this earthquake may be as high as 35,000. It is estimated that the earthquake seriously affected an area of approximately 825,000 km2, caused between $3 billion and $4 billion of damage, and was felt by almost 20 million people. 412 buildings collapsed and another 3,124 were seriously damaged in Mexico City . . . A large percentage of the buildings which were damaged were between 8 and 18 stories high, indicating possible resonance effects with dominant two-second period horizontal ground accelerations which were recorded in the area.

The report noted that the earthquake produced landslides that caused damage in several areas. At several cities along Mexico’s Paciﬁc coast it also generated a tidal wave that reached heights as great as 3 meters, causing some damage. Because of the quake’s size and severity it received considerable attention from the scientiﬁc community; for example, a special issue of Geophysical Research Letters was devoted to it (Kanamori and Ruff 1986). Newspaper articles document that residents of several cities in southeast Texas felt this earthquake; its high death toll thus makes it the most devastating earthquake felt in Texas history. The Dallas Morning News reported that in McAllen the vibrations were felt in the eighteen-story State Bank. The Corpus Christi Caller stated that the bridge master at the Corpus Christi Tule Lake Lift Bridge became frightened when the bridge started to shake: “[The vibrations] shook the whole control house.” In the Houston-Galveston area many people on the upper ﬂoors of buildings felt the shock. The only report of damage in Texas is from Houston, where the Houston Post reported that a coffeepot crashed to the ﬂoor. Newspapers reported various other long-period effects in Texas. The Daily Texan reported that “an oil company in Port Arthur said that four scales in their laboratory showed slight movement,” and the Austin American-Statesman reported movement in tanks at several petroleum reﬁneries in Pasadena, east of

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Houston. The Fort Worth Star-Telegram mentioned that vibrations in tools used to make crystals slowed production at the Texas Instruments plant in Sherman. According to the Dallas Morning News, elevators in a few tall buildings in Houston made noises and acted strangely. Very prominent among the long-period effects of the earthquake were seiches, especially in swimming pools, observed in Texas, New Mexico, Colorado, and Idaho. The El Paso Times reported that the seismic observatory at the University of Texas at El Paso received numerous phone calls about seiches; one resident reported the water washed over the sides of his pool. The San Antonio Express-News reported swimming pool seiches and the swaying of tree branches at Beaumont, Houston, Laredo, McAllen, Padre Island, Port Arthur, and Poteet: the Corpus Christi Caller reported that swimming pools sloshed in Alice, Bishop, Corpus Christi, Driscoll, Ingleside, and Portland. The Dallas Morning News noted that water spilled from the aquatic life swim tanks at the Marine Science Institute in Corpus Christi. The Houston Post noted that the earthquake produced a “sudden swell on East Galveston Bay that threw wading ﬁshermen off balance.” Headlines

Austin American-Statesman, 20 September 1985: “South Texans Notice Tremors in Earthquake” Austin Daily Texan, 20 September 1985: “Texans Feel Earthquake Vibrations” Corpus Christi Caller, 20 September 1985: “City Pools Show Wave of Shock” Dallas Morning News, 20 September 1985: “Tremors from Quake Cause Little Alarm in Texas” El Paso Times, 20 September 1985: “Pool Sloshes Told Expert Earthquake was ‘Huge’” Fort Worth Star-Telegram, 20 September 1985: “Texans See Buildings Jar, Water Slosh” Houston Post, 20 September 1985: “Houstonians Rattled by Quake’s Tremors” Odessa American, 20 September 1985: “Houston Buildings Rattle from Quake” San Antonio Express News, 20 September 1985: “Quake-caused Shock Wave Swamps 3 Cities” San Antonio Express News, 20 September 1985: “Quake Shock Waves Felt Throughout South, East Texas”

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SILVER — 30 JANUARY 1986 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

22:26:37 UTC 32.02 N 100.70 W IV Local mbLg 3.3; 3.1

International Seismological Centre National Earthquake Information Service National Earthquake Information Service; TUL— Tulsa OK station

Silver—30 January 1986 The National Earthquake Information Service reported that this earthquake in Coke County was felt with intensity MMI IV at Silver and MMI II at Robert Lee. Both the epicenter and felt reports center on the E. V. Spence Reservoir, suggesting a possible causal relationship. Robert Lee Dam, which impounds the E. V. Spence Reservoir, was completed in 1969 and has a water depth of 42 meters above streambed. We have not found any newspaper stories describing felt reports from this earthquake. Waco—3 November 1986 (Probable explosions) Residents of Waco and neighboring communities in McLennan and Falls Counties felt a series of four shocks around 7 a.m. (local time). The Waco TribuneHerald stated: Waco Police began receiving reports of the tremor shortly after 7 a.m., Curtin [director of the Waco-McLennan County Emergency Management Center] said. According to the majority of reports received, he said, there was one fairly strong tremor around 7 a.m., followed by two lighter tremors and another fairly strong tremor at 7:09 a.m. [One Waco resident reported the shaking] “was enough to rattle the windows and literally move the furniture.”

The shocks probably resulted from bomb tests. The 23rd Tactical Fighter Wing from England Air Force Base in Louisiana conducted bombing training using 500-pound bombs at nearby Fort Hood from 6:30 a.m. to 7:30 a.m. local time. Although a Fort Hood spokesman stated that the bombs caused the shaking, some residents still believed a small earthquake occurred. Their stated reasons were: ﬁrst, no shocks appear to have been felt prior to 7:00 a.m., although the bombing began around 6:30 a.m. Second, one resident who had previously felt both earthquakes and bombs declared that the shaking was more like that of an earthquake. Finally, the large felt area of at least 500 km2 is suggestive of an earth tremor. However, no events at that time were identiﬁable on seismograms from stations in the Texas Panhandle. Although it is possible that a small

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FALLS CITY — 20 JULY 1991 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

23:38:17 UTC 29.0 N 98.0 W IV 110km2 (Intensity IV) mbLg 3.6; 3.4

Olson and Frohlich (1992) National Earthquake Information Service (This study) National Earthquake Information Service; TUL— Tulsa OK station

tremor produced the shaking, it is more likely that the largest bombs were noticed around 7 a.m. Headline

Waco Tribune-Herald, 4 November 1986: “Air Force— or Quake?—Rattles Houses”

Rotan—15 January 1987 (Probable sonic booms) On 16 January 1987 United Press International released a small story about possible earthquakes in the town of Rotan, approximately 80 km northwest of Abilene. Three tremors occurred between 5:30 a.m. and 9:30 a.m. CST. According to the article, no damage and no injuries ensued, although “some schoolchildren were upset.” The county sheriff theorized that the tremors were earthquakes, based on the proximity of Rotan to Snyder, site of several earthquakes (for example, see ﬁgure 2.5 and description of 16 June 1978 earthquake). Further, “a check with nearby Dyess Air Force Base in Abilene indicated that no B-1B bombers, which could have caused a sonic boom, were ﬂying.” Although it is possible the tremors were tiny earthquakes, it is more likely they were probably sonic booms (Davis, Pennington, and Carlson 1989). The seismograph at station LUB in Lubbock (150 km distant) did not record any motion, nor did the Oklahoma Geological Survey locate any earthquake in Texas on this date. Headline

UPI, 16 January 1987: “Dateline: Rotan, Texas”

Falls City—20 July 1991 This small Gulf Coast earthquake occurred near the towns of Falls City and Hobson. Subsequently Olson and Frohlich (1992) conducted personal interviews and collected felt report responses from a questionnaire in the Karnes Citation (see ﬁgure 9.23 accompanying description of 7 July 1983 earthquake). Many persons reported hearing explosive sounds and thought they had experienced a sonic boom. However, the rarity of Gulf Coast earthquakes and the proximity of the felt area to producing oil and gas ﬁelds suggest that it was induced. Other sources that mention this earthquake include Davis, Nyffenegger, and Frohlich (1995), Davis and Frohlich (1995), and International Seismological Centre.

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RATTLESNAKE CANYON, NEW MEXICO –TEXAS BORDER — 2 JANUARY 1992 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

11:45:36 UTC 32.36 N 102.97 W V 440,000km2 mb 4.6; 4.5; 4.3

mbLg 5.0

International Seismological Centre National Earthquake Information Service (This study) National Earthquake Information Service; International Seismological Centre; NAO–NORSAR Sweden seismic array TUL— Tulsa OK station

Headline

Karnes Citation, 24 July 1991: “Earthquake...An Earth Shaking Experience for Karnes County”

Rattlesnake Canyon, New Mexico–Texas Border—2 January 1992 This early-morning earthquake produced intensities of MMI IV to V over a wide area along the Texas–New Mexico border (for felt area map see ﬁgure 9.21 accompanying discussion of 9 December 1972 earthquake). Despite the large felt area, the only damage speciﬁcally reported by the Dallas Morning News was a broken needle on the McDonald Observatory seismograph. In Andrews, 50 km east of the epicenter, the shock awakened and alarmed sleepers. In Kermit, the same distance to the south, the Midland Reporter Telegram said one resident reported that her mobile home shook: “It felt as though someone was outside just rocking the trailer back and forth . . . everything was rattling.” The Houston Chronicle published a similar report from Midland (100 km southeast): “I thought it was a buffalo rubbing up against my mobile home.” Sixty kilometers to the northeast in Seminole, one man thought at ﬁrst there had been an explosion in a nearby gas plant when “the couch moved about half an inch from the wall with me in it.” The El Paso Times noted that tours of nearby Carlsbad Caverns (140 km southwest of the epicenter) were not delayed by the quake. The El Paso Times did report that the proximity of the epicenter to a proposed nuclear waste repository generated concern among the project’s opponents. Shortly after the earthquake a spokesperson for the Waste Isolation Pilot Program said that engineers for the plant were authorized to return to the site’s underground tunnels by mid-afternoon of the day following the earthquake. The following week the Department of Energy Project Site manager reported that inspection of the site revealed no damage to any of its structures. In spite of the small size of this earthquake, Sanford and others (1993) constructed a focal mechanism from ﬁrst motions (see ﬁgure 9.10). This indicated the event was a nearly pure thrust with an east-west compression axis.

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JOURDANTON — 10 AUGUST 1992 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

01:57:47 UTC 28.92 N 98.54 W V local mbLg 2.8

(This study) (This study) (This study) National Earthquake Information Service

Headlines

Albuquerque Journal, 15 April 1995: “Quake Shakes Up Concerns on WIPP” Atlanta Journal and Constitution, 2 January 1992: “Earthquake Shakes Texas, New Mexico” Austin American-Statesman, 3 January 1992: “Early Morning Quake Shakes West Texas, Eastern New Mexico” Dallas Morning News, 3 January 1992: “Quake Rattles Parts of NM, West Texas / Tremor Spurs Concern About Nuclear Waste Plan, Oil Drilling” Dallas Morning News, 6 January 1992: “Astrologer Takes a Look at the Stars and the Future” El Paso Times, 3 January 1992: “Earthquake Rattles NM, Texas” El Paso Times, 3 January 1992: “WIPP Protesters Warn of Danger” El Paso Times, 4 January 1992: “WIPP Work Continues After Quake” El Paso Times, 7 January 1992: “Minor Quake Didn’t Affect WIPP, Ofﬁcials Say” Houston Chronicle, 3 January 1992: “Small Quake Jolts West Texas; No Injuries or Damage Reported in Mostly Desolate Area” Midland Reporter Telegram, 3 January 1992: “Rare Quake Jolts Area” New York Times, 3 January 1992: “Light Earthquake Sends Tremor through Texas and New Mexico” San Angelo Standard Times, 3 January 1992: “Quake Rattles W. Texas” San Angelo Standard Times, 3 January 1992: “Tremor Leaves Many Slumbers Intact” St. Petersburg Times, 3 January 1992: “Flooded Texas Rattled by Quake”

Jourdanton—10 August 1992 This small earthquake occurred in Atascosa County close to the epicenter of the 3 March 1984 Pleasanton earthquake; it was probably quite shallow as it was felt fairly strongly in Jourdanton but apparently not in nearby Pleasanton, less than 8 km away. The strongest felt effects were very localized. According to the Pleasanton Express:

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FASHING — 9 APRIL 1993 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

12:29:19 UTC 28.87 N 98.50 W VI 5,000km2 mbLg 4.3 mb 4.1

(This study) Davis and others (1995) (This study) National Earthquake Information Service International Seismological Centre

residents in Encino and Atascosa Estates subdivisions sustained the greatest impact from the tremor. The community’s convenience stores reported feeling the quake and ranchers said their animals were upset by the tremors . . . [Jourdanton’s Water Superintendent] Reynolds said that although none of the city structures sustained damage, that was not the case with the city water system. Monday morning found Reynolds and Jourdanton’s Water Department crews out trying to repair breaks in one 2-inch water main, one 4-inch water main and in 3 one-inch water mains. While some residents reported small cracks in stone, rock, brick or concrete, only one person reported substantial structural damage to a residence. Reynolds said one Jourdanton resident had a rude shock when his bedroom dropped at least one inch during the quake.

The article also suggested that other quakes occurred earlier that summer: “This is at least the second quake in about a month,” said [Jourdanton Chief of Police] Richter. “About a month ago I was talking to my wife on the telephone when the whole house shook. She thought it was a big truck passing when I told her but there was no big truck around. It was a small earthquake.”

While the National Earthquake Information Service did not report the alleged earlier events, it is quite possible that they did occur. Another source that mentions this earthquake is Davis, Nyffenegger, and Frohlich (1995). Headline

Pleasanton Express, 12 August 1992: “Quake Shakes Jourdanton Community”

Fashing—9 April 1993 This earthquake, the largest in southeastern Texas in historic times, occurred near the town of Fashing, at or very near the location of the 23 July 1983 earthquake. Davis, Nyffenegger, and Frohlich (1995) prepared an intensity map after interviewing local residents and analyzing results from questionnaires published in the Pleasanton Express and the Karnes City Citation. They found that the highest intensities were very localized, with the intensities MMI IV, V, and VI areas covering 2,100, 140, and 16 km2, respectively. Minor damage occurred at the Warren Petroleum Plant, which processes natural gas from the Fashing gas ﬁeld. Several reinforced concrete foundation blocks and one pipe connection cracked or broke. In places the horizontal movement was at least several centi-

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Figure 9.24. Felt area map for the 9 April 1993 Fashing earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded regions indicate major oil (dark shading) or gas (light shading) fields as mapped by Galloway and others (1983) and Kosters and others (1989) that were established prior to 1983. Map and isoseismals are revised using information reported by Davis, Pennington, and Carlson (1995).

meters, causing a cracked nipple, a broken anchor bolt, and stretched steel bolts. The ground motion triggered an emergency shutdown of the plant, but there were no gas leaks. Most of the damage to surrounding residences was minor. Initial newspaper reports indicated the tremor shook a house in Campbellton off its foundation; however, inspection of the site indicated that the foundation was initially not very sturdy. The San Antonio Express-News reported that in the town of Peggy some at ﬁrst thought the shaking was an explosion at the gas plant. Items fell from shelves at other nearby sites, but there were no reports of serious damage. A peculiar feature of this shock is that it attracted the notice of the Branch Davidians. These were members of a religious group who were under siege by the Federal Bureau of Investigation near Waco, Texas, at the time of the earth-

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JOURDANTON — 16 MAY 1993 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

15:30:19 UTC 28.9 N 98.50 W IV 300km2 mbLg 3.0

(This study) National Earthquake Information Service (This study) National Earthquake Information Service

quake and who believed the quake had religious signiﬁcance (see chapter 2 for quotes from newspaper articles about this). Headlines

Austin American-Statesman, 10 April 1993: “South Texas Quake Causes Gas Leaks, Frayed Nerves” Corpus Christi Caller, 10 April 1993: “Earthquake Jolts South Texas Area, Closes Plant; No Injuries Reported” Pleasanton Express, 14 April 1993: “Earthquake Hits Atascosa County” Progress, 14 April 1993: “Atascosa Earthquake Felt in Live Oak” San Antonio Express-News, 10 April 1993: “Light Quake Rattles South Texas Towns” San Antonio Express-News, 10 April 1993: “Rattled South Texans Bafﬂed by the Little One” UPI, 12 April 1993: “FBI Says Cult Now Wants More Direct Sign From God” Washington Post, 15 April 1993: “Koresh Says Manuscript Will End Waco Standoff”

Jourdanton—16 May 1993 Just a little over a month after the 9 April 1993 Fashing earthquake, a smaller tremor located farther to the west shook the towns of Jourdanton, Pleasanton, and Poteet. Most of the people who felt the shaking also had experienced the Fashing quake and thus recognized the event as an earthquake. Nevertheless, the shock frightened some Jourdanton residents; the San Antonio Express-News quoted one individual: “It really scared some people . . . It really came unglued on some of us out here.” According to the Austin American-Statesman, “One ofﬁcer, who was in his car during the quake, reported that his vehicle shook so badly he thought a child was jumping on his fender.” The Pleasanton Express noted that “the city of Jourdanton could ﬁnd no evidence of broken lines nor structural damage as a result of the temblor Sunday.” Other sources that mention the 1993 Jourdanton earthquake include Davis, Nyffenegger, and Frohlich (1995) and International Seismological Centre. Headlines

San Antonio Express-News, 17 May 1993: “Second Quake Rattles Jourdanton Vicinity” 220

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AMISTAD, NEW MEXICO — 29 SEPTEMBER AND 30 NOVEMBER 1993 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned: Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

02:01:19 UTC (29 September) 35.90 N 103.03 W III Local mbLg 3.3 03:07:32 UTC (30 November) 35.86 N 103.03 W IV 9,700km2 mbLg 3.3 mDUR 3.3

International Seismological Centre National Earthquake Information Service National Earthquake Information Service

National Earthquake Information Service National Earthquake Information Service (This study) National Earthquake Information Service SNM—Soccoro NM station

Austin American-Statesman, 17 May 1993: “South Texas Shaken by Second Quake” Pleasanton Express, 19 May 1993: “Earthquake: Another Hits Atascosa County”

Amistad, New Mexico—29 September and 30 November 1993 These two small earthquakes occurred near the Texas–New Mexico border near the far northwest section of the Texas Panhandle. The National Earthquake Information Service listed the ﬁrst shock as only being felt in Amistad, New Mexico; however, it reported that the 30 November earthquake was felt in several locations, including MMI III “10 miles north of Sunray, TX.” We have not been able to locate any original felt reports for these earthquakes. Hallettsville—4 January 1995 At 1:46 UTC on 4 January 1995 (7:46 p.m. CDT on 3 January) a small earthquake occurred in the Texas Gulf Coast between Houston and San Antonio. The Preliminary Determination of Epicenters reported that the earthquake shook with intensity IV at Shiner and was also felt in the Hallettsville area in the center of Lavaca County. According to the Fort Worth Star-Telegram: one Lavaca homeowner thought his grandchildren, who were jumping on a bed, had started pouncing on the ﬂoor of his century-old farmhouse. Another family reported that their doorbell rang spontaneously.

Although the San Antonio Express-News stated that “there was absolutely no damage at all reported,” newspaper stories in the Victoria Advocate and the Fort Worth Star-Telegram indicated that some local residents remembered the Brenham explosion of 7 April 1992 and worried at ﬁrst that the tremor was a similar A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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HALLETTSVILLE — 4 JANUARY 1995 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

01:46:14 UTC 29.45 N 96.95 W IV Local mbLg 2.7

National Earthquake Information Service National Earthquake Information Service National Earthquake Information Service

ALPINE — 14 APRIL 1995 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

00:32:56 UTC 30.29 N 103.32 W VI 760,000km2 MW 5.7 MS 5.7

International Seismological Centre National Earthquake Information Service (This study) Dziewonski and others (1996) National Earthquake Information Service

explosion. At least one family went outside to look for the glow of an explosion or ﬁre. Headlines

Austin American-Statesman, 6 January 1995: “Mild Quake Might Have Rattled Lavaca County” Fort Worth Star-Telegram, 6 January 1995: “Mild Earthquake Jolts South Texas County” San Antonio Express-News, 5 January 1995: “Data about Possible Lavaca Quake Remains Shaky” Victoria Advocate, 5 January 1995: “All Shook Up! Minor Tremor Rattles Hallettsville”

Alpine—14 April 1995 This West Texas earthquake is the second largest in Texas history, being only slightly smaller than the Valentine earthquake of 16 August 1931. Because of its unusual size (for Texas) and location it attracted the attention of seismologists far from Texas borders. It is the only Texas earthquake for which the Harvard group has reported a mechanism in its Centroid Moment Tensor (CMT) catalog (Dziewonski, Ekstrom, and Salganik 1996; see ﬁgure 9.10), a compilation that began in 1977. Furthermore, at least four other scientiﬁc investigations have analyzed its seismic waves to investigate the structure of the earth’s crust and mantle beneath the United States (Melbourne and Helmberger 1998; Das and Nolet 1998; Xie 1998; and Rodgers and Bhattacharyya 2001). The epicenter was situated somewhat to the southeast of Alpine, Texas, where it generated intensities high enough to cause general alarm and minor damage. The Albuquerque Journal and the Los Angeles Times reported that bro222

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Figure 9.25. Felt area map for the 14 April 1995 Alpine earthquake. Roman numerals denote Modified Mercalli Intensities. For town names in higherintensity areas see figure 9.27.

ken gas mains caused several small ﬁres. Other newspaper articles indicated that in Alpine there were cracked walls, smashed dishes, broken water and gas lines, and a few minor injuries; for quotes from several of these newspaper articles see chapter 2. The earthquake dislodged several suspended ceilings at Sul Ross State University near Alpine and caused a pendulum grandfather clock to stop keeping time. Several newspapers reported that the earthquake caused a landslide on Cathedral Mountain (elevation 6,860 feet, about 20 km south of Alpine), where the shaking knocked loose a portion of the mountain’s top. The San Jose Mercury News quoted an ofﬁcer of the Texas Department of Public Safety who stated, “It looked like the mountain had been karate-chopped.” The Pecos Enterprise also reported that “one Marfa eye-witness saw dust coming from the base of the Davis Mountains following the quake, as if they were settling back into place.” Newspapers reported that minor damage occurred at several other towns, inA NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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cluding Pecos (125 km to the northeast), Fort Davis (60 km to the northwest), and Marathon (10 km east). Plaster cracked and windows broke in some homes in Pecos, and the shaking was severe enough there that residents jammed the police department’s telephone for about thirty minutes after the shock. The Pecos Enterprise reported that “Christians observing the cruciﬁxion of Jesus Christ and his resurrection thought Thursday night they were re-living that event.” Windows cracked in Crane, 155 km to the northeast. Minor damage was also reported in Ozona (210 km east) and even as far north as Roswell, New Mexico (360 km distant), where a ﬁre hydrant broke. As with the 1992 Rattlesnake Canyon earthquake, the Alpine event broke the needle of the seismometer at the McDonald Observatory, about 80 km northwest of the earthquake. Most of far West Texas experienced intensities of IV or higher. In Presidio (130 km southwest), United Press International reported that the shock “startled some 500 people attending a Maundy Thursday service at St. Teresa Catholic Church.” The Austin American-Statesman reported that near Study Butte (105 km south) the shock was “scary” and knocked jars off shelves. The San Angelo Standard Times reported that in San Angelo, 305 km northeast, the shock awakened sleepers and scared the “bejabbers” out of them. City police and ﬁre dispatchers there received several hundred calls that jammed the telephone lines. Citizens over much of the state of Texas felt the Alpine earthquake. United Press International noted that students at San Antonio College in San Antonio (505 km east) “said they felt the quake and could see television sets shaking and chalk falling off chalk trays on blackboards.” However the Austin AmericanStatesman reported that while the shock was felt in the air control tower at San Antonio International Airport, it was not felt on the ground. People in tall buildings felt the earthquake in Austin and Amarillo (both 540 km distant), Dallas (680 km distant), and even in Oklahoma City, Oklahoma, nearly 800 km away. Other effects in the days following are less clearly related to the earthquake. The Pecos Enterprise reported that on 18 April a gas pipeline explosion near Verhalen (100 km north of the epicenter) blocked trafﬁc for almost three hours: Firemen from Pecos and Balmorhea were called to the scene, but could only stand by and watch for nearly an hour as gas roared out of the pipeline with the sound of a jet engine. Flames shot as high as 50 feet in the air and could be seen as far away as the south side of Pecos. The force of the explosion set several nearby utility poles on ﬁre, downed electric lines running overhead, and created a line of brush ﬁres in a ﬁeld just to the east of the blast site. 224

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There was speculation that a gas leak from the earthquake may have been responsible for the blast. In a 1997 article the Pecos Enterprise also noted that one Verhalen man wondered if cracks that appeared in the ground a couple of years after the earthquake could have been caused by the shock; however, the article explained that Kevin Urbanczyk of Sul Ross State University believed evaporites were a more likely explanation. Because earthquakes of this size are a rarity in Texas, it generated more than its share of amusing anecdotes and business opportunities. According to an interview on The Nashville Network (TNN), country and western music star Junior Brown has his guitars custom made in Alpine, and he was in that town at the time of the quake. He had just picked up his famous “Big Red” guitar and was testing it out when the walls started shaking. According to the San Angelo Standard Times, another shop in Alpine used the opportunity to market mementos of the quake: The print shop ﬁlled an order for a local retailer Friday morning for 200 shirts bearing the words, “I survived the Quake of ‘95.” At the bottom of the shirt were the words: “5.6 by volume,” in reference to preliminary estimates of the quake’s magnitude . . . The ﬁrst 200 shirts sold out before noon.

Finally, the Ste. Genevieve Winery in Fort Stockton also sold a limited run of an “Earthquake Red” wine (see ﬁgure 9.26). According to the label on the back of the bottle: At 7:33 on the evening of April 13, 1995, something unheard of in the state of Texas happened; an earthquake of magnitude 5.6 struck just a few scant miles from our vineyards and winery. In the ensuing mayhem, quite a few barrels of our Cabernet Franc were inexplicably blended with several hundred gallons of aged Cabernet Sauvignon. Recognizing the providential signiﬁcance of this blending, we promptly bottled it. Look for strong earthy overtones in this fortuitously ﬂavorful red.

We the authors sampled this earth-shaking blend and found it tasty and without any major faults, though it was not of the magnitude of some California wines. Headlines

Albuquerque Journal, 15 April 1995: “Quake Shakes Up Concerns on WIPP” Arizona Republic, 15 April 1995: “Quake Shakes Up Texans / Temblor Is First in State Since 1931” Atlanta Journal and Constitution, 14 April 1995: “Biggest Quake in 60 Years Surprises West Texas Area” A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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Figure 9.26. Following the 14 April 1995 earthquake in West Texas, the Ste. Genevieve Winery at Fort Stockton marketed a special vintage called “Earthquake Red” ($4.99 a bottle). Its label was similar to the usual Ste. Genevieve label but featured a visible fault line. Photo by Tom Frohlich. Used with permission.

Austin American-Statesman, 14 April 1995: “Quake Rattles Texas; Temblor Felt in Austin / Starts Small Fires and Cracks Plaster in West Texas” Baltimore Sun, 15 April 1995: “Quake Sets off Burglar Alarms in Texas Town Near Epicenter” Memphis (Tenn.) Commercial Appeal, 15 April 1995: “West Texas Trembles During 5.6 Temblor” Dallas Morning News, 15 April 1995: “Texans Swap Tales of Quake” Dallas Morning News, 15 April 1995: “All Shook Up / Seismic Fluke Gives a Workout to Devices SMU Designed to Monitor Nuclear Blasts” 226

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Dallas Morning News, 15 April 1995: “Temblor Is Talk of the Town in Alpine” Dallas Morning News, 17 April 1995: “Governor Considers Quake Aid” Dallas Morning News, 18 April 1995: “Alpine Unlikely to get Disaster Funds, Ofﬁcial Says” Dallas Morning News, 19 April 1995: “For an Earth-Shaking Experience, Vacation in Texas” Dallas Morning News, 13 November 1995: “Aftershock of April Quake Hits Southeast of El Paso” El Paso Herald-Post, 14 April 1995: “Earthquake Shakes Up West Texas” Houston Chronicle, 15 April 1995: “West Texas Quake Doesn’t Mean Bigger Ones on the Way” Los Angeles Times, 14 April 1995: “5.6 Quake Jolts Texas, New Mexico” Midland Reporter Telegram, 15 April 1995: “Quake Causes Minor Damage Near Epicenter” Midland Reporter Telegram, 15 April 1995: “Temblor Jolts West Texas” New Orleans Times-Picayune, 15 April 1995: “Unusual Quake Hits Texas; State Isn’t Known for Tremors” Pecos Enterprise Online, 15 April 1995: “Geologists Cite Del Norte Fault as Probable Quake Cause” Pecos Enterprise Online, 18 April 1995: “Pipeline Blast Might Have Link to Quake” Pecos Enterprise Online, 13 November 1995: “Aftershock Hits Alpine Area” Pecos Enterprise Online, 9 October 1997: “Cracks Stir Up Verhalen Man’s Curiosity” Pecos Enterprise Online, 15 April 1998: “West Texas Rocks, Rolls Again” Pecos Enterprise Online: “Adobe Houses on Quake Worry List” Pecos Enterprise Online: “Pre-Easter Rumble Shocks All West Texas” Pecos Enterprise Online: “Project Near Sierra Blanca Would Withstand Tremor” San Angelo Standard Times, 14 April 1995: “Angelo Felt Tremor, Too” San Angelo Standard Times, 14 April 1995: “Big Bend Shakes” San Angelo Standard Times, 15 April 1995: “After the Shock Wears Off” San Jose Mercury News, 14 April 1995: “Even Earthquakes are Big in Texas / Stunned Residents Weather Strongest Temblor in 60 Years” Santa Fe New Mexican, 15 April 1995: “No Damage From Quake” A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

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St. Petersburg Times, 29 October 1989: “Alpine Texas / Earthquakes? Not Here. Tornadoes? Hurricanes? Never Heard of ‘Em. If You’re Serious About Avoiding Natural Disaster, This Southwest Town is Home Sweet Home” UPI, 14 April 1995: “West Texans Assess Quake Damage”

Alpine Region—14 April to 12 November 1995 (Various aftershocks) The National Earthquake Information Service located ten aftershocks in the twenty-four hours following the main shock; many of these were felt. The San Angelo Standard Times reported an interview with one rancher near the epicenter: [She] estimated the initial quake lasted about ﬁve seconds, followed by shorter aftershocks. “We’ve had about seven aftershocks, and one of them was pretty big but didn’t last long,” she said. “More than anything, you could hear them roar, coming down the canyon.”

The Dallas Morning News likewise reported that “some Alpine residents said they believed they felt aftershocks early Friday.” The largest aftershock occurred at 14:33 UTC (9:33 a.m. CDT) on 15 April, with moderate intensities felt over an area of approximately 52,000 km2. The National Earthquake Information Service reported intensities of MMI VI and slight damage at Alpine. According to the Dallas Morning News, there were “no reported injuries, although a few homeowners said the aftershock worsened some of the damage” and that “the aftershock prompted Alpine ofﬁcials to say cumulative damage is worse than initially thought.” Aftershocks continued throughout the year (see table 9.2). The National Earthquake Information Service reported that the shock on 1 June with mbLg of 3.5 was felt in Alpine, McCamey, and Big Bend National Park, suggesting a felt area of about 36,000 km2. Another event with mbLg of 3.6 also occurred on 12 November. While these events received brief mention in papers such as the Dallas Morning News and the Pecos Enterprise, we have no additional information about felt effects.

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Figure 9.27. Felt area map for the 15 April 1995 Alpine aftershock. Solid line indicates approximate extent of felt area. Dashed lines indicate county boundaries; labeled towns indicate where news reports indicated that citizens felt the 14 April 1995 main shock.

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Table 9.2 / AFTERSHOCKS OF 14 APRIL 1995 EARTHQUAKE IN ALPINE, TEXAS, as reported by the International Seismological Centre (ISC) or the National Earthquake Information Service (NEIS) DATE AND TIME

LATITUDE

N

LONGITUDE

W

NUMBER STATIONS m bLg

AGENCY

COMMENTS

14 April 1995 01:11:48.4

2.7

NEIS

14 April 1995 02:14:26.0

2.8

NEIS

3.3

ISC

Felt

14 April 1995 03:48:42.0

2.6

NEIS

Felt

14 April 1995 04:11:16.0

2.4

NEIS

Felt

14 April 1995 05:53:39.0

2.7

NEIS

14 April 1995 07:39:36.5

2.4

NEIS

Felt

14 April 1995 08:27:12.5

2.8

NEIS

Felt

2.9

ISC

Felt

14 April 1995 10:57:20.4

2.3

NEIS

Felt

15 April 1995 03:18:05.0

2.4

NEIS

Felt

14 April 1995 02:19:40

14 April 1995 10:02:58

30.5

30.3

103.1

103.3

7

4

(continued) Headlines

Associated Press, 13 November 1995: “Aftershock Hits Alpine Area” Atlanta Journal, 16 April 1997: “Aftershock” Dallas Morning News, 1 June 1997: “Weak Tremor Delivers ‘a Quick Jolt’ to Alpine Area; No Damage Reported” Dallas Morning News, 13 November 1995: “Aftershock of April Quake Hits Southeast of El Paso” Dallas Morning News, 15 April 1997: “Temblor is Talk of the Town in Alpine” Dallas Morning News, 15 April 1997: “Texans Swap Tales of Quake”

230

T E X A S E A RT H Q UA K E S

Table 9.2 / (continued) LATITUDE

N

LONGITUDE

W

NUMBER STATIONS m bLg

AGENCY

COMMENTS

30.26

103.33

15

4.0

ISC

Felt. Slight damage, MMI VI at Alpine; mb 3.2 (see text)

16 April 1995 00:40:43.3

2.3

NEIS

16 April 1995 10:26:25.5

2.5

NEIS

16 April 1995 16:16:09.6

2.4

NEIS

17 April 1995 08:50:00.5

2.5

NEIS

21 April 1995 04:41:44.0

2.9

NEIS

Felt, MMI III at Alpine

1 June 1995 01:06:15.7

3.5

NEIS

Felt, MMI IV at Alpine. Also felt at McCamey and Big Bend National Park

6 July 1995 02:41:51.0

2.7

NEIS

Felt at Alpine

6 July 1995 02:47:04.0

2.6

NEIS

Felt at Alpine

3.6

ISC

Felt at Alpine

DATE AND TIME

15 April 1995 14:33:29.7

12 Nov. 1995 17:45:60

30.2

103.2

8

Dallas Morning News, 16 April 1995: “New Aftershock Gives Alpine Another Shiver” Dallas Morning News, 17 April 1997: “Governor Considers Quake Aid / Aftershocks Prompt Damage Review Today” Dallas Morning News, 18 April 1997: “Alpine Unlikely to get Disaster Funds, Ofﬁcial Says” Pecos Enterprise Online: “Aftershock Hits Alpine Area” Pecos Enterprise Online: “Aftershocks Continue to Shake Alpine Area”

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

231

SOUTH OF MCLEAN — 23 NOVEMBER 1996 TO 5 MARCH 1997 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned: Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

23:53:11 UTC (12 Feb. 1997) 35.11 N 100.60 W IV 110km2 mbLg 3.0

(This study) (This study) (This study) National Earthquake Information Service

09:08:55 UTC (15 Feb. 1997) 35.11 N 100.60 W V 110km2 mbLg 3.2

(This study) (This study) (This study) National Earthquake Information Service

Pecos Enterprise Online: “West Texas Rocks, Rolls Again” San Angelo Standard Times, 15 April 1995: “Ranch at Epicenter Heard Quake’s Roar” Minneapolis Star Tribune, 16 April 1995: “West Texas Rattled by Quake Aftershock”

Coleman—15 December 1995 (Probable spurious earthquake report) An article in the Dallas Morning News reported a small earthquake in Coleman, Texas. The article in its entirety reads: COLEMAN, Texas—At least one small earthquake rattled this West Texas town Friday, but no damage or injuries were reported. The 3.1-magnitude temblor struck at 3:33 a.m. near Coleman, south of Abilene and 165 miles west of Dallas. Some residents of Coleman also said they felt the ground shake late Friday morning, but ofﬁcials of the U.S. Geological Survey’s National Earthquake Information Center in Golden, Colo., said they could not conﬁrm another temblor.

We could not locate the original source of this information, as the event does not appear in the listings of the National Earthquake Information Service. In addition, it wasn’t located by the Oklahoma Geological Observatory, nor did an examination of records from station HKT in Texas reveal any event at this time. Headline

Dallas Morning News, 16 December 1995: “Earthquake Shakes West Texas Town”

South of McLean—23 November 1996 to 5 March 1997 A few small earthquakes with mbLg of about 3.2 occurred in the eastern Texas Panhandle during late 1996 and early 1997. In early March 1997 the University of Texas Institute for Geophysics received a phone call from a Zelda McClellan,

232

T E X A S E A RT H Q UA K E S

ALICE — 24 MARCH 1997 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

22:31:34 UTC 27.70 N 97.95 W V–VI 950km2 mbLg 3.8

Bilich and others (1998) Bilich and others (1998) (This study) National Earthquake Information Service

who lived south of McLean, Texas, stating that she and her neighbors had felt an earthquake on 12 February 1997 at approximately 6 p.m. local time. Another shock on 15 February shook dishes and awakened sleepers in one household; one family thought a plane had crashed near their house. The National Earthquake Information Service located small earthquakes in the area that occurred at these times, and these are undoubtedly what McClellan and her neighbors experienced. McClellan also stated that she and her neighbors had felt four earthquakes altogether during the few months prior to 4 March 1997, culminating in a small shock on that day at 7:45 p.m. CST (1:45 UTC on 5 March). Moreover, she stated that these shocks were apparently not felt 10 km north in the town of McLean. While the National Earthquake Information Service did report an earthquake with mbLG of 3.0 in this region on 23 November 1996, neither they nor the Oklahoma Geological Observatory located any earthquakes in that area on 4 March 1997. However, it seems likely that a small, shallow earthquake did occur that was felt but not located. Alice—24 March 1997 This highly unusual small earthquake occurred on the southern Gulf Coast of Texas near the town of Alice, about 75 km west of Corpus Christi. Students at the University of Texas at Austin undertook a felt-report survey (Bilich and others 1998) using phone interviews, personal interviews, and a questionnaire published in the Alice Echo-News. The highest intensities of V–VI occurred in a small region with an area of approximately 25 km2 centered about 10 –15 km southeast of Alice. Here the shaking caused alarm and very minor damage: The walls seemed to breathe in and out . . . The TV in the bedroom was ripped out of the wall, all the pictures moved, and some Easter eggs in a cabinet broke. The movement lasted about 30 seconds, and ended with a loud noise or clap. I was sitting at the kitchen table with my older children. At ﬁrst I thought the 5-yearold had gotten onto the tractor and run it into the house because there was a big boom when it hit. A small crack in the barn ﬂoor opened to a 2 inch width. My husband observed the truck parked in ﬁrst gear moved about 18 inches.

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

233

Figure 9.28. Felt area map for the 24 March 1997 Alice earthquake. Roman numerals denote Modified Mercalli Intensities; dashed lines indicate county boundaries. Shaded regions indicate major oil (dark shading) or gas (light shading) fields as mapped by Galloway and others (1983) and Kosters and others (1989) that were established prior to 1989. Map and isoseismals are revised using information reported by Bilich and others (1998).

Although the Corpus Christi Caller Times stated that the National Earthquake Information Service “had received several calls from Corpus Christi residents saying they felt the tremor.” Bilich and others (1998) were unable to verify any felt reports from Corpus Christi. They concluded the report resulted from a misunderstanding between National Earthquake Information Service personnel and the author of the Caller Times article. Recently, Pulliam and Frohlich (2002) investigated the focal depth of this earthquake by comparing observed and synthetic short-period P-wave observa-

234

T E X A S E A RT H Q UA K E S

COMMERCE — 31 MAY 1997 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

03:26:41 UTC 33.18 N 95.97 W IV 1,100km2 mbLg 3.4; 3.5 mDUR 2.9

National Earthquake Information Service (This study) (This study) National Earthquake Information Service; TUL— Tulsa OK station TUL

tions for records at seismic stations HKT in Texas and WMOK in Oklahoma. They concluded that the focus was shallow, estimating a focal depth of 5 km. Commerce—31 May 1997 This small earthquake occurred in Hunt County in northeast Texas and was felt by residents of several small towns, including Commerce, Greenville, Celeste, Campbell, and Kingston (for a felt area map, see ﬁgure 9.12 with discussion of 12 April 1934 earthquake). According to the Greenville Herald Banner, in Kingston the shock was strong enough to elicit general alarm: More than 100 phone calls to the Hunt County Sheriff’s ofﬁce were reported from people in Kingston . . . The calls were reporting a loud noise or explosion in the area.

In Greenville the shock rattled a trailer and frightened at least one resident a little. There are conﬂicting reports as to the intensity at the town of Commerce itself. News items in the Austin American-Statesman and the Dallas Morning News suggested that the shaking caused a three-foot vertical crack observed in the wall of a campus building at Texas A & M University at Commerce. However, according to the Greenville Herald Banner the shock was not widely noticed: Commerce authorities said they received only one phone call, that from a lady in South Sulphur.

The National Earthquake Information Service reported that the shock was felt with MMI IV in Caddo Mills and MMI III in Canton. Canton is a considerable distance from the other felt locations, and we have been unable to learn the nature of the felt reports in either Canton or Caddo Mills. Pulliam and Frohlich (2002) investigated the focal depth of this earthquake by comparing observed and synthetic short-period P-wave observations for records at seismic stations HKT in Texas and WMOK in Oklahoma. They obtained a focal depth of 7.5 km. There have been at least two previous reports of small, unfelt events in the Commerce area. Davis, Pennington, and Carlson (1989) noted that the Okla-

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

235

ALPINE — 15 APRIL 1998 Origin time: Location: Maximum intensity: Felt area: Magnitudes assigned:

10:33:43 UTC 30.19 N 103.30 W III 3,900km2 mbLg 3.6

National Earthquake Information Service (This study) (This study) National Earthquake Information Service

homa Geological Observatory located a small event near Commerce on 23 March 1971 using phases from two regional stations; the location was not well constrained. Also, Sansom and Shurbet (1983) mention a local event recorded at a temporary seismic station at Commerce sometime between 1973 and 1980; they give no precise date and suggest the earthquake actually occurred in Oklahoma. Headlines

Austin American-Statesman, 1 June 1997: “Small Temblor Shakes Commerce” Caller-Times Interactive, 1 June 1997: “No Injuries In Light of Friday Night Tremor Near Commerce” Dallas Morning News, 1 June 1997: “Mild Quake Rattles Commerce Area” Greenville Herald Banner, 1 June 1997: “Minor Earthquake Shakes County”

Alpine—15 April 1998 Almost exactly three years after the 14 April 1995 Alpine earthquake, a mbLg 3.6 aftershock struck the same general area. Residents of Alpine and Marathon felt the tremor, as did a few people in neighboring Presidio County. According to the Pecos Enterprise, the departmental secretary of the Geology Department at Sul Ross State University at Alpine “did receive one call from a woman near Marathon complaining about the movement. ‘I told her it may be time to start thinking about moving.’” The San Angelo Standard Times reported that “vibrations of Wednesday’s quake could be felt in Alpine and westward to Calamity Creek; however, communities east of Marathon and south to Big Bend did not report any activity.” The paper also quoted a local rancher: “It shook the house and made the dogs bark.” The Blanca Nuclear Waste News noted that the shock generated some interest among opponents of a proposed low-level waste facility near Sierra Blanca. None of our sources reported any damage from the shock. Headlines

El Paso Times, 16 April 1998: “Small Earthquake Jolts Panhandle Area” Midland Reporter Telegram, 16 April 1998: “Aftershock from ‘95 Quake Rocks Alpine Residents” Nuclear Waste News, 7 May 1998: “Slants and Trends” Pecos Enterprise, 15 April 1998: “West Texas Rocks, Rolls Again” San Angelo Standard Times, 16 April 1998: “Earthquake Shakes Marathon” 236

T E X A S E A RT H Q UA K E S

LAWTON, OKLAHOMA — 28 APRIL 1998 Origin time: Location: Maximum intensity: Magnitudes assigned:

14:13:02 UTC 34.78 N 98.42 W VI mbLg 4.2

National Earthquake Information Service National Earthquake Information Service National Earthquake Information Service; TUL— Tulsa OK station

Lawton, Oklahoma—28 April 1998 This earthquake in southwestern Oklahoma near Lawton produced minor damage in Oklahoma’s Comanche County. The Oklahoma Geological Survey reported that the magnitude of 4.2 made it the eighth largest earthquake in Oklahoma history. The epicenter of the shock was close to the southeast end of the Meers Fault (see ﬁgure 2.6). Both the Daily Oklahoman and the Associated Press reported that the shock produced a great deal of commotion at the historic Meers Store and Restaurant. The shock was felt in Texas. The Fort Worth Star-Telegram of 29 April 1998 mentioned that the tremor was felt in Wichita Falls. Several sources list a single felt report in the Carrollton-Dallas area, variously given as “an individual in a high-rise in Dallas” by the Amarillo Daily News, a report from Carrollton, Texas, mentioned in the Daily Oklahoman, and a “three-story apartment building near Dallas, Texas” (Jim Lawson, personal communication). The Associated Press reported that people in Childress, Texas, did not feel the quake. Headlines

Amarillo Daily News, 29 April 1998: “Earthquake Rattles Southern Oklahoma, but not Childress” Associated Press, 29 April 1998: “Earthquake Rattles Southern, Central Oklahoma” Daily Oklahoman, 29 April 1998: “Dateline: Meers”

Amarillo—2 August to 17 August 2000 Some residents of north Amarillo felt all six of these earthquakes; the two largest, which occurred on 7 August and 17 August, also were felt in some neighboring communities. In north Amarillo the 17 August event produced hairline cracks in a few walls, caused old underground pipes and some gas lines to crack, made hanging pictures swing out of place, and caused a few people to run outdoors. Intensities reached MM IV in Canyon to the south of Amarillo and MM III in Valle de Oro to the northeast. Strangely, the Amarillo Globe-News initially quoted a National Earthquake Information Center report stating that it was felt in White Deer, 60 km to the west of Amarillo. However, this was not conﬁrmed by a more thorough subsequent NEIC report, and thus our felt-area estimate of 5000 km2 presumes that the felt area does not extend eastward as far as Panhandle or Claude. The 17 August earthquake is the ﬁrst signiﬁcant Texas A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

237

AMARILLO — 2 AUGUST TO 17 AUGUST 2000 Origin time (Largest Event): Location: Maximum intensity: Felt Area: Magnitudes assigned:

17 August 01:08:05 UTC 35.38 N 101.84 W V 5,000km2 mbLg 3.9

Origin times (Foreshocks):

2 August 12:21:30 UTC (b) 7 August 17:19:06.6 (c) 7 August 18:34:07.9 (d) 7 August 21:36:21 (e) 10 August 13:39:50 35.2 N 101.9 W (b) 35.37 N 101.87 W (c) 35.36 N 101.91 W (d) 35.33 N 101.89 W (e) 35.20 N 101.9 W III (b) III (c) Felt (d) Felt (e) Felt mbLg 2.7 (b) mbLg 3.3 (c) mbLg 3.0 (d) mbLg 3.0 (e) mbLg 3.0

Locations:

Maximum intensities:

Magnitudes assigned:

National Earthquake Information Center National Earthquake Information Center (This study) National Earthquake Information Center

National Earthquake Information Center

National Earthquake Information Center

National Earthquake Information Center

earthquake to occur since the U.S. Geological Survey began collecting felt reports over the Internet to produce Community Internet Intensity Maps (see chapter 1, note 2); as of 30 August 2000 the USGS had received felt reports indicating intensities of MM III or greater for this earthquake from ninety citizens in eighteen zip codes. The felt reports suggest that the 7 August and 17 August quakes may have had different epicenters. In particular, for 7 August there were MM III felt reports from Panhandle and Tulia, cities east of Amarillo that did not report the 17 August quake. The 7 August event was felt distinctly in north Amarillo. As one resident told an Amarillo Globe-News reporter, “It sounded like two dump trucks colliding, or an explosion. There was the sound, then a momentary shake that shook the house a little. It was kind of like your mama caught you by the shoulders and gave you a shake to get you right.”

238

T E X A S E A RT H Q UA K E S

AMARILLO — 16 DECEMBER 2000 Origin time Location: Maximum intensity: Magnitude assigned:

16 December 22:08:54 UTC 35.39 N 101.81 W ? mbLg 3.9

National Earthquake Information Center National Earthquake Information Center National Earthquake Information Center

Headlines

Amarillo Globe-News, 3 August 2000: “Quake Shakes North Amarillo” Amarillo Globe-News, 8 August 2000: “Three Minor Earthquakes Shake Amarillo Area” Amarillo Globe-News, 10 August 2000: “Another Tremor Reported” Amarillo Globe-News, 17 August 2000: “Strongest of Six Earthquakes Hits Amarillo”

Amarillo—16 December 2000 The National Earthquake Information Center located this earthquake on the basis of arrivals at six stations in Texas, Oklahoma, Colorado, Arkansas, and Kansas and noted that it was “felt in the Amarillo area.” Its assigned magnitude of 3.9 is the same as for the 17 August 2000 Amarillo quakes. However, it seems to have generated very little excitement; the Amarillo Globe-News story stated only that it “shook through Amarillo Saturday afternoon, according to information from the National Earthquake Information Center.” The U.S. Geological Survey did collect felt reports over the Internet for the 16 December earthquake to produce a Community Internet Intensity Map, but it received only four reports from three zip codes indicating intensities of MMI III or greater. This suggests that the 16 December earthquake is somewhat smaller than the 17 August 2000 Amarillo event, for which USGS received ninety Internet reports indicating MMI III or greater. Headlines

Amarillo Globe-News, 17 December 2000: “Quake Recorded” Austin American-Statesman, 18 December 2000: “7th Quake of Year Rattles Amarillo”

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

239

Table 9.3 / TEXAS EARTHQUAKES OF MAGNITUDE 3 OR MORE *MAGNITUDE TYPES ARE AS FOLLOWS:

a magnitude derived from felt effects b ML (local magnitude) c mb (body wave magnitude) d “corrected” magnitude (Rogers and Malkiel 1979) 240

e coda length f mbLg (magnitude derived from 1-second Lg waves)

T E X A S E A RT H Q UA K E S

g MS (surface wave magnitude) **Imax Maximum Modified Mercalli Intensity reported ***CAUSE:

T probably tectonic in origin M probably man-made (induced) U origin uncertain ? Insufficient or conflicting evidence available, possibly an earthquake but may be spurious

DATE

ORIGIN TIME (UTC)

LAT.

N

14 Feb. 1847

02

29.6

LONG.

W

98.0

MAGNITUDE

FELT

AND TYPE*

IMAX**

AREA (KM 2 )

CAUSE***

LOCATION

3.6a

V

1,200

T

Seguin

Comments: Newspaper reports cracked timber in houses at Seguin and New Braunfels. (continued)

Table 9.3 / (continued) A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

DATE

ORIGIN TIME (UTC)

LAT.

N

1 May 1873

04:30

30.25

5 Jan. 1887

17:57

31 Jan. 1887 31 May 1889

LONG.

W

MAGNITUDE

FELT

AND TYPE*

IMAX**

AREA (KM 2 )

CAUSE***

LOCATION

97.6

3.1a

III–IV

—

?

Manor

30.15

97.06

4.1a

V–VI

4,600

T

Paige

22:14

30.53

96.3

3.3a

IV

—

?

Wellborn

20

32

106.5

3.6a

V

—

T

El Paso

Comments: Newspaper reports one building badly cracked by the shock. 8 Jan. 1891

06

31.7

95.2

4.0a

VI

—

T

Rusk

97.6

3.9a

IV–V

5,600

T

Creedmoor

Comments: Several chimneys thrown to the ground. 9 Oct. 1902

19

30.10

Comments: Newspapers report a window broken from the shock. 8 May 1910

17.30

30.1

96.0

3.8a

IV

2,900

T

Hempstead

30 Dec. 1914

01

30.5

95.9

3.3a

IV

—

?

Anderson

28 March 1917

19:56

35.4

101.3

3.9a

VI

7,600

U

Panhandle

31.8

106.5

4.7a

VI

200,000

T

El Paso

Comments: Reports of cracked plaster. 7 March 1923

05:03

241

Comments: Collapse of an adobe house killed a man in Juarez, Mexico, a few miles from the Texas border. Windows broke in El Paso. Epicenter may have been in Mexico. (continued)

Table 9.3 / (continued) DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

AND TYPE*

IMAX**

AREA (KM 2 )

CAUSE***

LOCATION

29 July 1925

11:30

34.5

101.2

3.3a

IV

—

?

Silverton

30 July 1925

12:17

35.4

101.3

5.4a

VI

520,000

U

Panhandle

MAGNITUDE

FELT

Comments: A large cistern cracked, and a coal bin broke. A railroad track needed repairs after the shock. Other reports of damage include cracked plaster and a fallen chimney. 242 T E X A S E A RT H Q UA K E S

31 July 1925

18

35.5

101.1

3.0a

III

—

?

White Deer

16 Aug. 1931

08

30.7

104.6

3.6a

V

—

T

Valentine

16 Aug. 1931

11:15

30.7

104.6

3.0a

III

—

T

Valentine

16 Aug. 1931

11:40:22

30.7

104.6

6.0a

VIII

1,000,000

T

Valentine

Comments: Moderate to severe damage to buildings reported over several thousand square kilometers. Chimneys were knocked down, and cement and brick walls were cracked. Minor injuries from collapse of adobe structures reported. Landslides were reported in the epicentral regions. 16 Aug. 1931

12:17

30.7

104.6

3.0a

III

—

T

Valentine

16 Aug. 1931

12:45

30.7

104.6

3.3a

IV

—

T

Valentine

16 Aug. 1931

13:35

20.7

104.6

3.3a

IV

—

T

Valentine

16 Aug. 1931

19:33

30.7

104.6

3.6a

V

—

T

Valentine (continued)

Table 9.3 / (continued)

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

AND TYPE*

IMAX**

AREA (KM 2 )

CAUSE***

LOCATION

18 Aug. 1931

08:42

30.7

104.6

3.0a

III

—

T

Valentine

18 Aug. 1931

19:36

30.7

104.6

4.2a

V

20,000

T

Valentine

MAGNITUDE

FELT

Comments: Newspapers report the collapse of several adobe structures that had been damaged by the 16 August earthquake. Walls cracked and plaster fell. 18 Aug. 1931

22

30.7

104.6

3.0a

III

—

T

Valentine

26 Aug. 1931

—

30.7

104.6

3.6a

III

6,800

T

Valentine

2 Oct. 1931

—

31.8

106.5

3.2a

II–III

—

T

El Paso

3 Nov. 1931

15:50

30.7

104.6

3.0a

III

—

T

Valentine

9 April 1932

10:17

31.7

96.4

4.0a

VI

6,400

M

Wortham-Mexia

Comments: In Wortham, bricks from several chimneys were shaken loose. The mortar of one building was cracked. 12 April 1934

01:40

33.9

95.5

4.2a

V

13,000

T

Trout Switch

Comments: One house needed releveling after the shock.

243

19 June 1936

21

35.2

100.7

3.0a

III

—

?

Clarendon

20 June 1936

03:13:37

35.7

101.4

3.9a

III

—

U

Borger

20 June 1936

03:18:27

35.7

101.4

3.9a

III–IV

21,000

U

Borger

20 June 1936

03:24:06

35.7

101.4

5.0a

VI

110,000

U

Borger

Comments: At Pampa, dishes were broken and small cracks in buildings were noted. Buildings were also reported as cracked in Kenton, Oklahoma, and Elkhart, Kansas. (continued)

Table 9.3 / (continued) DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

AND TYPE*

IMAX**

AREA (KM 2 )

CAUSE***

LOCATION

8 Aug. 1936

01:40

31.8

106.5

3.0a

III

—

T

El Paso

15 Oct. 1936

18

31.8

106.5

3.0a

III

—

T

El Paso

31 March 1937

23:45

31.8

106.5

3.0a

III

—

T

El Paso1

12 March 1948

04:29

36.0

102.5

5.2a

VI

240,000

T

Dalhart

MAGNITUDE

FELT

244

Comments: Slight cracks in plaster reported in several cities.

T E X A S E A RT H Q UA K E S

20 Mar. 1950

13:23

33.3

97.8

3.3a

IV

—

?

Chico

20 June 1951

18:37:10

35.0

102.0

4.2a

V

74,000

U

Amarillo

Comments: Damage to plaster reported in Amarillo and Hereford. 17 Oct. 1952

15:48

30.1

93.8

3.3a

IV

—

?

Orange

27 Jan. 1955

00:37

30.6

104.5

3.3a

IV

—

T

Valentine

19 Mar. 1957

16:37:39

32.6

94.7

4.7a

V

45,000

M

Gladewater

19 Mar. 1957

17:41:17

32.6

94.7

3.0a

III

3,000

M

Gladewater

19 Mar. 1957

22:36

32.6

94.7

3.0a

III

3,000

M

Gladewater

19 Mar. 1957

22:45

32.6

94.7

3.0a

III

3,000

M

Gladewater

6 Mar. 1962

09:59:10

31.2

104.8

3.5b

—

—

T

Van Horn area

24 April 1964

01:20:55

31.5

93.9

3.7c

V

—

T

Hemphill (continued)

Table 9.3 / (continued)

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

DATE

ORIGIN TIME (UTC)

LAT.

N

24 April 1964

07:33:53

31.6

24 April 1964

12:07:07

27 April 1964 28 April 1964

LONG.

W

MAGNITUDE

FELT

AND TYPE*

IMAX**

AREA (KM 2 )

CAUSE***

LOCATION

93.9

3.7c

IV

—

T

Hemphill

31.3

93.8

3.2c

IV

—

T

Hemphill

21:50:27

31.3

93.8

3.2c

IV

—

T

Hemphill

21:18:35

31.3

93.8

4.4c

VI

2,700

T

Hemphill

Comments: A small fissure opened up in the yard of a Plainview resident on 27 April. Wallpaper and plaster cracked during the April 23 shock.

245

30 April 1964

20:30:00

31.5

93.8

3.0c

III

—

T

Hemphill

7 May 1964

07:33:53

31.2

94.0

3.2c

V

—

T

Hemphill

2 June 1964

23:00:00

31.3

94.0

4.2c

V

—

T

Hemphill

3 June 1964

00:00:00

31.3

94.0

4.2c

V

—

T

Hemphill

3 June 1964

02:27:24

31.5

93.9

3.1c

III

—

T

Hemphill

3 June 1964

09:37:00

31.0

94.0

3.6c

IV

—

T

Hemphill

8 Nov. 1964

09:25:59

31.9

103.1

3.0d

—

—

U

Kermit

21 Nov. 1964

11:21:22

31.9

103.1

3.1d

—

—

U

Kermit

3 Feb. 1965

19:59:32

31.9

103.1

3.3d

—

—

U

Kermit

30 Aug. 1965

05:17:30

31.9

103.0

3.5c

—

—

U

Kermit

20 July 1966

09:04:58

35.7

101.2

4.1a

V

36,000

U

Borger

14 Aug. 1966

15:25:47

31.9

103.0

3.4c

VI

50,000

U

Kermit

Comments: Street signs were knocked down and windows broken at Kermit. (continued)

Table 9.3 / (continued) DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

AND TYPE*

IMAX**

AREA (KM 2 )

CAUSE***

LOCATION

12 May 1969

08:26:19

31.8

106.4

3.9b

VI

—

T

El Paso

12 May 1969

08:49:16

31.8

106.4

3.6b

VI

—

T

El Paso

MAGNITUDE

FELT

Comments: Cracks in a ceiling and on a driveway were reported at El Paso.

246 T E X A S E A RT H Q UA K E S

30 July 1971

01:45:51

31.72

103.00

3.0c

—

—

U

Kermit

31 July 1971

14:53:49

31.70

103.06

3.4c

—

—

U

Kermit

24 Sept. 1971

01:01:54

31.6

103.2

3.2d

—

—

U

Kermit

9 Dec. 1972

05:58:44

31.75

106.40

3.0b

IV

1,500

T

El Paso

10 Dec. 1972

14:37:50

31.75

106.40

3.0b

III

100

T

El Paso

25 Dec. 1973

02:46:10

28.82

98.20

3.2e

IV

—

M

Fashing

15 Feb. 1974

13:33:50

36.39

100.52

4.5c

V

110,000

T

Perryton

Comments: Glasses broke and walls cracked at Perryton. Cracks in walls or plaster were also reported in six other cities in Texas, Oklahoma, and Kansas. 20 April 1974

23:46:10

29

98

3.0e

—

—

M

South Texas

24 June 1974

18:03:10

29

98

3.4e

—

—

M

South Texas

1 Aug. 1974

13:33:10

29

98

3.0e

—

—

M

South Texas

30 Dec. 1974

08:05:27

30.9

103.1

3.7b

—

—

T

Fort Stockton

1 Aug. 1975

07:27:57

31.4

104.0

3.0f

II

—

T

Del. Basin (continued)

Table 9.3 / (continued)

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

AND TYPE*

IMAX**

AREA (KM 2 )

CAUSE***

LOCATION

19 Jan. 1976

04:03:30

31.90

103.09

3.5b

IV

—

U

Kermit

25 Jan. 1976

04:48:28

31.90

103.09

3.9b

V

2,000

U

Kermit

5 Aug. 1976

18:53:09

31.6

103.0

3.0b

—

—

U

Kermit

17 Sept. 1976

03:56:29

31.4

102.5

3.1d

—

—

U

Kermit

26 April 1977

09:03:07

31.9

103.1

3.3b

IV

—

U

Kermit

7 June 1977

23:01:20

33.0

100.7

3.1e

—

—

M

Snyder

22 July 1977

04:01:10

31.8

102.7

3.0d

—

—

U

Kermit

2 March 1978

10:04:53

31.55

102.56

3.5b

III

—

U

Kermit

16 June 1978

11:46:54

33.01

100.72

4.6f

V

100,000

M

Snyder

MAGNITUDE

FELT

Comments: Windows broke at Snyder, Fluvanna, and Peacock. Small objects broke at Carlsbad, New Mexico, and cracked plaster was reported at Justiceburg. 16 June 1978

11:53:33

33.0

100.8

3.4f

—

—

M

Snyder

9 June 1980

22:37:10

35.50

101.05

4.3a

V

35,000

U

Pampa

Comments: Reports of cracked plaster at Pampa.

247

9 June 1981

01:46:33

31.76

94.28

3.2f

III

—

T

Center

6 Nov. 1981

12:36:41

31.95

95.92

3.3f

V

800

T

Jacksonville

Comments: Reports of minor damage include cracks in concrete patios and windows and a broken water pipe. (continued)

Table 9.3 / (continued) DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

AND TYPE*

IMAX**

AREA (KM 2 )

CAUSE***

LOCATION

4 Jan. 1982

16:56:10

31.18

102.35

3.9f

III

2,500

T

Fort Stockton

28 March 1982

23:24:33

29

3.0e

—

—

M

South Texas

14 Oct. 1982

12:52:46

36.05

3.9f

III

8,200

T

Dalhart

98 102.53

MAGNITUDE

FELT

Comments: A crack in a parking lot was reported at Dalhart. 248 T E X A S E A RT H Q UA K E S

7 Nov. 1982

00:04:19

35.2

100.2

3.1f

—

—

U

Wheeler Co.

28 Nov. 1982

02:36:48

32.92

100.85

3.3f

IV

32,000

M

Snyder

23 July 1983

15:24:39

28.82

98.18

3.4f

V

200

M

Fashing

1,300

M

Pleasanton

Comments: A boiler at a gasoline plant was automatically shut down by the shaking. 3 March 1984

01:03:26

28.87

98.50

3.9f

V

Comments: A few possible reports of plaster cracking and cracks in concrete being widened by the shock. 3 March 1984

01:58:25

28.87

3 April 1984

04:55:24

35.32

21 May 1984

13:30:14

35.4

8 Aug. 1984

01:31:27

29.87

11 Sept. 1984

14:47:33

19 Sept. 1984 18 Sept. 1985

3.2e

IV

100

M

Pleasanton

102.4

3.4f

—

—

T

Oldham Co.

102.4

3.1f

—

—

T

Oldham Co.

98.50

3.1f

IV

—

M

Pleasanton

31.96

100.66

3.0f

—

—

U

Coke County

06:15:42

32.03

100.68

3.2f

—

—

U

Coke County

15:54:04

33.47

97.04

3.3f

V

700

T

Valley View

98.50

(continued)

Table 9.3 / (continued)

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

AND TYPE*

IMAX**

AREA (KM 2 )

CAUSE***

LOCATION

30 Jan. 1986

22:26:37

32.02

100.70

3.3f

IV

—

U

Silver

3 March 1986

11:45:17

35.31

102.52

3.1f

—

—

U

Oldham Co.

20 July 1991

23:38:17

29.0

98.0

3.6f

IV

110

M

Falls City

2 Jan. 1992

11:45:36

32.36

102.97

4.6c

V

440,000

T

Rattlesnake Canyon

4.3f

VI

5,000

M

Fashing

MAGNITUDE

FELT

Comments: Felt over a wide area but only minor damage reported. 9 April 1993

12:29:19

28.87

98.50

Comments: Ground motion triggered a shutdown of a gas plant. Damage at the plant included broken concrete blocks and stretched or broken bolts. Other minor damage reported in neighboring communities. 16 May 1993

15:30:19

28.9

98.5

3.0f

IV

300

M

Jourdanton

T

Alpine

Comments: A few possible reports of plaster cracking and cracks in concrete being widened by the shock. 14 April 1995

00:32:56

30.28

103.35

5.7g

VI

760,000

Comments: Reports of damaged water mains and a broken fire hydrant, cracked walls and windows, broken dishes, and dislodged suspended ceilings. Broken gas mains resulted in several small fires. Landslides reported, most notably from the peak of Cathedral Mountain.

249

14 April 1995

02:19:38

30.28

103.35

3.3f

felt

—

T

Alpine

15 April 1995

14:33:30

30.28

103.35

4.0f

VI

52,000

T

Alpine

Comments: Slight damage reported. (continued)

Table 9.3 / (continued)

250 T E X A S E A RT H Q UA K E S

DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

AND TYPE*

IMAX**

AREA (KM 2 )

CAUSE***

LOCATION

1 June 1995

01:06:16

30.28

103.35

3.5f

IV

36,000

T

Alpine

12 Nov. 1995

17:45:59

30.28

103.35

3.6f

felt

—

T

Alpine

25 March 1996

06:43:47

35.61

102.60

3.5f

—

—

T

near Channing

23 Nov. 1996

10:54:18

35.04

100.50

3.0f

possibly felt

—

U

near McLean

12 Feb. 1997

23:53:11

35.11

100.60

3.0f

IV

110

U

near McLean

15 Feb. 1997

09:08:55

35.11

100.60

3.2f

V

110

U

near McLean

24 March 1997

22:31:34

27.72

98.05

3.8f

V–VI

950

M

Alice

MAGNITUDE

FELT

Comments: Very slight damage reported, including broken Easter eggs. 31 May 1997

03:26:41

33.2

96.1

3.4f

IV

1,100

T

Commerce

3,900

T

Alpine

Comments: Slight damage reported. 15 April 1998

10:33:43

30.19

103.30

3.6f

III

7 Aug. 2000

17:19:07

35.20

101.90

3.3f

III

U

Amarillo

7 Aug. 2000

18:34:08

35.37

101.87

3.0f

III

U

Amarillo

7 Aug. 2000

21:36:21

35.36

101.91

3.0f

III

U

Amarillo

10 Aug. 2000

13:59:50

35.20

101.90

3.0f

III

U

Amarillo

17 Aug. 2000

01:08:05

35.38

101.84

3.9f

V

U

Amarillo

16 Dec. 2000

22:08:39

35.20

101.81

3.9f

IV

U

Amarillo

5,000

Table 9.4 / REGIONAL EARTHQUAKES FELT IN TEXAS DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

16 Dec. 1811

08:15

36.0

90.0

8.1

New Madrid MO

23 Jan. 1812

15:00

36.3

89.6

7.8

New Madrid MO

7 Feb. 1812

09:45

36.5

89.6

8.0

New Madrid MO

MAGNITUDE LOCATION

Comments: Probably felt in Texas, but no verifiable accounts known. The formation of Caddo Lake in northeast Texas has been attributed to these earthquakes, but accounts of the lake exist prior to 1811. 22 Oct. 1882

22:15

35.9

95.1

5.6

Ft. Gibson OK

Comments: Previously listed as occurring near Paris, Texas. Bricks were shaken loose from walls and chimneys at Bonham, Texas. 1 Sept. 1886

02:51

33

80

6.7

Charleston SC

Comments: Several water wells in the Forth Worth, Texas, area were muddied and charged with sulfur after the earthquake. 3 May 1887

22:13

30.8

109.1

7.4

Sonora, Mexico

Comments: Felt as far east as Fort Davis, Texas. Newspapers report that several buildings were badly cracked in El Paso, Texas. 31 Oct. 1895

11:08

37.0

89.4

6.2

New Madrid MO

Comments: Reported as felt in New Mexico. North Texas lies within the probable felt area, although there are no known reports from this region. — 1906

—

34.0

107.0

—

Socorro NM

Comments: Earthquakes on 12 July, 16 July, and 15 November felt in El Paso, Texas. 1 Nov. 1928

04:16

26

106

6.3

Mexico

Comments: Felt with intensity VI in El Paso and Valentine and with intensity IV in Pecos, Texas. 14 Mar. 1936

17:20

34.0

95.0

4.2

Valliant OK

Comments: Reported as felt in Manchester, Texas. (continued)

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

251

Table 9.4 / (continued) DATE

ORIGIN TIME (UTC)

LAT.

N

9 April 1952

16:29:34

35.4

LONG.

W

97.8

MAGNITUDE LOCATION

5.5

El Reno OK

Comments: Intensities III–V noted in much of north Texas. Felt as far south as Austin, Texas. 17 June 1959

16:27:07

34.5

98.5

4.7

Lawton OK

Comments: Felt in Wichita Falls, Gainesville, Nocona, and Dallas, Texas. 28 March 1964

03:36:14

61.0

147.5

8.5

Alaska

Comments: Large fluctuations in Texas water wells were noted; one Panhandle well was damaged and had to be abandoned. Minor damage to boats from waves in channels reports along the Texas and Louisiana coasts. Reports of water sloshing over the sides of swimming pools also came from this region. One felt report from a bridge tender in Louisiana. 12 Jan. 1970

11:21:15

36.1

103.2

4.2

Amistad NM

Comments: Felt in Texline, Texas. 16 April 1976

18:59:46

35.9

99.97

3.4

Durham OK

19 April 1976

04:42:44

35.9

99.97

3.5

Durham OK

8.1

Michoacan, Mexico

Comments: Both shocks felt with intensity IV in Higgins, Texas. 19 Sept. 1985

13:17:48

18.18

102.57

Comments: Felt in tall buildings in McAllen and in the Houston-Galveston area, Texas. Swimming pool seiches observed in many Texas cities. 30 Nov. 1993

03:07:32

35.86

103.03

3.3

Amistad NM

34.78

98.42

4.2

Lawton OK

Comments: Felt north of Sunray, Texas. 28 April 1998

14:13:02

Comments: Felt in Wichita Falls, Texas, as well as a report from the Dallas-Carrollton area.

252

T E X A S E A RT H Q UA K E S

Table 9.5 / UNUSUAL OR SPURIOUS REPORTS OF EARTHQUAKES DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

MAGNITUDE

LOCATION

1850s

—

30.3

97.8

—

Austin TX

Comments: Austin newspapers from 1902 mention an earthquake in the 1850s that caused the Colorado River to run backward and that killed large numbers of fish. No earlier report of this event has been found, and its authenticity is questionable. 3 Sept. 1886

10

32.8

97.4

—

Fort Worth TX

—

Port Lavaca TX

Comments: Possible report of a shock felt at Forth Worth, Texas. 8 May 1891

21:30

28.6

96.6

Comments: The New Orleans Picayune of 10 May 1891 reports that this shock “was accompanied by a peculiar noise or muffled detonation. . . . [It} caused people to run out of their houses and inquire what was the matter [and was] felt by boatmen on the bay.” 31 Aug. 1894

8

29.2

99.8

—

Uvalde TX

Comments: Major flooding in eastern and southern Texas caused widespread damage. At Uvalde a sudden flooding of the Leona River was attributed by some to an earthquake, but in all likelihood the storm and high river levels caused the observed effects. April 1907

00

11–12 May 1910

—

35.2 30.1

101.8

3.6a

Amarillo

96.0

3.8

Hempstead TX

Comments: Probably an account of the 8 May, 1910, Hempstead, Texas, earthquake with an erroneous date. 28 Jan. 1917

19:56

35.4

101.3

3.2

Panhandle

24 Mar. 1917

19:46

35.3

101.2

4.2

Panhandle

27 Mar. 1917

19:30

35.3

101.3

4.7

Panhandle

Comments: Probably accounts of the 28 March, 1917 Panhandle earthquake with erroneous dates. 27 Mar. 1917

23:38

35.3

101.3

—

Panhandle

28 Mar. 1917

23:38

35.3

101.3

—

Panhandle

Comments: No original account of this aftershock of the 1917 Panhandle earthquake has been found. (continued)

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

253

Table 9.5 / (continued) DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

MAGNITUDE

LOCATION

1925

—

29.5

94.8

—

Goose Creek TX

Comments: Several small shocks associated with subsidence. No exact dates given. 30 July 1925

06:11

—

—

—

Panhandle

Comments: Felt with intensities II-IV in Panhandle, Amarillo, Post, and Childress in Texas and Hobart in Oklahoma. May have been separate shocks. 6 Dec. 1925

16:21:24

30.0

97.0

—

La Grange TX

Comments: Spurious location based on seismic phases from earthquakes in California and Wyoming (see appendix C.4 in Davis, Pennington, and Carlson 1989). 18 –19 Oct. 1929

—

31.9

101.7

—

Big Spring area, TX

Comments: Early morning dynamite blasts for seismic exploration; originally thought to be a series of earthquakes. 31 Dec. 1934

18:46

32.0

114.8

7.0

Southern CA

Comments: Listed as felt with intensity I–III in El Paso, Texas. Probably a spurious report. 3 July 1935

—

—

—

—

E. of Padre Island TX

Comments: Fish killed and sulfide gas produced; originally thought by some to have been due to an earthquake. Investigations suggested that the phenomenon resulted from a flood of fresh water for the Nueces River. 8 Aug. 1937

01:40

—

—

—

El Paso TX

Comments: Listed in several catalogs, this is a spurious replication of the 8 August 1936 earthquake. 1942 –1948

—

30

103.5

—

Alpine TX

Comments: Possibly earthquakes felt at Alpine, Texas; no exact date given. 7 Jan. 1956

23:30

29.3

94.8

—

Galveston TX

36.2

95.8

4.7

Catoosa OK

Comments: Probably a sonic boom. 30 Oct. 1956

10:36:21

Comments: Listed as felt with intensity IV in Electra, Texas; probably a spurious report. (continued)

254

T E X A S E A RT H Q UA K E S

Table 9.5 / (continued) DATE

ORIGIN TIME (UTC)

LAT.

N

LONG.

W

MAGNITUDE

LOCATION

21 March 1957

—

29.5

95.5

—

Houston TX

Comments: Minor earth tremors reported by Houston residents about 9 P.M. local time on 20 March; probably strong winds or thunder. 10 Feb. 1959

20:05

—

—

—

Panhandle

Comments: Felt or heard in many Texas Panhandle and eastern New Mexico cities; probably sonic booms. Jan.–March 1966

—

30

94

—

Beaumont–Port Arthur area, TX

Comments: Several events felt on five separate days in southeast Texas and southwest Louisiana; probably sonic booms. June 1969

—

29.5

95.5

—

Houston TX

—

Travis Peak TX

Comments: Probably sonic booms on 12, 18, and 19 June. 3 Feb. 1970

—

30.52

98.05

Comments: Several events throughout the day; probably sonic booms or explosions. 1 Oct. 1971

18:49:39

35.8

90.4

4.1

Northeastern Arkansas

Comments: Listed as felt in Nacogdoches, Texas; possibly a spurious report. 14 Jan. 1977

14:05:13

32.2

99.5

—

Near Abilene TX

Comments: Erroneous location based on arrivals from a Mexican earthquake and a blast in a salt mine (see appendix C.5 in Davis, Pennington, and Carlson 1989). 3 Nov. 1986

—

—

—

—

Waco TX

Comments: Tremors probably resulting from bombing practice at nearby Fort Hood, TX. 15 Jan. 1987

11:30 –15:30

32.85

100.46

—

Rotan X

31.8

99.4

—

Coleman TX

Comments: Probably sonic booms. 15 Dec. 1995

9:33

Comments: Probably a spurious earthquake report.

A NEW COMPENDIUM OF EARTHQUAKE ACTIVITY IN TEXAS

255

Notes 1. For all practical purposes, UTC is the same as Greenwich Mean Time (GMT). However, in 1986 UTC became the world standard for time. UTC is based on very accurate atomic clocks, while GMT is based on measurements of the earth’s rotation. 2. See ﬁgure B6 in Davis, Pennington, and Carlson (1989). 3. See Davis, Pennington, and Carlson (1989) for a catalog of all available references to these foreshocks and aftershocks and a table summarizing reported origin times, maximum intensities, felt areas, and magnitudes. 4. Davis, Pennington, and Carlson (1989) present a felt area map for the ﬁrst two tremors and discuss the controversy surrounding the distribution of intensities. 5. The description suggests that this event could have been a sonic boom rather than an earthquake. However, we have been unable to determine if supersonic aircraft were in this region in 1950. 6. The peculiar long-period effects of the 1964 Alaska earthquake stimulated the imagination of crackpot scientists. For example, in 1966 a man named Burton C. Coons published a theory that dry steam from the interaction of ocean water and lava is the cause of all earthquakes, volcanoes, and tsunamis. Coons (1966) describes himself as a man “who has been for many years a very successful inventor and machine designer of complicated machinery; also, a successful business man, a deep thinker on all subjects, and born with a creative mind and writer of great vision.” He explains the 1964 Alaskan earthquake in terms of his theory as follows: [Seismologist L. J. Eisle of Spring Hill College, Alabama] stated there was no water connection between the West and the Gulf Coast. However, they did have the shaking of the earth and the tidal wave raised and lowered ﬁve feet in some places and eight feet in others [after the Great Alaskan Earthquake of 1964]. He did not say what caused this condition. I believe this situation is a clear proof of my statement in this book. Here is what happened: A Paciﬁc tidal wave was generated by the Alaskan earthquake. The tidal wave rolled the water at high speed toward the Hawaiian Islands, Japan and the West Coast of the Mainland. I would say that only a portion of this 10 million pounds of dry steam coming up through the hole or vent in the earth caused the Paciﬁc tidal wave, and the balance of dry steam, moving at lightning speed, followed other faults and cracks going in all directions. There appears to be a fault way down deep in the earth that runs between the Gulf of Mexico and Alaska because the only thing that would shake the earth and raise the water up and down 3,600 miles in distance would be the dry steam pressure from the Alaskan quake coming up closer to the earth’s surface near the Gulf, shaking the earth and ﬁnding an out way down deep in the bottom the Gulf, causing a small tidal wave. It is my opinion that a terriﬁc pressure of fast-moving dry steam would be the only power great enough to cause this condition. I want to discuss the question because many people have asked me “how can steam move 3,600 miles deep in the earth . . . without dissipating or disintegrating or losing its power?” My answer is: dry steam moves as fast as lightning. It would arrive down below the Gulf of Mexico from Alaska in two minutes . . . 7. For a reproduction see Davis, Pennington, and Carlson 1989. 256

T E X A S E A RT H Q UA K E S

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Index aftershocks Alpine, TX (1995), 228–232 Panhandle, TX (1925), 145 Pleasanton, TX (1984), 210 Valentine, TX (1931), 152–154, 256 Aki, Keiiti, 8 Amarillo-Wichita Uplift, 24, 28 Anadarko Basin, 24, 26, 29, 163, 172 Bohr, Niels, 110 Branch Davidians, 34, 219–220 Browning, Iben, 86 – 87, 94 Caddo Lake, 113–115, 251 Cambois, Guillaume, 65 champagne trick, 65– 66, 79– 80 chemical waste disposal, 36, 72–74 convection, 67– 68 Coons, Burton C., 256 crackpots, 86 – 88, 94, 256 damage: intensiﬁed, on dried lakebeds and reclaimed land, 62, 64 Davis, Scott, ix, 109–110 Delaware Basin, 23, 26, 198 Diablo Plateau, 20 –21 Doser, Diane, 23, 111 earthquake control, 73 earthquake hazard, in Texas, 37–39 in the United States, 38–39 earthquake kitsch aftershock liqueur, 97 bowling ball, x Balcones Fault beer, 35 chocolate cake, 96 Swenson’s ice cream, 102 wine, 225–226 earthquakes and weather, 78, 116, 126 –129, 178 earthquakes, causes of, 65– 81, 240 –250 ﬂuid injection, 71–75 petroleum production, 23–24, 29, 31, 33, 36, 74 –75, 81, 103, 131, 139, 144, 163, 175, 178, 189, 201–203, 207, 209, 215 plate tectonics, 59, 66 – 67 reservoirs, 31, 46, 71, 76 –78, 182–183, 189, 208, 211, 214

tidal forces, 63, 78, 86 volcanoes, 32, 47– 48, 70, 93, 125, 144 earthquakes, by characteristics caused by human activities, 70 –78 damaging (very), 44, 60 damaging (economically), 44 extraterrestrial, 61– 63 felt at greatest distance, 56 –57 frequency, 23, 54 large, but with few fatalities, 57 largest deep, 57–58 largest ever, 53–54 largest possible in northwestern U.S., 47 largest possible, 54 –56 largest in Texas, 20 –21, 147–154, 222 largest in U.S., 40 mislocated, 201, 204, 208, 254, 255 most deadly in twentieth century, 60 most deadly in U.S., 43 most deadly of all time, 60 most signiﬁcant, 60 – 61 second largest in Texas, 17, 222–228 small (laughably), 50 earthquakes, reported, by year 1556 —China, 60 1700 (Jan. 26)—northwestern U.S., 47, 56 1755 (Nov. 1)—Lisbon, Portugal, 60 – 61 1755 (Nov. 18)—New England, 50 1811–1812—New Madrid, MO, 5, 26, 29– 30, 36, 42– 43, 49, 69, 100, 106 –107, 112–115, 251 1847—Seguin, TX, 115, 240 1850s—Austin, TX (spurious), 115–116, 253 1857 (Jan. 9)—California, 42– 44, 83 1868 (April 2)—Hawaii, 42, 47– 48 1873 (May 1)—Manor, TX, 116 –117, 241 1882 (Oct. 22)—Fort Gibson, OK, 29, 117– 120, 251 1886 (Sept. 1)—Charleston, SC, 49, 69, 120 – 121, 251 1887 (Jan. 5)—Paige, TX, 32–34, 121–122, 241 1887 (Jan. 31)—Wellborn, TX, 123, 241 1887 (May 3)—Sonora, Mexico, 123–125, 251 1889 (May 31)—El Paso, TX, 19, 125–126, 241 1891 (Jan. 8)—Rusk, TX, 126 –127, 241 1891 (May 8)—Port Lavaca, TX, 253

269

1894 (Aug. 31)—Uvalde, TX (ﬂood), 127– 129, 253 1895 (Oct. 31)—New Madrid, MO, 49, 115, 251 1902 (Oct. 9)—Creedmoor, TX, 32–34, 107, 129–130, 241 1906 —Socorro, NM, 130, 251 1906 (April 18)—San Francisco, CA, 6, 40, 43– 44, 49, 64, 83 1907 (April)—Amarillo, TX, 28, 130 –132, 135, 253 1910 (May 8)—Hempstead, TX, 33–34, 132– 134, 241, 253 1914 (Dec. 30)—Anderson, TX, 134, 241 1915 (Oct. 2)—Nevada, 43, 45 1917 (March 28)—Panhandle, TX, 28, 131, 134 –137, 241, 253 1923 (March 7)—El Paso, TX, 19, 137–138, 241 1923 (Sept. 1)—Japan, 52, 59– 60 1925—Goose Creek, TX, 139, 253 1925 (July 29)—Silverton, TX, 139–140, 242 1925 (July 30)—Panhandle, TX, 24, 27, 135, 140 –145, 242, 254 1925 (July 31)—White Deer, TX, 145, 242 1928 (Nov. 1)—Mexico, 145–146, 251 1931 (Aug. 16)—Valentine, TX, xi, 1, 21–22, 40, 147–154, 222, 242–243 1931 (Oct. 2)—El Paso, TX, 19, 154, 243 1932 (April 9)—Wortham-Mexia, TX, 30 –31, 154 –156, 243 1934 (April 12)—Trout Switch, TX, 30, 156 – 158, 235, 243 1934 (Dec. 31)—Baja California, 158–159, 254 1935 (July 3)—Padre Island, TX (spurious), 159, 254 1936 (March 14)—Valliant, OK, 159–160, 251 1936 (June 19)—Clarendon, TX, 160, 243 1936 (June 20)—Borger, TX, 24, 27, 160 – 163, 243 1936 (Aug. 8)—El Paso, TX, 19, 163–164, 244 1936 (Oct. 15)—El Paso, TX, 19, 164, 244 1937 (March 31)—El Paso, TX, 19, 164 –165, 244 1937 (Aug. 8)—El Paso, TX (spurious), 165, 254 1938 (Sept. 17)—New Madrid, MO, 115 270

1939—Lake Mead, 76 1940 (May 19)—California, 44 1942, 1948—Alpine, TX, 165–166, 254 1946 (June 23)—British Columbia, 46 1948 (March 12)—Dalhart, TX, 24, 28, 166 – 168, 244 1949 (April 13)—Washington, 44, 46 1950 (March 20)—Chico, TX, 168, 244 1951 (June 20)—Amarillo, TX, 169–171, 244 1952 (April 9)—El Reno, OK, 29, 171–173, 252 1952 (July 21)—California, 43– 44 1952 (Oct. 17)— Orange, TX, 173–174, 244 1955 (Jan. 27)—Valentine, TX, 174, 244 1956 (Jan. 7)—Galveston, TX (sonic booms), 175, 254 1956 (Oct. 30)—Catoosa, OK, 175–176, 254 1957 (March 9)—Alaska, 42, 57 1957 (March 19)—Gladewater, TX, 30 –31, 127, 176 –178, 244 1959 (Feb. 10)—Panhandle, TX (sonic booms), 79– 80, 178–180, 255 1959 (June 17)—Lawton, OK, 180, 252 1959 (Aug. 18)—Hebgen Lake, MT, 40, 43, 45– 46, 48, 69 1960 (May 22)—Chile, 6, 54 –56, 59 1964 (March 28)—Alaska, 40, 42, 44, 49, 54 –57, 59, 181, 252 1964 (April–Aug.)—Hemphill-Pineland, TX, 30 –31, 181–184, 244 –245 1965 (Feb. 4)—Alaska, 42 1965 (April 29)—Washington, 46 1965 (Aug. 30)—Kermit, TX, 184, 245 1966 —Beaumont–Port Arthur, TX (sonic booms), 184 –187, 255 1966 (July 20)—Borger, TX, 187–189, 245 1966 (Aug. 14)—Kermit, TX, 23, 189–190, 245 1967—Denver, CO, 72–73 1967 (Dec. 10)—Koyna, India, 76 1969 (May 12)—El Paso, TX, 19, 191, 246 1969 (June)—Houston, TX (sonic booms), 191–192, 255 1970 (Jan. 12)—Amistad, NM, 192–193, 252 1970 (Feb. 3)—Travis Peak, TX (sonic booms or explosions), 193, 255 1971 (July)—Kermit, TX, 193–194, 246 1971 (Oct. 1)—Arkansas, 194, 255 1971 (Oct. 1)—New Madrid, MO, 115

T E X A S E A RT H Q UA K E S

1972 (Dec.)—El Paso, TX, 19, 195–196, 216, 246 1972 (Dec. 23)—Managua, Nicaragua, 60, 62, 64 1973 (Dec. 25)—Fashing, TX, 196 –197, 246 1974 (Feb. 15)—Perryton, TX, 28, 188, 197– 198, 246 1974 (June 24)—Fashing, TX, 208 1975 (Feb. 4)—Haicheng, China, 82– 85, 90 1975 (Aug. 1)—Delaware Basin, TX, 198– 199, 246 1975 (Nov. 29)—Hawaii, 47 1976 —Gazli, USSR, 75 1976 (Jan.)—Kermit, TX, 23, 199–200, 247 1976 (March 11)—Rhode Island, 50 1976 (April)—Durham, OK, 29, 200, 252 1976 (July 27)—Tangshan, China, 58, 60, 84 – 85 1977 (April 26)—Kermit, TX, 23, 200 –201, 247 1978 (March 2)—Kermit, TX, 23, 201, 247 1978 (June 16)—Snyder, TX, 24 –25, 148, 201–202, 207, 215, 247 1979 (July 5)—Snyder, TX, 203, 207 1980 (June 9)—Pampa, TX, 25, 27, 203–204, 247 1981 (June 9)—Center, TX, 204, 247 1981 (Nov. 6)—Jacksonville, TX, 127, 204206, 247 1982 (Jan. 4)—Fort Stockton, TX, 206, 248 1982 (March 28)—Fashing, TX, 208, 248 1982 (Oct. 14)—Dalhart, TX, 206 –207, 248 1982 (Nov. 28)—Snyder, TX, 207, 248 1983 (July 23)—Fashing, TX, 127, 207–209, 218, 248 1983 (Oct. 28)—Idaho, 43, 48 1983 (Oct. 29)—Lake Charles, LA, 174 1984 —Gazli, USSR, 75 1984 (March, Aug.)—Pleasanton, TX, 34, 209–210, 248 1984 (April 3)— Oldham County, TX, 29, 248 1985 (Sept. 18)—Valley View, TX, 210 –211, 248 1985 (Sept. 19)—Michoacan, Mexico, xi, 62, 212–213, 252 1986 (Jan. 30)—Silver, TX, 78, 214, 249 1987 (Jan. 15)—Rotan, TX (sonic booms), 215, 255 1989 (May 23)—Macquarie Ridge, 57, 59 INDEX

1989 (Oct. 18)—Loma Prieta, CA, 44, 62, 93 1990 (Jan. 19)—Maryland, 50 –51 1991 (July 20)—Falls City, TX, 209, 215– 216, 249 1992 (Jan. 2)—Rattlesnake Canyon, TX, 23, 148, 192, 216 –217, 249 1992 (June 28)—Landers, CA, 43– 44, 93 1992 (Aug. 10)—Jourdanton, TX, 217–218 1992 (Oct. 20)—Parkﬁeld, CA, 87 1993 (April 9)—Fashing, TX, 33–34, 218– 220, 249 1993 (May 16)—Jourdanton, TX, 220 –221, 249 1993 (Sept., Nov.)—Amistad, NM, 221, 252 1994 (Jan. 17)—Northridge, CA, 44, 93 1994 (June 9)—Bolivia, 57–59, 63 1995 (Jan. 4)—Hallettsville, TX, 221–222 1995 (Jan. 16)—Kobe, Japan, 93 1995 (April 14)—Alpine, TX, ix, 17–18, 21– 22, 148, 222–232, 249 1995 (Dec. 15)—Coleman, TX (spurious), 232, 255 1996 –1997—McClean, TX, 232–233, 250 1997 (March 24)—Alice, TX, 33, 37, 233– 235, 250 1997 (May 31)—Commerce, TX, 157, 235– 236, 250 1998 (March 25)—Balleny Island, 4 –5, 6, 57, 59 1998 (April 15)—Alpine, TX, 236, 250 1998 (April 28)—Lawton, OK, 237, 252 1999 (Sept. 20)—Taiwan, 54 1999 (Oct. 15)—Hector Mine, CA, 44 2000 (Aug. 2–17)—Amarillo, TX, 237–239, 250 2000 (Dec. 16)—Amarillo, TX, 239, 250 2001 (Feb. 28)—Seattle, 44, 46 earthquakes, reported, by location Alaska (March 9, 1957), 42, 57 Alaska (March 28, 1964), 40, 42, 44, 49, 54 –57, 59, 181, 252 Alaska (Feb. 4, 1965), 42 Alice, TX (March 24, 1997), 33, 37, 233– 235, 250 Alpine, TX (1942, 1948), 165–166, 254 Alpine, TX (April 14, 1995), ix, 17–18, 21– 22, 148, 222–232, 249 Alpine, TX (April 15, 1998), 236, 250 Amarillo, TX (April 28, 1907), 28, 130 –132, 135, 253 271

Amarillo, TX (June 20, 1951), 169–171, 244 Amarillo, TX (Aug. 2–17, 2000), 237–239, 250 Amarillo, TX (Dec. 16, 2000), 239, 250 Anderson, TX (Dec. 30, 1914), 134, 241 Arkansas (Oct. 1, 1971), 194, 255 Austin, TX (1850s; spurious), 115–116, 253 Baja California (Dec. 31, 1934), 158–159, 254 Balleny Island (March 25, 1998), 4 –5, 6, 57, 59 Beaumont–Port Arthur, TX (1966; sonic booms), 184 –187, 255 Bolivia (June 9, 1994), 57–59, 63 Borger, TX (June 20, 1936), 24, 27, 160 –163, 243 Borger, TX (July 20, 1966), 187–189, 245 California (Jan. 9, 1857), 42– 44, 83 California (May 19, 1940), 44 California (July 21, 1952), 43– 44 California—Hector Mine (Oct. 15, 1999), 44 California—Landers (June 28, 1992), 43– 44, 93 California—Loma Prieta (Oct. 18, 1989), 44, 62, 93 California—Northridge (Jan. 17, 1994), 44, 93 California—Parkﬁeld (Oct. 20, 1992), 87 California—San Francisco (April 18, 1906), 6, 40, 43– 44, 49, 64, 83 Canada—British Columbia (June 1946), 23, 46 Center, TX (June 9, 1981), 204, 247 Chico, TX (March 20, 1950), 168, 244 Chile (May 22, 1960), 5, 54 –56, 59 China (1556), 60 China—Haicheng (Feb. 14, 1975), 82– 85, 90 China—Tangshan (July 28, 1976), 58, 60, 84 – 85 Clarendon, TX (June 19, 1936), 160, 243 Coleman, TX (Dec. 15, 1995; spurious), 232, 255 Colorado—Denver (1967), 72–73 Commerce, TX (May 31, 1997), 157, 235– 236, 250 Creedmoor, TX (Oct. 9, 1902), 32–34, 107, 129–130, 241 Dalhart, TX (March 12, 1948), 28, 166 –168, 244 Dalhart, TX (Oct. 14, 1982), 206 –207, 248 272

Delaware Basin, TX (Aug. 1, 1975), 198–199, 246 El Paso, TX (May 31, 1889), 19, 125–126, 241 El Paso, TX (March 7, 1923), 19, 137–138, 241 El Paso, TX (Oct. 2, 1931), 19, 154, 243 El Paso, TX (Aug. 8, 1936), 19, 163–164, 244 El Paso, TX (Oct. 15, 1936), 19, 164, 244 El Paso, TX (Aug. 8, 1937; spurious), 165, 254 El Paso, TX (March 31, 1937), 19, 164 –165 El Paso, TX (May 12, 1969), 19, 191, 246 El Paso, TX (Dec. 19, 1972), 195–196, 216, 246 Falls City, TX (July 20, 1991), 209, 215–216, 249 Fashing, TX (Dec. 25, 1973), 196 –197, 246 Fashing, TX (June 24, 1974), 208 Fashing, TX (March 28, 1982), 208, 248 Fashing, TX (July 23, 1983), 127, 207–209, 218, 248 Fashing, TX (April 9, 1993), 33–34, 218– 220, 249 Fort Stockton, TX (Jan. 4, 1982), 206, 248 Galveston, TX (Jan. 7, 1956; sonic booms), 175, 254 Gladewater, TX (March 19, 1957), 30 –31, 127, 176 –178, 244 Goose Creek, TX (1925), 139, 253 Gulf of Mexico (1960, 1978), 71 Hallettsville, TX (Jan. 4, 1995), 221–222 Hawaii (April 2, 1868), 42, 47 Hawaii (Nov. 29, 1975), 47– 48 Hemphill-Pineland, TX (1964), 30 –31, 181– 184, 244 –245, 253 Hempstead, TX (May 8, 1910), 33, 132–134, 241 Houston, TX (June 1969), 191–192, 255 Idaho (Oct. 28, 1983), 43, 48 India—Koyna (Dec. 10, 1967), 76 Jacksonville, TX (Nov. 5, 1981), 127, 204 – 206, 247 Japan (Sept. 1, 1923), 52, 59– 60 Japan (Jan. 16, 1995), 93 Jourdanton, TX (Aug. 10, 1992), 217–218 Jourdanton, TX (May 16, 1993), 220 –221, 249 Kermit, TX (Aug. 30, 1965), 184, 245

T E X A S E A RT H Q UA K E S

Kermit, TX (Aug. 14, 1966), 23, 189–190, 245 Kermit, TX (July 1971), 193–194, 246 Kermit, TX (Jan. 23, 1976), 199–200, 246 Kermit, TX (April 26, 1977), 23, 200 –201, 246 Kermit, TX (March 2, 1978), 23, 201, 248 Lake Mead (1939), 76 Louisiana—Lake Charles (Oct. 29, 1983), 174 Macquarie Ridge (May 23, 1989), 57, 59 Manor, TX (May 1, 1873), 116 –117, 241 Maryland (Jan. 19, 1990), 50 –51 McClean, TX (1996 –1997), 232–233, 250 Mexico (Nov. 1, 1928), 145–146, 251 Mexico—Michoacan (Sept. 19, 1985), xi, 62, 212–213, 252 Mexico—Sonora (May 3, 1887), 123–125, 251 Montana—Hebgen Lake (Aug. 18, 1959), 40, 43, 45– 46, 48, 69 Nevada (Oct. 2, 1915), 43, 45 New England (Nov. 18, 1755), 50 New Madrid, MO (1811–1812), 5, 26, 29–30, 36, 42– 43, 49, 69, 100, 106 –107, 112– 115, 251 New Madrid, MO (Oct. 31, 1895), 49, 115, 251 New Madrid, MO (Sept. 17, 1938), 115 New Madrid, MO (Oct. 1, 1971), 115 New Mexico—Amistad (Jan. 12, 1970), 192–193, 252 New Mexico—Amistad (Sept. /Nov. 1993), 221, 252 New Mexico—Socorro (1906), 130, 251 Nicaragua (Dec. 23, 1972), 60, 62, 64 northeast Texas, 29–32, 37 northwestern U.S. (Jan. 26, 1700), 47, 56 Oklahoma—Catoosa (Oct. 30, 1956), 175– 176, 254 Oklahoma—Durham (April 29, 1976), 200, 252 Oklahoma—El Reno (April 9, 1952), 29, 171–173, 252 Oklahoma—Fort Gibson (Oct. 22, 1882), 29, 117–120, 251 Oklahoma—Lawton (June 17, 1959), 180, 252 Oklahoma—Lawton (April 28, 1998), 237, 252 INDEX

Oklahoma—Valliant (March 14, 1936), 159– 160, 251 Oldham County, TX (April 3, 1984), 29, 248 Orange, TX (Oct. 17, 1952), 173–174, 244 Padre Island, TX (July 3, 1935), 159, 254 Paige, TX (Jan. 5, 1887), 32–34, 121–122, 241 Pampa, TX (June 9, 1980), 25, 27, 203–204, 248 Panhandle, 24 –29, 37, 105–106 Panhandle, TX (March 28, 1917), 28, 131, 134 –137, 241, 254 Panhandle, TX (July 30, 1925), 24, 27, 135, 140 –145, 242, 254 Panhandle, TX (Feb. 10, 1959; sonic booms), 79– 80, 178–180, 255 Perryton, TX (Feb. 15, 1974), 28, 188, 197– 198, 246 Pleasanton, TX (March/Aug. 1984), 34, 209– 210, 248 Port Lavaca, TX (May 8, 1891), 253 Portugal—Lisbon (Nov. 1, 1755), 60 – 61 Rattlesnake Canyon, TX (Jan. 2, 1992), 23, 148, 192, 216 –217, 249 Rhode Island (March 11, 1976), 50 Rotan, TX (Jan. 15, 1987; sonic booms), 215, 255 Rusk, TX (Jan. 8, 1891), 126 –127, 241 Seguin, TX (1847), 115, 240 Silver, TX (Jan. 30, 1986), 78, 214, 249 Silverton, TX (July 29, 1925), 139–140, 242 Snyder, TX (June 16, 1978), 24 –25, 148, 201–202, 207, 215, 248 Snyder, TX (July 5, 1979), 203, 207 Snyder, TX (Nov. 28, 1982), 207, 248 South Carolina—Charleston (Sept. 1, 1886), 49, 69, 120 –121, 251 south-central Texas, 32–37 Taiwan (Sept. 20, 1999), 54 Travis Peak, TX (Feb. 3. 1970; sonic booms), 193, 255 Trout Switch, TX (April 12, 1934), 30, 156 – 158, 235, 243 USSR—Gazli (1976 –1984), 75 Uvalde, TX (Aug. 31, 1894; ﬂood), 127–129, 253 Valentine, TX (Aug. 16, 1931), xi, 1, 21–22, 40, 147–154, 222, 242–243 Valentine, TX (Jan. 27, 1955), 174, 244 273

Valley View, TX (Sept. 18, 1985), 210 –211, 248 Washington (April 13, 1949), 44, 46 Washington (April 29, 1965), 46 Washington—Seattle (Feb. 28, 2001), 44, 46 Wellborn, TX (Jan. 31, 1887), 123, 241 West Texas, 18–24, 37, 106 White Deer, TX (July 31, 1925), 145, 242 Wortham-Mexia, TX (April 9, 1932), 30 –31, 154 –156, 243 Enchanted Rock, TX, 67, 70 explosions, 224 Big Spring—1929 (seismic blasting), 146 – 147, 254 Brenham (1992), 112, 221 nuclear, 104 possible, 211 quarry blasts, 79, 187–189 Texas City, 1947, 112 Waco, TX (Nov. 3, 1986), 214 –215 faults Amarillo-Wichita system, 24, 26, 28 Balcones, xi, 26, 33, 35 buried, 100, 144 Charlotte-Jourdanton, 26, 33 Luling, 26, 33 Mayﬁeld, 20 –21 Meers, 27, 237 Mexia-Talco system, 26, 33, 122 Mt. Enterprize zone, 26, 127 Rim Rock, 20 –21 Rio Grand Rift, 19, 26 San Andreas, 83, 88 Valentine, 21 Wasatch, 48 Federal Emergency Management Agency, xv, 18 Flawn, Peter, xv ﬂoods 1894 (Uvalde, TX), 127–129, 253 1981 (Austin, TX), 95 ﬂuid injection to dispose of chemical wastes, 36, 72–74 earthquakes induced by, 71–75 focal mechanisms, 148, 198, 202, 216, 222 foreshocks, 88– 89, 91–92, 160 Borger, TX (1936), 160 Panhandle, TX (1925), 140 –141

274

Valentine, TX (1931), 21, 152–153, 256 Frohlich, Chovy, xv, xvi Frohlich, Cliff, ix, 107–110 Frohlich, Tom, xv, xvi geology map with structural features of Texas, 26 with structural features of West Texas, 20 Gutenberg, Beno, 109 Gutenberg-Richter law, 23 Hoffenberg, Mason, 61 Hoover Dam, 76 Hueco Bolson, 20 hurricanes, 93–95, 101 insurance, earthquake, 95–98, 142 intensity, Mercalli, 1– 4 Lake Mead, 76 landslides caused by earthquakes 1887 (May 3)—Sonora, Mexico, 123, 125 1914 (Dec. 30)—Anderson, TX, 134 1931 (Aug. 16)—Valentine, TX, 149, 242 1959 (Aug. 18)—Hebgen Lake, MT, 45 1985 (Sept. 19)—Michoacan, Mexico, 212 1994 (June 9)—Bolivia, 63 1995 (April 14)—Alpine, TX, 18, 223, 249 Lehmann, Inge, 110 Llano Uplift, 26, 33 magnitude, 4 – 6, 8, 112–113 explanation of different, 6, 113 relationship of, to fault properties, 9 relationship of, to moment, 8–10 scales, 6, 113 Marathon Uplift, 20, 22 marsquakes, 62, 64 McClellan, Zelda, 232–233 Mercalli, Guiseppe, 1 Midland Basin, 23, 26 Milne, John, 109 moment relationship of, to fault properties, 9 relationship of, to magnitude, 8–10 scalar, 7–10 moonquakes, 61– 63 Nakamura, Yosio, 63

T E X A S E A RT H Q UA K E S

seismic waves, 7 P waves, 10 –12 S waves, 10 –12 surface waves, 11 seismograph how it works, 10 –14 stations in Texas, 15 stations operated by amateurs, 16 seismologists most famous, 109–111 training of, 107–109 what they do, 104 –107 what they study, 103–104 sonic booms, 79– 80, 256 Sputnik, 107 Stewart, David, 87

oil and gas ﬁelds Cogdell, 24, 201, 203, 207 East Texas, 31, 178 Fashing, 218–219 Goose Creek, 139 Imogene, 209 Kermit, 24 Mexia, 31 Panhandle, 27, 189 Stratton, 37 War Wink, 23 Wortham, 31 Ortiz, Juan, 20, 137 Ouachita Belt, 26 –27, 30 Pat Mayse Lake, 31 Pennington, Wayne, xv plate tectonics, 59, 66 – 67 precursors to earthquakes animal behavior, 83, 90 –92 electromagnetic signals, 87, 89, 91–92 foreshocks, 84 – 85, 88– 89, 91–92 groundwater changes, 83, 89, 92 radon gas, 89–90 tilting of the ground, 89 well level changes, 84 predicting earthquakes, 82–94 future of, 92–94 most successful example of, 82– 84

termites, 98 Texas Division of Emergency Management, xv, 18, 24, 29, 32 tsunamigenic earthquakes, 54, 57, 101 Alaska (1964), 40, 57 Chile (May 22, 1960), 57 Hawaii (April 2, 1868), 48 Lisbon, Portugal (Nov. 1, 1755), 60 – 61 Mexico (Sept. 19, 1985), 62 New England (Nov. 18, 1755), 50 northwestern U.S. (Jan. 26, 1700), 47, 56 tsunamis, 101 Urbanczyk, Kevin, 225 Uyeda, Seiya, 94

Reelfoot Rift, 26 Reid, Harry F., 132–133 Richter, Charles, 5, 109 Rocky Mountain Arsenal, 72–73 Romanowicz, Barbara, 111

VAN prediction method, 87– 88

Scholz, Chris, 92 seiches caused by earthquakes 1964 (March 28)—Alaska, 181, 252 1985 (Sept. 19)—Michoacan, Mexico, 212, 252

INDEX

Wadati, Kiyoo, 109–110 Warren Petroleum plant, 218 water wells affected by earthquakes 1886 (Sept. 1)—Charleston, SC, 120 –121 1931 (Aug. 16)—Valentine, TX, 150 1964 (March 28)—Alaska, 181

275

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