Earthquake Hazard In Lebanon

EARTHQUAKE

• HAZARD IN.%

LEBANOIN Amr Salah-Eldin Elnashai Ramy El-Khoury

Imperial College Press

About the Authors Amr Salah-EIdin Elnashai Fellow of the Royal Academy of Engineering in the UK, Amr is the Willett Professor of Engineering at the University of Illinois at Urbana-Champaign and the Director of the Mid-America Earthquake Center. He is a Fellow of the American Society of Civil Engineers and the UK Institution of Structural Engineers. A graduate of Cairo University, he obtained his MSc and PhD from Imperial College, University of London. Before joining the University of Illinois in 2001, Amr was Professor of Earthquake Engineering and Head of the Engineering Seismology and Earthquake Engineering Section at the Imperial College. He is the founder and co-editor of the Journal of Earthquake Engineering, a member of the drafting panel of the European seismic design code and the past senior Vice-President of the European Association of Earthquake Engineering. Amr has been a Visiting Professor at the University of Surrey in the UK since 1997. Other visiting appointments include the University of Tokyo, the University of Southern California and the European School for Advanced Studies in Reduction of Seismic Risk, Italy. He has worked in the field and reported on most of the damaging earthquakes around the world since the mid-eighties.

Ramy El-Khoury Ramy graduated from the Imperial College, University of London, with a BSc in civil engineering followed by a Master of Science in Earthquake Engineering and Structural Dynamics. He is a Member of the Institution of Civil Engineers, UK and the Order of Engineers & Architects. A Civil Engineer, specializing in Earthquake Engineering and Structural Dynamics, he is involved in the design, construction supervision and/or management of major infrastructure and building projects for Rafik El-Khoury & Partners, one of the top multidisciplinary consulting engineering firms in Lebanon. He is a participant in the RELEMR Program (Reducing Earthquake Losses in the Eastern Mediterranean Region) sponsored by UNESCO, the United States Geological Survey, the Council of Europe and the European Mediterranean Seismic Center. He is a member of the Global Alliance for Disaster Reduction in charge of organizing the World Congress on Disaster Reduction.

This page is intentionally left blank

HAZARD IN,.

EBANOlN Amr Salah-Eldin Elnashai University of Illinois at Urbana-Champaign, USA

Ramy El-Khoury Rafik El-Khoury & Partners, Lebanon

Imperial College Press

Published by Imperial College Press 57 Shelton Street Covent Garden London WC2H 9HE Distributed by World Scientific Publishing Co. Pte. Ltd. 5 Toh Tuck Link, Singapore 596224 USA office: Suite 202, 1060 Main Street, River Edge, NJ 07661 UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library.

EARTHQUAKE HAZARD IN LEBANON Copyright © 2004 by Imperial College Press All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the Publisher.

For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher.

ISBN 1-86094-461-2

Editor: Tjan Kwang Wei

Printed in Singapore by World Scientific Printers (S) Pte Ltd

Acknowledgements This book which comprises the most comprehensive earthquake hazard study undertaken to date for Lebanon has been made possible through the vision, financial support and national consciousness of Messrs. Fouad, M. Malouf and Farouk W. Agha who have taken the initiative in commissioning this work through the services of Rafik El-Khoury & Partners - Consulting Engineers, Lebanon, who acted as Project Managers and who have allowed the technical team complete freedom to carry out an as elaborate and verified study as possible. This book comprises the scope of work undertaken by Professors A.S. Elnashai (University of Illinois, USA - as contributor, research manager and technical editor), Professor N.N. Ambraesys (Imperial College, UK historical seismicity and earthquake catalogue), Dr. J. Jackson (Cambridge University, UK - plate tectonics), Dr. S.K. Samra (Imperial College, UK seismic hazard), Mr. R.R. El-Khoury (Rafik El-Khoury & Partners, Lebanon - project management, scope definition and report production) and Mr. G. Cossenas (Imperial College, UK - GIS applications and production). During the course of the project, the team enjoyed the support and contribution of Mr. Ramy El-Khoury whose role in rounding-up the study in its final form was essential. The technical editor of this book, Prof. Amr Elnashai, would like to personally thank all the above, and also his co-workers who executed their respective role professionally and diligently and worked to strict guidelines uncharacteristic of Academics.

This page is intentionally left blank

Table of Contents Chapter 1

Executive Summaries 1.1 Non-Specialist 1.2 Specialist Chapter 2 Background to the Study Chapter 3 Earthquake Hazard — Preliminaries 3.1 Active Tectonics of the Levant and Dead Sea Fault Zone 3.2 Historical Seismicity 3.3 Estimates of Rates 3.4 Twentieth Century Seismicity of the Levant and Lebanon Chapter 4 Magnitude Recurrence in Lebanon and Adjacent Regions Chapter 5 Synthesis of Seismicity and Rate Information Chapter 6 Selection of Attenuation Relationship 6.1 Peak Ground Acceleration (PGA) 6.2 Peak Ground Displacements (PGD) 6.3 Acceleration Response Spectra (SA) 6.4 Displacement Response Spectra (SD) Chapter 7 Source Zone Modelling and Recurrence Relationship 7.1 Completeness Test 7.2 Source Zone Modelling 7.3 Dead Sea Rift Zone 7.4 East Anatolian Fault Zone 7.5 Yammouneh Fault Zone 7.6 Maximum Magnitudes Chapter 8 Hazard Maps 8.1 Peak Ground Accelerations (PGA) 8.2 Peak Ground Displacements (PGD) 8.3 Spectral Accelerations (SA) and Spectral Displacements (SD) Chapter 9 Site-Specific Hazard Assessments 9.1 City of Beirut 9.2 City of Tripoli 9.3 CityofSidon vn

1 1 2 5 9 9 21 40 42 49 59 63 63 66 67 67 69 69 70 75 76 78 79 81 81 82 82 83 83 87 90

Vlll

Elnashai and El Khoury

Chapter 10 Deterministic Assessment of Seismic Hazard Chapter 11 Concluding Remarks on Seismic Hazard in Lebanon Appendix Al: Surface Wave Magnitude Appendix A2: Application of Stepp Method Appendix A3: Hazard Maps for Lebanon and Vicinity References

95 101 109 119 121 157

Chapter 1

Executive Summaries

1.1

Non-Specialist

This report presents a thorough assessment of the hazard from earthquakes in Lebanon in terms of the levels of ground shaking to be considered in design of structures. The assessment is carried out by developing a model to represent the occurrence of earthquakes in Lebanon and surrounding areas. The model for the location of potential future earthquakes is based on the concentration of earthquake activity at the boundaries of major plates of the earth's crust. In the case of the Levant, the geographic limit of interest is the Dead Sea Rift, which marks the boundary between the African and Arabian tectonic plates. This plate boundary is marked within the Lebanon by the Yammouneh fault. The model also includes the possibility of other faults, such as the Roum fault, producing earthquakes. More distant plate boundaries in the Mediterranean and in southeast Turkey are also included. The data used to calculate the earthquake hazard is an extensive and carefully re-evaluated catalogue of earthquakes in the Levant from 303 AD to the 20th century. To express the hazard in an form suitable for engineering design, the model for earthquake occurrence is combined with equations that predict values of the peak acceleration and displacement of the ground. These equations are used to calculate the levels of ground motion that would result at a large number of locations from all of the potential earthquakes represented by the model described above. These results are used to calculate the levels of ground acceleration and displacement at each location for three different return periods, which correspond to three different performance levels for structures. The three return periods represent small frequent and large rare

1

2

Elnashai and El Khoury

earthquakes as well as earthquakes of intermediate size and frequency of occurrence. Contour maps are drawn for both acceleration and displacement, for the three return periods, providing a useful and reliable representation of the distribution and level of earthquake hazard throughout Lebanon. These maps correspond to sites with average soil conditions. In order to provide a more complete representation of the hazard in the three major cities of Beirut, Sidon and Tripoli, the hazard in these three cities is presented in the form of response spectra for rock, stiff soil and soft soil sites, which is the form used by modern earthquake design codes. These results allow the direct determination of seismic design loads in these three cities and also serve to illustrate the variation of the hazard level for different soil conditions for other locations in Lebanon. The results of the extensive study are represented in a simple form, giving approximate percentages of building weight to be applied horizontally during the design process. 1.2

Specialist

The report presents a comprehensive evaluation of seismic hazard in Lebanon suitable for use as the basis for earthquake-resistant design of structures. The framework for the quantitative assessment of seismic hazard in Lebanon is established from the state-of-the-art regarding the understanding of active tectonics in the Levant and surrounding regions. The model for the current tectonic processes affecting Lebanon is based on recently published studies, focal mechanisms of earthquakes in the region and GPS measurements of deformation vectors. The principal tectonic process affecting seismicity in and around the Lebanon is the relative motion of the African and Arabian lithospheric plates, which are separated by the Dead Sea Rift. This boundary is manifested primarily by the Yammouneh fault within Lebanon, but also, significantly by a series of smaller faults that branch from the Yammouneh fault, including the Roum fault that approaches Beirut. To a lesser extent, the Lebanon is also affected by the

Earthquake Hazard in Lebanon

3

subduction of the African plate below the Eurasian plate in the Cyprus arc and triple junction of the African, Arabian and Eurasian plates in southeast Turkey. The seismicity of the Lebanon and surrounding areas has been uniformly re-evaluated and descriptions of the felt and damaging effects of events in the region dating from 303 A.D. are presented. For the largest historical earthquake events during the last 1000 years, both locations and magnitudes have been assessed from the macroseismic data recovered from primary sources. This data provides a very important insight into both the active seismogenic structures affecting the country, the long-term recurrence rates and the maximum expected earthquake magnitudes. For the twentieth century, source parameters for earthquakes in the Levant have been uniformly re-assessed to provide a definitive seismicity catalogue for the region. The framework of tectonic processes and the revised earthquake catalogues, have been used to define seismic source zones that model the generation in space and time of earthquake events that influence the Lebanon. Conservative assumptions regarding the geographical boundaries of these regions are made where there is uncertainty or incomplete data in order to avoid underestimation of the potential earthquake threat in any part of the country. Attenuation relationships for the prediction of peak ground acceleration and displacement, and for the response spectral ordinates of acceleration and displacement, have been selected. These relationships are based on large, high-quality strong-motion datasets that include many earthquake recordings from the Middle East. An established probabilistic seismic hazard methodology is then applied to produce contour maps of the variation of selected ground-motion parameters for average soil conditions and three different return periods, applicable to different structural performance levels. These maps provide a realistic representation of the distribution of earthquake hazard in Lebanon and reflect the important

4

Elnashai and El Khoury

influence of large magnitude events, of long return period, that can be expected on the Yammouneh fault despite the relatively low activity of this source during the last 100 years. For the three principal cities in Lebanon, Beirut, Sidon and Tripoli, hazard assessments have been performed to derive response spectra of both acceleration and displacement for three site categories (rock, stiff soil and soft soil) and for three return periods (475, 1000 and 2500 years). These allow the basic input to seismic design at any site within these cities to be defined, following a classification of the soil profile through appropriate borehole investigations.

Chapter 2

Background to the Study

On a public awareness level, seismic hazard and risk in Lebanon is not wellknown. This is mainly due to the long return period of earthquakes in this region, with infrequent but seriously damaging earthquakes. The region is currently undergoing total transformation, as a consequence of the relative political stability that Lebanon has enjoyed recently after years of political and social strife. A most ambitious building programme is underway, funded by internal and external sources. In such situations, it is often the case that considerations of medium term hazard from natural disasters are ignored in favour for economic development and rapid construction. It is clear that Lebanon, whilst experiencing an economic uprising, the fabric of the economy and indeed society is still fragile. An increased awareness of the hazard from natural disasters, especially earthquakes, is therefore of great significance, in order that the case for a more considered approach towards design and construction of new facilities and structures is stressed. It is mainly to raise awareness as well as provide the best available technical data on earthquake risk that these series of studies have been initiated. This book is Phase I of a multi-phase programme covering the following: Hazard: A comprehensive study of seismic hazard in Lebanon and neighbouring areas, using most recent techniques of hazard assessment and utilising the best available data from the area and other areas around the world with similar seismo-tectonic environments. Modern trends of deterministic hazard assessment and representation in terms of parameters other than acceleration or intensity are considered. The outcome is the current book. It summarises the findings in easy forms understandable by well-informed individuals with no earthquake engineering background. It will also serve as a platform for subsequent studies, as detailed below.

5

6

Elnashai and El Khoury

Infrastructure: Guidelines to identify and remedy commonly-occurring defects in masonry and RC structures of configurations typical of Lebanon using readily available material and expertise. Although the technical source of this manual is of a very high quality and the justification for the action recommended is in the domain of advanced inelastic dynamic analysis, it should be presented in a from understandable and usable by a layman with minimum structural engineering knowledge. Visual Risk Assessment: The development of an integrated risk (hazard and vulnerability) system for the whole of Lebanon and neighbouring areas and its implementation to run on a basic PC with minimum configuration requirements. This tool would be easily demonstrated to politicians and decision-makers, who can use it on-line to visualise the effects of a hypothetical earthquake on buildings, bridges, hospitals, networks etc. The engine behind the screen will be robust and reflects the most modem trends in seismic risk assessment. Building Codes: The production of source documents that would be readily available for code drafting committees in Lebanon once the political will have been mobilised. These will include a document on new design concepts (based on best international practice from New Zealand-NZ1997, USA-UBC/IBS and Europe-EC8/NADs) and another on assessment, repair and strengthening (from USA-FEMA 273/274 and Europe-EC8 Part 1.4). The used technical information will be interpreted in practices and procedures compatible with Lebanese practice and construction heritage. This book is concerned with work package T described above, and deal with salient aspects of assessment of earthquake hazard (exposure) in Lebanon. A thorough review of earthquakes and their effects is provided in the book and its appendices, followed by a compilation of a rigorous earthquake catalogue. This is employed in probabilistic seismic hazard assessment leading to the derivation of contour maps of earthquake ground acceleration and displacement for three return periods, namely 475, 1000 and 2500 years. The study also includes derivation of spectral ordinates for

Earthquake Hazard in Lebanon

7

the same return periods for the purposes of seismic design, for a range of periods covering the majority of structural configurations. Finally, sitespecific studies are conducted for Sidon, Beirut and Tripoli as the three largest cities in Lebanon.

This page is intentionally left blank

Chapter 3

Earthquake Hazard - Preliminaries

Any advancement of our knowledge about the assessment and mitigation of earthquake hazard should be accompanied by a growth in our accumulation of reliable observational data and field information from past earthquakes. The purpose of this part of the book is, by combining instrumental and macroseismic information, to assess the location and to assign uniformly calculated surface-wave magnitudes to earthquakes in Lebanon and adjacent regions during the 20th century. The book draws on sources of macroseismic information, supplemented by re-examination of instrumental reports, to evaluate the position and size of significant earthquakes in Lebanon, in the region between latitudes 32° and 35° N and longitudes 35° and 37°E, and to examine the activity of an extended region between 27° to 37°N and 34° to 37°E which is traversed by the Dead Sea fault system that dominates the earthquake hazard in Lebanon. 3.1

Active Tectonics of the Levant and Dead Sea Fault Zone

The seismicity in the eastern Mediterranean results from the interactions between the major Africa, Arabia and Eurasia plates, Figure 3.1. Modern seismicity in the Levant is shown in Figure 3.2. Both Africa and Arabia are moving north relative to stable Eurasia, and east of about 40° E the high mountains of eastern Turkey and the Caucasus are a direct result of the collision between the Arabian and Eurasian continents, which started about 12 to 15 Ma ago (Dewey et al. 1986). As in many continental collision zones, there is little evidence for subduction of continental crust into the mantle, presumably because it is too buoyant, and the shortening leads to crustal thickening and mountain building instead. However, west of 40° E, stable Eurasia is separated from the stable Africa and Arabian plates by central

9

10

Elnashai and El Khoury

Turkey, which behaves as a rigid block or 'microplate' and moves west relative to Eurasia bounded by the North Anatolian and East Anatolian strike-slip fault zones (Figure 3.1). West of about 30° E the Turkish block starts to deform internally by distributed faulting that spreads across most of the Aegean Sea. The westward motion of Turkey is accommodated by subduction in the Hellenic Trench along the southern margin of Greece, so that Turkey and the Aegean over-ride the Mediterranean Sea floor, which subducts northwards beneath Greece and is responsible for the active volcanoes of the southern Aegean (e.g. Jackson 1994). Thus in the eastern Mediterranean the convergence between Eurasia and Africa-Arabia is achieved by the lateral expulsion of Turkey from the collision zone.

Earthquake Hazard in Lebanon

11

28*

32*

36*

40°

44°

28°

32*

38

40s

44s

Fig 3.1. Tectonic framework of the eastern Mediterranean. GPS velocity vectors are from McClusky et al. (2000) and are shown relative to Eurasia (Table 3.1 and Table 3.2). Solid lines show major faults, including the Dead Sea fault (DSF), North Anatolian fault (NAF) and East Anatolian fault (EAF). The Florence Rise is marked FR. Note the westward movement of central Turkey away from the collision zone between Arabia-Africa and Eurasia.

The dominant tectonic feature of the Levant is the Dead Sea Fault system (Garfunkel et al 1981), which is a zone of left-lateral strike-slip mnning from the Gulf of Aqaba to join the East Anatolian fault zone near Maras in SE Turkey.

Elnashai and El Khoury

12 28*

32*

36^

40*

44*

Fig 3.2. Summary of the modern seismicity. Small white circles are epicentres of earthquakes of mb > 5.2 from the catalogue of Engdahl et al. 1998 for the period 1964-1998. Black circles are earthquakes of M s > 5.7 from 1900-2000.

The Dead Sea fault zone accommodates about 8-10 mm/yr of slip between Arabia and Africa and has produced many large (Ms > 7) earthquakes in the past (e.g. Ambraseys and Melville 1988; Ambraseys and Barazangi 1989), though it has been relatively quiet in the 20th century. Its junction with the East Anatolian fault zone is diffused and poorly understood (Lyberis et al. 1994), and so is the connection between this region and Cyprus. Some E-W extension is expected in the Gulf of Iskenderan (Antakya) region (Jackson and McKenzie 1984) and is seen in the earthquake focal mechanisms (Figure 3.3 and Table 3.3).

Earthquake Hazard in Lebanon

13

Table 3.1: Plate models and expected rates (a) Expected Arabia-Africa velocities across the Dead Sea fault zone at 34°N 36°E (near Beirut) Az Vel DeMets et al. 1994 (NUVEL-1 A) 11.6 320 8.3 353 Joffe&Garfunkell987 Le Pichon & Gaulier 1998 9.1 357 354 Jesting al. 1994 8.9 (b) Expected and observed velocities of GPS sites relatives to Eurasia BARG TELA KATZ az vel az Vel Az vel 002 DeMets et al. 1994 (NUVEL-1 A) 002 10.3 10.3 19.9 342 itsimetal. 1994 19.8 001 11.4 345 349 358 6.0 8.9 GPS observed (McClusky et al. 2000) Velocities are in mm/yr. For the 'expected' velocities predicted by plate models, KATZ is assumed to be on the Arabian plate, and both BARG and TELA on the African plate.

Table 3.2: GPS velocities relative to Eurasia and lstandard deviation uncertainties (from McClusky et al. 2000). span Obs oc on Lon Lat Site Vn vc 2 1994.7-1996.8 1.5 -11.1 1.4 8.6 36.90 36.14 DORT 2 7.9 1994.7-1996.8 1.5 -5.4 1.4 36.05 36.13 SENK 1.7 2 9.0 1991.7-1994.8 -11.5 1.6 36.46 35.94 ULUC c 11.2 1997.8-1999.4 -2.2 2.3 2.2 KATZ 32.99 35.69 2.0 2 -0.2 6.0 1994.7-1996.8 1.9 31.72 35.09 BARG 1.8 2 1996.8-1998.2 -2.3 8.6 1.7 32.07 34.78 TELA Velocities and uncertainties are in mm/yr. Obs refers to the number of observation epochs: continuous stations are marked c. Span refers to the observation time span, with dates give in tenths of years.

14

Elnashai and El Khoury

Table 3.3: Source parameters of selected earthquakes in Figure 3.3

Mw Lat Lon Date %d-c 31.24 35.46 99.7 5.1 1979 04 23 35.16 1984 08 24 85.6 5.3 32.71 34.41 34.74 28.7 5.4 1993 03 22 34.64 29.25 79.7 507 1995 11 23 Mw is the moment magnitude, taken from the Harvard CMT catalogue. %d-c shows how well the CMT solution is represented by a double-couple source (i. e. slip on a planar fault). This number, expressed as a percentage, is obtainedfrom the relative sizes of the eigenvalues of the moment tensor, and is 100% for a pure double-couple source and 0%for a compensated linear vector dipole (the largest departure from a fault-like' source. It gives some idea of the 'quality' of the CMT solution.

A B C D

Earthquake Hazard in Lebanon

37s

32*

33*

15 34*

35*

36*

•« ^^

^

37'

38' 37*

'iioRT "

> fU.V

36"

38*

35'

35*

c if

34s

34s

Falm>nd«s

i

33*

33^ \

e

32*

32'

' BARCi

31*

3V

30s

^

Site/

C

29* 32/

33*

30s

34s

35*

30mnVyr

-ft

36*

37*

38s

29*

Fig 3.3. Focal mechanisms are best-double-couple solutions from the Harvard CMT catalogue in the period 1977-1999. Earthquakes A-D are listed in Table 3.3. Small white circles are epicentres of earthquakes of mj, > 5.2 from the catalogue of Engdahl et al. (1998) for the period 1964-1998. Black circles are earthquakes of M s > 5.7 from 1900-2000. GPS velocity vectors relative to Eurasia are from McClusky et al. (2000). The Yammouneh fault is marked Y and the position of the Roum fault is marked R.

16

Elnashai and El Khouty

The Dead Sea transform fault system forms the plate boundary that links the Arabian plate convergence in southern Turkey with the active seafloor in the Red Sea. It extends for about 1,000 km from the Gulf of Aqaba in the south to a plate boundary triple junction in south-central Turkey. This system evolved since mid-Cenozoic time as a result of the break up of the Arabian plate from the African plate. As a result of along-strike variations in the orientation of this predominantly left-lateral fault system, important compressional (e.g. Mount Lebanon and Anti-Lebanon mountains) structures have developed since Miocene time along this plate boundary. The relative simplicity of the fault system in the southern segment between the Gulf of Aqaba and the pull-apart basin of the Galilee Sea and the Hula depression changes into a more complex system with major compressional structures and numerous "braided" strike-slip faults in Lebanon (e.g. Walley 1988). Locally along the fault zone, there are minor components of extension, compression, and up-warping. The Dead Sea, Lake Tiberias, and the Hula and Ghab depressions are a few manifestations of the "leaky" nature of this complex transform boundary. The Dead Sea rift system is widest and deepest at its southern end in the Gulf of Aqaba area. The Aqaba earthquake of 22 November 1995 was located in the central part of the Gulf of Aqaba along one such transform fault. From this point the fault system can be traced northwards. The basins along the Dead Sea rift are asymmetrical with steeper bounding faults on the eastern margin. As the fault system continues northwards through Lebanon and southwestern Syria, it follows a prominent restraining bend. Within this bend, the relatively simple fault trace branches off into several splays including the prominent Yammouneh fault crossing the Mt. Lebanon ranges on the western side of the Bekaa Valley. The Serghaya fault branches from the main transform near Lake Tiberias and can be traced north-eastwards for at least 150 km traversing the Anti-Lebanon ranges and the eastern side of the Bekaa Valley of Lebanon. The Rachaya

Earthquake Hazard in Lebanon

17

and Roum faults also splay within a large restraining bend. The Roum fault in Southern Lebanon, the seaward splay off the southern Dead Sea fault, may represent the extinct northward extension of the Miocene Dead Sea fault (Chaimov etal. 1900). Primary among these faults are: (1)

(2) (3)

The Yammouneh fault, which is clearly observed beneath the Bekaa valley between the Lebanon and Anti-Lebanon ranges, Figures 3.3, 3.4a, and 3.4band, The Roum fault in south Lebanon, and The Serghaya fault in southwest Syria.

The Yammouneh fault represents the main northward continuation of the Dead Sea fault system and merges with the Ghab fault in northwestern Syria (e.g. Quennell 1958, 1984, Feund 1965, Beydoun 1977). The N-S trending Ghab fault itself merges into a complex "braided" fault system near the border between Syria and Turkey that strikes in a NE-SW orientation and in turn merges with the major East Anatolian transform fault system in southern Turkey (e.g. McKenzie 1976, Dewey etal. 1986).

18

Fig 3.4a. Laedsat photo of area under investigation

Elnashai and El Khoury

Earthquake Hazard in Lebanon

19

Though geological evidence supports an estimated 100 to 110 km of displacement along the southern segment of the Dead Sea fault system since mid-Cenozoic time, a much lesser amount of displacement is observed along the "braided" faults in Lebanon and Syria. Most of these faults, moreover, have not yet been carefully studied, especially with regard to their Quaternay displacements.

20

Elnashai and El Kfmury

Fig 3.4b. Landsat photo of area under investigation. The arrows point to the Yammouneh fault in the Bekaa valley.

Earthquake Hazard in Lebanon

3.2

21

Historical Seismicity

Historical seismicity suggests that the above faults are capable of generating large earthquakes, thus posing a significant seismic hazard. The most recent large earthquake along the northern Dead Sea fault system occurred on 25 November 1759 within the large restraining bend that contains the Bekaa valley, with an estimated magnitude in excess of 7.0. Below, a full account of the most damaging historical earthquakes in Lebanon is given. 303 Apr 2 A severe earthquake shook Sidon and Tyre, and Caesarea, where it seems to have caused a sea-wave, but no damage. It also may have affected Byblus. Many buildings collapsed, which killed thousands of people. 455 Sept A violent earthquake in Tripolis on the Lebanese coast. The city was very badly damaged and may even have been destroyed. In particular all public buildings of the city together with the aqueduct fell down, but were all rebuilt by the Emperor Marcian. This earthquake may have caused destruction over a much wider area of the Lebanese littoral. 476 Sept A violent earthquake destroyed the town of Gabala (m.Jablah). The emperor gave gold for reconstruction. 551 July 9 A large earthquake along the Dead Sea Fault zone was felt as far north as Laodicea and Antioch, where it caused slight damage, and as far south as Alexandria where it caused panic, and reportedly eastward as far as Mesopotamia. It generated a seismic sea-wave off the Lebanese coast: the sea first retreated for about a mile (1.6 km) before returning as a colossal wave which flooded and partly flattened Tyre, Sidon, Berytus, Tripolis, Botrys and Byblus (Jubail), Entaradus (Arwad), Sarepta, and Trieris between Botrys and Tripolis, at al-Heri, in the bay of Shekka, Enfe, on the coast 20 km SW of Tripolis, or Shamarra.

22

Elnashai and El Khoury

Beirut seems to have been the worst hit: it was badly damaged by the earthquake and sea-wave, but most of the destruction seems to have resulted from the ensuing fire which apparently raged for two months. Beautiful buildings and works of art were lost. The famous Law School, one of only three in the Roman Empire, was destroyed and had to be temporarily transferred to Sidon (which cannot therefore have been badly damaged) during reconstruction. 30,000 people were known to have been killed in Beirut: the high death toll is not surprising, as there were many students at the Law School, and also many people were drowned by the sea wave, as when the sea had retreated they had gone down to the sea-bed to plunder sunken wrecks. At the coastal town of Botrys, just north of Byblus, part of the Libanus Mountain, known as the Lithoprosopon or "Face of Stone", broke off and fell into the sea. This was actually a great benefit to Botrys, because it thereby acquired a sheltered harbour in which large ships could dock. Further up the coast Trieris, the exact location of which is not certain, was also destroyed. There was widespread destruction in Syria, where it said that 101 towns/villages fell, and there were fissures in the ground: the earthquake may have been felt as far as Jerusalem, and it is likely that Caesarea and Pella were damaged, and Gush Halav, 30 km SE of Tyre, seems to have been destroyed. Funds for the reconstruction of the more important cities were provided from the imperial treasury: Beirut was partially rebuilt so that it was recognisable, but was apparently much changed. 847 Nov 24 A violent earthquake at dawn destroyed many houses and bridges in Damascus, including the el-Aamer mosque throwing down a quarter of it with its minaret. The earthquake was at least felt in al-Ghutah, it destroyed Darayyah, al-Mazza, Beit Lihyah and other places, and was felt as far away as Antioch. The earthquake continued until at least midday, and caused great fear, the people praying in the mazallah while it lasted. 991 Apr 5 A strong earthquake during the night in Damascus and the surrounding region caused 1000 houses to collapse on their inhabitants in the

Earthquake Hazard in Lebanon

23

city and in the region as far as Baalbek (Heliopolis), resulting in great loss of life. The village of Duma sunk into the ground, indicating either faulting or a landslide. Aftershocks followed for almost a month, one being recorded for May 2nd, and another for May 5th, and caused additional damage, so the population left Damascus and camped in the countryside. 1033 Dec 5 A violent earthquake occurred in Palestine just before sunset, and was felt in Egypt and Syria. The epicentre seems to have been around Ramla: a third of its houses were destroyed together with half of its wall, and although many of the people who were in the town at the time were killed, most of the male population at least were spared, because they were working out in the fields. The earthquake caused panic, and the survivors evacuated the town, joining the farm workers outside the city for eight days during the destructive aftershocks, one of which may have brought the mosque down. In Jerusalem there was widespread damage: parts of the Dome of the Rock, the mosque of David, and the mosque of Abraham in Hebron, collapsed, shocks continuing to be felt for two days. Nearby Jericho and Arriha were heavily damaged. At Nablus (Neapolis/Shechem) on the coast, 300 people died when the houses collapsed, and the nearby village of Badan was swallowed up in the ground with many others. Acre (Ptolemais) also collapsed. At least half of Banyas (Caesarea Philippi) fell down, and around Lake Tiberias the mountains were seen to move, trees were uprooted and wells overflowed. The earthquake was less strongly felt further south, although it still caused damage: the minaret of the great mosque in Ashqelon fell down, as did the pinnacle of the minaret of the mosque at Gaza. The earthquake was followed by a tsunami, probably off the coast of Acre. The sea flowed out several kilometres before flowing back as a tidal wave an hour later. Although it killed those who were foraging on the seabed, there is no evidence that it caused destruction inland. 1042 An earthquake occurred in Syria, affecting Ba'albek and Tadmur - the latter was heavily damaged, many of the inhabitants dying when their houses collapsed.

24

Elnashai and El Khoury

1063 Aug A destructive earthquake on the Syrian littoral. The walls of Tripoli fell down, and there was widespread destruction in Antioch (Antakia) Laodicea (Al-Ladhiqyyah), Tyre (Sur), Acre (Akko) and in many other cities in both Byzantine and Arab territory. Strong aftershocks followed for some days, possibly up to two weeks, destroying more buildings in Antioch, in particular the patriarchal church of St. Peter. 1157 Aug 12 The culmination of over a year of foreshocks, a violent earthquake occurred in Syria and along the northern section of the Dead Sea Fault: it was felt over an area of 3 million sq. km and killed many thousands of people. Because of the numerous fore- and aftershocks, it is difficult to date the event precisely, but it seems that the most violent shock was on Aug. 12. As a result of the massive destruction caused by this earthquake, the defences of several Muslim fortress-cities on the Frankish borders were heavily damaged, and it seems that the Franks took advantage of this. The Sultan, Nureddin, ordered tax relief so as to expedite repairs. The city of Hamah was the worst affected, where almost all the inhabitants were killed by the collapse of the citadel and most of the houses. Hamah is not recorded as having received any tax-relief, presumably because it was of no military importance. We know that repairs were made, however, because when Hamah was damaged again by the earthquake of Oct.30, according to one source "the [structures which had been] rebuilt were destroyed again". At nearby Shaizar (Caesarea) the damage was equally heavy: a mountain outside the town split in two, causing the castle that was built on it to collapse. This castle was the seat of the local ruling family, who were feasting there at the time; all of them except a woman and her slave died. The town was probably not so badly damaged, but as it was of strategic

Earthquake Hazard in Lebanon

25

importance and its main defence had been destroyed, Nureddin granted it a year's tax relief equal to 2.7 kg of gold. Kafr-Tab suffered almost total destruction and very few of its inhabitants escaped. Ma'arra an-Numan also suffered destruction, and the ground may have broken open, swallowing up some of the inhabitants. It received = 8.2 kg of gold in tax relief. At Afamya (Apamea), built on the edge of a plateau, the earthquake caused a landslide, which tipped the fortress into a lake, which resulted in many deaths. Hims/Homs (Emessa) suffered the destruction of most of its buildings, but the death toll was low as the population fled during the foreshocks. It received tax relief of = 71 kg of gold. Salamiyya, 25 miles NE of Hims, was also damaged severely by this earthquake but is not recorded as having received tax relief, presumably because it was not a fortress-town. At Aleppo the damage was less serious: most of the inhabitants left during the foreshocks and only about 100 were killed. Some of the towers of the fortifications collapsed together with many houses. Relief was = 136 kg of gold; Damascus was given = 55 kg of gold in tax relief. Tell Harran, a small village near Aleppo, suffered severe damage and was given relief of = 13.6 kg gold. 'Azaz and Tell Bashir, important frontier fort-towns, also suffered damage, and were given relief of = 27.2 kg and = 57.2 kg of gold respectively. Hisn al-Akrad and " Arqa, in Frankish territory, were badly damaged, and in Latakia (Laodicea) everything except the church fell down. The ground split open, revealing ancient ruins, and it is probable that liquefaction occurred.

26

Elnashai and El Khoury

Probably less serious damage was sustained in Antioch, and also further south in Jabala (Gabala), Jubail (Byblus), Tripolis, Sur (Tyre), 'Akko (Acre), Saida (Sidon) and Beirut. The earthquake had damaging effects as far down as Rahba/Rehabot (al-Mayadin) on the Euphrates. 1170 Jun 29 Preceded by foreshocks, an earthquake occurred early in the morning, continuing for some hours, on the northern part of the Dead Sea Fault (Figure 3.5). It was as destructive as that of 1157 Aug. 12, but the epicentral area on this occasion was Aleppo, which was very heavily damaged: many public buildings, houses and the city walls collapsed, leaving it defenceless. Destruction was not total however, as the Syrian church survived, and the Ulu Cami mosque survived with damage to its minaret, the crescent of which was hurled almost 200 m. Even so, the death count was very high, estimates ranging from 5000 to 80 000: part of the reason for this is that Aleppo's jails were crowded with Christian prisoners. In addition there was faulting and the ground liquefied, causing a flow of black water which drowned many of the injured who were trapped in the ruins. Further deaths also resulted from the pollution of the water by corpses.

Earthquake Hazard in Lebanon

27

Fig 3.5. Historical earthquakes in the Levant after Ambraseys and Barazangi (1989). Note that date, location and magnitudes of some events have bee revised, listed in Table 5.1 and shown In Figure 7.3.

Antioch was also hit: the wall on the bank of the River Orontes collapsed, along with some houses. The Greek church collapsed, but the church of St.

28

Elnashai and El Khoury

Peter suffered the destruction only of its sanctuary, where the clergy were celebrating the liturgy at the time, and so were killed along with some of the congregation. In addition the ground opened, although the cracks later closed up. The death toll was relatively low, about 50, most of whom were probably in the church of St. Peter, thus it is unlikely that Antioch was severely damaged; in fact the earthquake seems to have caused more fear than anything else, reportedly prompting the city's rulers to expel the Greek patriarch (who may have been fatally injured in the earthquake) and to restore the Frankish bishop Amalric. There are records of structural collapse in the coastal towns of Latakia (Laodicea), Jabalah, Baniyas (Caesarea Philippi/Valence), Tripolis, Tyre and Acre: oddly Beirut, between Tripolis and Tyre, is not mentioned. In Tripolis a very large number of buildings were destroyed, including the cathedral, with many casualties ensuing; the defences of Tyre were badly damaged, and the fortress of Hunain, ca.32 km from Baniyas may have collapsed. Destruction was by no means universal in any of these cities, however, as certain churches are reported as having withstood the shock in Jabalah and Laodicea. All these towns were in Frankish territory, many of the Frankish inhabitants probably never having experienced an earthquake before, and as a result of this they lived in craven fear for some time afterwards, this being exacerbated by the aftershocks. In the north, Samosata, nearly 200 km from Aleppo, suffered damage to its walls. Edessa, however, was unscathed, although vertical and horizontal ground motions were very strongly felt there until around 3 pm, to the extent that the clergy in the nearby church of St. Anania clung to the altar but could not stand still. Further south, the walls of Baghras, some 18 km north of Antioch, fell, and the citadel of Harim, nearer to the latter city, was badly damaged. Walls and houses were collapsed in Shaizar, Hamah and Hims (Emessa), and the Frankish citadels of Hisn al-Akrad, Arqa (ar-Raqa) and Safitha were damaged, although Hisn probably not as badly as some sources claim; and at

Earthquake Hazard in Lebanon

29

Ashtera, ca.60 km SE of Safita, there is no record of any damage. The defences of the Muslim border-town of Barin were destroyed, and the Frankish castle of Qusayr was damaged, the altar of its church falling down. At Ba'albek the earthquake caused considerable damage to houses and defences; in the mountains above the town, deep cracks appeared in the mountains. At least part of Damascus collapsed, and the crenulations and part of the roof of the mosque came down. Apparently only one man died there, however, as most of the population fled when they felt the foreshocks. The earthquake nevertheless affected a huge area, being felt in Mosul, Sinjar, Nisibis (Nusaybin), Basra, Baghdad and Wasit, and possibly in Armenia. It is not certain whether Jerusalem and Palestine were damaged or not, but the earthquake was probably felt there, and it is likely that any damage would have been slight. Estimates as to the duration of aftershocks vary from a fortnight to four months, which would tend to indicate variation from place to place. In all, an estimated thirty towns and villages were significantly damaged by this earthquake, leaving both the Franks and Muslims open to military attacks from each other: ironically, this resulted in a period of unofficial truce, as both sides set to repairing as quickly as possible the fortifications of border citadels. The Muslim Atabeg Nureddin toured Syria, inspecting the damage at Ba'albek and Hims, where he left garrisons to carry out the necessary works. Travelling via Barin and Hamat Nureddin came to Aleppo, where the scale of the destruction reportedly so appalled him that he camped outside the city and supervised the repairs to the fortifications and the principal mosques himself. Wood was used extensively in the rebuilding work, which demonstrates that its earthquake-resistant properties were appreciated: the cost was partially offset by tax-relief on timber.

30

Elnashai and El Khouty

By contrast Antioch, although not so badly affected, seems to have suffered from a shortage of funds as, according to a source writing about ten years later, the repairs did not reach "even a mediocre standard". 1202 May 20 A large, destructive earthquake occurred in the Middle East around daybreak on 20 May 1202, being felt from Lesser Armenia, parts of Anatolia and NW Iran to Qus in upper Egypt, and from Constantinople to Iraq and Mesopotamia, an area of average radius ca.1200 km (Figure 3.5). Extensive and serious damage was caused in Syria: in Tyre, everything except three towers and some outlying fortifications was destroyed. Probably a third of Acre was destroyed, with considerable damage to the royal palace and the walls, although the Knights Templar complex in the SW of the city was spared. At least some repairs were effected to both cities. Inland, in Samaria (Shamrin) and Hauran, damage was equally severe: it was reported that Safa was partially destroyed, with the deaths of all but the son of the garrison commander, and also Hunin (Chastel Neuf), Baniyas (Paneas) and Tibnin (Toron). Bait Jann was "swallowed up" with its walls. A village near Busra was reportedly razed by a landslide. Nablus was totally destroyed, except for a few walls, and may have suffered further damage in an aftershock: this region must be near the epicentral area. Most of the towns of the Hauran were so badly damaged as to be not readily identifiable. Jerusalem suffered relatively lightly, but further north Damascus was strongly shaken: apparently many houses collapsed and major buildings near the citadel were damaged. The Ummayad mosque lost its eastern minaret and 16 crenellations on its north wall, one man died when the Jirun (eastern) gate fell; the lead dome split in two and one other minaret fissured. The adjacent Kallasa mosque was ruined, killing two people, and the nearby Nureddin Hospital was completely destroyed. People fled to the open spaces. Further north, houses collapsed in Jubail (Gibelet), the walls of Beirut had to be repaired and Batun was damaged, but this damage may have been due at

Earthquake Hazard in Lebanon

31

least partly to military attacks. Rockfalls on Mt. Lebanon killed 200 people; nearby Ba'albek was destroyed. The extent of damage to Tripoli was probably heavy, as there was great loss of life. The castles of Arches fArqa) and Arsum ("Arima?) were destroyed, and Chastel Blanc (Safitha) was badly weakened; the castles of Margat (Marqab), Krak (Hisn al-Akrad) and Barin were damaged but still secure. Tarsus (Tortosa) largely escaped damage, however. At Hims (Homs, Emessa) the earthquake threw down a watchtower of the castle. In Hamah there were two shocks, the first lasting an hour (probably rapid shocks in succession), then a second, stronger shock, destroying the castle and many houses and other buildings. The earthquake was felt in Aleppo and other regional capitals, and less strongly in Antioch, in Mosul and Mesopotamia, as far as Iraq, Azarbaijan, Armenia, parts of Anatolia and the town of Akhlat. In Egypt the shock was felt from Qus to Alexandria: three violent shocks in Cairo woke sleepers and shook buildings, risking the collapse of tall structures. In Cyprus the earthquake was strongly felt, and a seismic sea-wave between the island and the Syrian coast flooded eastern parts of Cyprus: there may have been damage to structures. The death-toll is uncertain as the earthquake coincided with famine and plague, but it must have been high, being at daybreak when most people were still in bed. Aftershocks lasting at least four days were reported from Hamah, Damascus and Cairo. (Ambraseys and Melville 1988) 1354 Oct 28 Hims, Hamah and Ba'albek were shaken by an earthquake, which brought a number of walls down. The worst casualties were in Hamah, Hims and Ba'albek where people were killed.

32

Elnashai and El Khoury

1404 Feb 20 An earthquake occurred in the region west of Aleppo, destroying many places. The earthquake was followed by aftershocks, some of which were not felt in Aleppo: these may have lasted until June and caused considerable concern. Many buildings were destroyed in Tripoli, and either as a result of this shock or of its aftershocks part of the castle of Marqab collapsed in mid-March, together with other buildings elsewhere (Figure 3.6). 1408 Dec 29 The earthquake sequence which began in 1403 culminated in a destructive event which affected the northern part of the Dead Sea Fault as far as its junction with the southeast Anatolian fault, and an area running at least 100 km WNW along the latter. The worst destruction appears to have been at Shughr, ca.50 km south of Antioch, which was razed with its castle and district, and apparently there were only 50 survivors. There was heavy damage in Aleppo, Tripoli, Latakia, Jibla, where 15 people reportedly died, and Balatanus, where the castle collapsed and 15 people are said to have died under the debris. A fault-break occurred for ca.20 km south from Qusair (m. Qal'at al-Zau), and the earthquake may also have triggered a landslide at Saltuham, south of Qusair, although this is not certain. It is also possible that Saltuham was in the Jebel Akra area and that in fact the faulting extended out SW under the sea, or that submarine slumping occurred. Note that the strands of the Dead Sea fault system which run discontinuously along the west flank of the Orontes towards Jisr al-Shughr have been quiescent for more than 200 years. The earthquake is also reported to have caused destruction in Cyprus, and to have had some effect on its mountains and watering places. It is also probable that a tsunami occurred between there and the Syrian coast: the sea withdrew a long way then flowed back again, but did not cause any damage (Ambraseys and Melville 1995).

Earthquake Hazard in Lebanon

33

1759 Oct 30 This earthquake affected the region of Safad and a mountain area to the northeast where many villages were destroyed with the loss of about 2,000 lives (Figure 3.6). Safad and Qunaitra were almost totally ruined, and many of the inhabitants were killed, while others left the towns. Damage extended to Saida, where a few houses collapsed, as well as to Saasaa, Nazareth and Acre where private and public buildings were ruined, but without casualties. In Damascus and in the plain of Ghutah, the shock caused considerable concern and widespread minor damage; one or two houses collapsed. Many public buildings, particularly minarets, were damaged. Further away, in Tiberias damage was widespread. The shock was felt at Antioch, Aleppo, Jerusalem and Gaza and it was reported by sailing boats off Cyprus. A seismic sea-wave flooded Acre and the docks at Tripoli, causing no damage. (Ambraseys and Barazangi 1989) 1759 Nov 25 This was a major shock which lasted 50 sec. and almost totally destroyed all villages in a narrow zone extending to the north-east for about 120 km along the Litani and Bekaa valleys into the upper reaches of the Orontes river in southwest Syria (Figure 3.6).

34

Elnashai and El Khoury

.Antioch

aAlappO

— 36 .Ladhikiya

\

(Shaizar

,VI

I I

.Hama

\

.Hisn alAkrad i Horns

/

30li •Tripoli

\

I

,

as B81 b ak

vm^? i

" ' '

^Beirut •Ssrghaya fsaida •Zebedani / , /% /'Doumair S Damascus ,

/

—34

liCassarea .Nablus SJaffa"

32

Aerusalsm

0

h

34 I

36

Fig 3.6. Intensity distribution of the earthquake of 1759

100 —»— km

200

—I

38 i

Earthquake Hazard in Lebanon

35

The epicentral region of this earthquake comprised the meizoseismal area of the foreshock of 30 October, where the destruction was cumulative. Figure 3.6 shows the intensity distribution of the event. Safed, rebuilt after the first shock, was totally destroyed. The settlements to the north were razed to the ground, and those in Bshara and in the Shouf region suffered likewise, including monasteries and cloisters. Destruction was equally heavy in the upper reaches of the Barada river at Serghaya and Hasbaya, and Ba'albek was totally destroyed with great loss of life. The stream that supplied water to Ba'albek was dammed up. Heavy damage extended to Ras Ba'albek. As a result of the earthquake, a series of ground ruptures many yards wide were formed running continuously along the Bekaa valley, to the north of Baalbeck as far as opposite Reipoli, and to the southwest to the plain of Satern, a total distance of about 100 km, probably the surface break of the Yammouneh fault. The shock was felt throughout Anatolia up to 1,100 km away and in Egypt. The number of people killed in this earthquake is estimated at 40,000 [Ambraseys and Barazangi 1989]. 1796 Apr 26 A destructive earthquake in the Sahel district of Lattakiya on the Syrian littoral. The shock almost totally destroyed the coastal plain between Jeble and Bucak where most of the houses collapsed. Destruction extended to villages in the Nahr al-Kebir plain an area about 40 km long and 15 km wide. In Lattakiya, 1500 out of a population of 5,000 were killed and one third of the town collapsed. The shock was felt at Saida, 230 km away [Ambraseys 1989]. 1837 Jan 1 The earthquake occurred on 1 January 1837 at about four in the afternoon and lasted about 20 seconds. It was probably a multiple event, the second shock occurring about five minutes after the main shock. Destruction or heavy damage was done along a relatively narrow zone which extended from the coastal area of Saida (Sidon) through the inland iklimi

36

Elnashai and El Khoury

(regions) of al-Touffa, Marjuyum, Bshara to Lake Tiberias, for a total length of about 120 km. Damage in the epicentral region was widespread and varied from place to place over short distances. Much of it can be attributed to the high vulnerability of the local type of houses and also to the siting of villages, particularly those in the central and north part of the affected area A general observation about a typical rural house in Syria and Palestine in the early 1800s is that its inherent strength was very low and extremely variable, and its vulnerability to earthquakes high. Local houses were chiefly one-storey high, of rubble masonry construction covered with heavy flat roofs, already in a ruinous state. The degree of damage or destruction caused by an earthquake was usually proportional to the size of the housing conglomerate or village; the larger the conglomerate, the heavier the apparent damage. The high vulnerability of local houses becomes apparent when we consider the relatively small damage sustained by the few properly built public structures in the epicentral region, such as convents, churches, walls and bridges, as compared to ordinary dwellings. Another factor that contributed to the erratic distribution of damage in this and other earthquakes before and after 1837 (Ambraseys, 1997) in this region, is site effects. Many villages, for defence reasons, were built on hilltops or on steep slopes, overlooking their fields. Many of these sites have had already suffered from slides and regional instability of the ground, particularly those built on marls, chalk and weathered limestone. The destruction of Safed, for instance, and of the nearby villages of Ein Zeitim, Reina and Jish in the earthquake of 1837 can be attributed to the instability of their sites rather than to the exceptional severity of the shock. Regarding the loss of life, the earthquake happened in the evening, during a wet period in winter when most people were indoors having dinner, which contributed to the relatively large number of casualties. Figure 3.7 summarizes the near-field effects of the earthquake. With the exception of the epicentral region shown in this figure, to the west of it the Mediterranean Sea and to the east a sparsely populated tribal area provided no macroseismic information. The shock was felt within a radius of about

Earthquake Hazard in Lebanon

37

500 km and at large distances it caused long-period effects, such as slow and sustained oscillations of the ground and nausea, common far-field characteristics of large earthquakes. In the near-field the assessment of intensity is complicated owing not only to the high vulnerability of local dwellings and site effects mentioned earlier but also due to the possibility that the reported macroseismic effects and damage are due to two successive, relatively large magnitude, events. A double shock, with separate epicentres, would have affected significantly the observed distribution of damage in the epicentral area but it would have little effect on the distribution of intensity at large distances. The available macroseismic data do suggest sub-events but it is not possible to say which parts of the zone were associated with them.

38

Elnashai and El Khoury

Fig 3.7. Intensity distribution of the earthquake of 1837. Full, dotted and open squares show intensities VIII, VII and VI respectively. Star shows the location of the earthquakes of 26 March 1997 at 04h 22m and 13h 20m, of M w = 5.1 and 4.9 respectively.

Earthquake Hazard in Lebanon

39

Maximum damage was experienced along the Roum fault and its small branches which occupy the regions of Marjuyum and Bshara to the southwest. There is no conclusive field evidence that this earthquake was associated with surface faulting (Ambraseys, 1997). 1956 Mar 16 (19:32:30 Ms 4.84) A damaging foreshock in the southwestern Lebanon range. In Shihim 11 people were killed and caused serious damage at Katermaya, Jun, and Mukelle. It was followed by the main shock 20 minutes later. 1956 Mar 16 (19:42:22 Ms 5.06) An earthquake in the southwestern part of the Lebanon range. Its epicentral region is located on the west facing slopes of the range which extends between the Mediterranean coast in the west and the Burak river on the east. In the north-south direction the area is confined by the al-Dammour and Zahrani rivers. Damage was widespread centring in the lower reaches of the Bisri river, 70 km south of Beirut, and it was confined between the villages of Ghaziye, Katermaya, Shihim, Mukhtara, Beter, Kfar Hune and Kfar Bait, within a radius of about 12 km. The affected area is relatively densely inhabited, consisting chiefly of small settlements of adobe or dry stone masonry houses built on sloping ground, where about 6,000 dwellings collapsed or were damaged. In the larger villages such as Shihim, 200 houses damaged by the foreshock fell in the main shock, 200 more were damaged, killing 22 people and injuring 60. At Jun most of the houses fell and the church was ruined with the loss of four lives. At Rum half of the 300 houses and the church as well as those in the near-by settlement of Azur collapsed or were damaged beyond repair. Near here, in Qeitule all 100 houses and the church were ruined with the loss of four lives. In Jezzin most houses suffered different degrees of damage and two people were injured. The convent was shattered but the statue of the Virgin was left intact.

40

Elnashai and El Khoury

In all, 122 people were killed in 33 settlements and villages. The shock triggered slides, rock-falls and damaged retaining walls of mountain roads. Outside this region damage decreased rapidly with distance concentrating on vulnerable sites. In Beirut the shock was felt, at a few places causing some minor damage and the evacuation of 13 old houses. The earthquake was felt as far north as Baniyas, in Damascus, Amman, in northern Israel and in south-east Cyprus, within a radius of 170 km. 3.3

Estimates of Rates

The simple image of the active tectonics of the eastern Mediterranean described in Section 3.1 above was first proposed by McKenzie (1970) and has now been confirmed directly by GPS measurements (Figure 3.1 and McClusky et al. 2000). A lot is also now known about the rates of these various processes, based on both global plate models and GPS measurements. GPS measurements show the slip rates across the North Anatolian and East Anatolian fault zones to be 24 ± 1 and 9 ± lmm/yr respectively. Central Turkey has been shown to be rigid with internal deformation of less than 2 mm/yr, and its westward motion is well described by an anticlockwise rotation about an Euler pole in the Nile delta (McClusky et al. 2000). Based on the distribution of earthquakes and limited GPS measurements in Cyprus, the southern boundary of the rigid central Turkey block follows a line from Rhodes along the south Turkish coast and Florence Rise, south of Cyprus, and then to the Gulf of Iskenderun (Figure 3.1). The northward motion of Africa relative to Eurasia is described by a rotation pole near the Canary Islands, and is about 10 mm/yr at the longitude of Lebanon. Arabia moves northward faster than this because its motion is enhanced by sea floor spreading in the Red Sea. It is this effect that causes the left-lateral strike-slip motion on the Dead Sea fault system, which extends from the Gulf of Aqaba in the south to SE Turkey in the north (Garfunkel et al. 1981). The spreading rates and directions in the Red Sea and the effect of any slow opening in the Gulf of Suez are not well determined, and consequently both the Africa-Arabia and Arabia-Eurasia plate motions are relatively uncertain. The most popular global plate model, called NUVEL-1A

Earthquake Hazard in Lebanon

41

(DeMets et al. 1994), and its predecessors, provide an unsatisfactory fit to the sea-floor data in the Gulf of Aden and Red Sea and also suggest far more convergence across the Dead Sea fault zone than is likely. As a result, several other plate models that specifically address this region and which are based on re-interpretations of the sea-floor, earthquake and fault data have been proposed (Joffe and Garfunkel 1987; Le Pichon and Gaulier 1988; Jestin et al. 1994). All of them predict about 8 to 10 mm/yr of nearly N-S left-lateral slip across the Dead Sea fault zone as a whole. Our somewhat uncertain knowledge of the Arabia-Africa and Arabia-Eurasia motions has not yet been improved by direct GPS observations. GPS sites do exist on the Arabian plate, and some are shown in Figure 3.1 but they are all close to active fault systems (either the suture zone in eastern Turkey or the Dead Sea fault zone) and their apparent motions may have been affected by elastic strain accumulation near those faults. Sites have now been installed within the stable interior of Arabia, and after a few years the motion of Arabia within the global plate framework will be much better known. A few GPS sites in the Levant are worth a closer look (Figure 3.3). In the south, the sites at TELA, BARG and KATZ straddle the Dead Sea Fault Zone, and might be thought to provide direct evidence of its slip rate, Table 3.2. The sites at TELA and BARG, west of the fault zone, do indeed move north (relative to Eurasia) slower than KATZ to the east, reflecting the expected left-lateral motion. However, these sites have only been occupied twice over quite short periods, so the errors in the velocities may be relatively large. TELA, which is away from the main trace of the Dead Sea fault zone, has roughly the expected velocity of the African plate, which is encouraging. However BARG and KATZ, which are within the deforming zone itself rather than on stable blocks to the side, have velocities that may be affected by elastic strain accumulation. These measurements cannot be used with confidence to refine the motion across the Dead Sea fault zone, and 8 to 10 mm/yr from the 'global' models remains the most likely estimate.

42

Elnashai and El Khoury

The three GPS stations at DORT, ULUC and SENK in the north of Figure 3.3 are also important, as they occur in a complicated area where the Arabia-Africa, Turkey-Arabia and Turkey-Africa boundaries are all expected to meet. In this region, as is typical on continents; the deformation is complicated and distributed over many faults rather than confined to simple 'plate boundaries' (Lyberis et al. 1992). Nonetheless, as McClusky et al. (2000) point out, stations ULUC and DORT show motions similar to those expected for stations on the stable central Turkey block, while the velocity of station SENK is consistent with the motion of the African plate (see also Figure 3.1). Once again, some caution must be applied here, as the stations have only been occupied twice over relatively short periods. However, if this interpretation by McClusky et al. (2000) is correct, it implies that the Turkey-Africa boundary (running south of Cyprus) comes on land between ULUC and SENK, and that SENK is on the African plate. This would require significant left-lateral slip on the northern part of the Dead Sea fault zone, in contrast to the interpretation of Butler et al. (1997, 1998), who suggest that the Africa-Arabia boundary follows the Roum fault offshore south of Beirut. In summary, the best estimate of the likely slip rate across the Dead Sea fault zone is about 8 to 10 mm/yr of approximately N-S left-lateral motion, extending from the Gulf of Aqaba to Antakya (Antioch). From the earthquake distribution and known patterns of active faulting, this motion is likely to be confined to a relatively narrow zone perhaps < 100 km wide, but may spread out more than this in restraining bends such as those associated with the Yammouneh fault and the Palmyrides (McBride et al. 1990, Ch&\mo\ et al. 1990, 1992, Butler et al. 1998). 3.4

Twentieth Century Seismicity of the Levant and Lebanon

There exist a considerable number of parametric and annotated earthquake catalogues for the area: Sieberg (1932), Kallner-Amiran (1951-52), Arieh (1967), Ben-Menahem (1979), Plassard and Kagoj (1981), Arieh et al. (1985), and Ben-Menahem (1991), to which we may add the regional and global catalogues often used in hazard assessment: Gutenberg and Richter

Earthquake Hazard in Lebanon

43

(1954), Karnik (1968), Amiran et al. (1990), Rothe (1989) and Arad et al. (1998). A few of these catalogues are pertinent, quoting their sources, some are out of date or compiled at second hand containing many inaccuracies, and some are oversimplified and misleading, containing gross errors and duplications in entries which are occasionally difficult to disentangle. It is only during the last two decades that cataloguing of recent earthquakes have become more systematic and reliable. Seismicity, hazard and risk have been examined by Ben-Menahem et al. (1982), Ben-Menahem et al. (1976), Kovach et al. (1986), Striem (1986,) Kovach (1988), al-Tarazi (1992); Yucemen (1992), Salamon (1993) and Harajli(1994). Locally, with the exception of the last two decades, seismographic monitoring was poor with only one seismographic station originally operating in Beirut and then in Ksara since 1911, and later with another two vertical variablereluctance seismographs installed at Jerusalem and Safed in 1954. The operation of the latter instrument, which was transferred to Haifa in 1959, was frequently interrupted until 1963. The only other near stations are at Helwan and Athens. Seismological bulletins are available from Ksara [Annales de l'Observatoire de Ksara (1926-30), Bulletin Seismique, Observatoire de Ksara (1911, 19131969)] as well as the Seismological Bulletins of the Seismological Division of the Institute for Petroleum Research and Geophysics of Israel from September 1981 onwards. The examination of this material showed that much of what is available for the assessment of hazard in Lebanon in the form of parametric catalogues is derivative of earlier works with no recourse to original information. For events prior to the mid 1970s no reappraisal of locations or uniform estimation of magnitudes has been attempted. One feels therefore that much effort is being diverted to using elaborate statistical methods for the

44

Elnashai and El Khoury

evaluation of seismic hazard on guessed input parameters and that more data from observations are now required. The present study supersedes these catalogues for events in the region and no attempt is made to draw attention systematically to previous misconceptions, although individual inaccuracies are discussed as seems relevant or important. Instrumental data for the early period come from station bulletins world-wide, reporting phase data and ground amplitudes as well as from bulletins of regional networks such as: Notizie sui Terremoti Aweniti in Italia 1897-1915, published by the R. Ufficio Centrale di Meteorologia e Geodinamica in Rome; Reports, Seismological Investigations 1895-1915, Circulars 18991913 sad Bulletins 1913-1915 published by the Seismological Committee of the British Association for the Advancement of Science; Bulletin de la Commission Centrale Seismologique Permanente 1902-1908 and 1911-1913; Monatsberichte 1899-1906 and Wochentlicher Erdbeben-Bericht 1905-1915 der Kaiserlichen Hauptstation fur Erdbebenforshung in Strassburg, as well as Gutenberg's unpublished work-sheets and station bulletins. For the recording capabilities of these early stations in the region see Ambraseys and Finkel (1987), material which is indispensable for the study of the seismicity of the first three decades of this century. Instrumental epicentres for earthquakes in the first half of the period investigated are very approximate, and they must be used with caution. For the early part of this period BAAS (1912, 1913) published a considerable number of epicentres of the larger shocks for some of which it seems macroseismic information was used but not quoted, to determine the approximate position and time of the event, whenever it was possible. When local observations were not available, as is the case with most of the earthquakes offshore and in remote parts of the region, epicentres are likely to be in error. Macroseismic epicentres are also an approximate indication of the location of an earthquake. For large events such locations are adequate for the

Earthquake Hazard in Lebanon

45

determination of their magnitude or for their association with local tectonics, considering that earthquakes of M s > 6.0 will have ruptured faults many kilometres in length, in which case the definition of epicentre loses its practical meaning. Figure 3.8 shows the distribution of all instrumentally determined epicentres in the Middle East, most of them of small magnitude, during the last 30 years. Table 11.2 lists 242 earthquakes in the period 1900-1998 retrieved and reappraised in this study area. Epicentres are flagged according to the method used to estimate their position: 0:

1: 2: 3: 4: 7: 8:

(08%) Epicentres reported chiefly by Beirut/Ksara for which we could find no data to improve their position or to assess their magnitude. (04%) Locations calculated by ISS/ISC. (21 %) Positions "adopted" by ISS/ISC without calculation, which we found difficult to improve. (20%) Macroseismic locations for events for which information is adequate. (07%) Teleseismic locations calculated for this study using standard ISC procedures for events with sufficient P readings. (39%) Locations recalculated by Engdahl et al. (1998) (01%) Epicentres given by BCIS Strasbourg.

The most widely accepted measure of earthquake size is magnitude, derived from instrumental measurements. Many different types of magnitude have been developed, depending on the type of instrument used and parameter measured, serving different purposes. The local or Richter magnitude ML was designed for the classification of local shocks in Southern California in the late 1930. It is based on the maximum sample energy at periods less than 1 second, and distances not greater than 600 km. It saturates at relatively small values and it requires calibration to regional conditions. The body wave magnitude Mb is also a measure of the short period radiation of body waves and may be used at larger distances than ML. However, it saturates at low

46

Elnashai and El Khouty

magnitudes and is of little use for engineering purposes. Of the various magnitude scales currently in use the main one, for the study of tectonics and seismic hazard from historical data is the surface-wave magnitude Ms, expressed as moment magnitude M for comparison with modern events. Before proceeding further it is important to review briefly the development of the surface-wave magnitude M s and moment magnitude M and the reader is referred to Appendix Al. Misuse of these earthquake parameters often results in serious errors in the assessment of hazard and design groundmotions.

Earthquake Hazard in Lebanon 35°

47 40°E

Fig 3.8. Regional seismicity 1970 - 1991. Note that north western Syria is temporarily quiescent, probably due to the high seismic activity of the region during the 11' to the 14' centuries

Surface wave magnitudes have been calculated for 128 earthquakes using two different methods, flagged by: 0:

for 41 earthquakes of the period before 1960, Ms was computed using the number of station that recorded the event (e.g. Ambraseys 2000).

48

1:

Elnashai and El Khoury

These earthquakes are too small (3.0 Ms < 4.1) for surface-wave amplitudes to be reported in station bulletins. for 88 earthquakes M s was calculated uniformly using the modified Prague formula and the method described in Appendix Al.

Seismic moments for 127 earthquakes come from two different procedures flagged as: 0: 1:

for 115 events for which M0 is calculated from equations (Al -12) and from the appropriate value of MS; and for 12 events for which we have CMT values.

Moment magnitude M has been calculated in the standard way from equation (Al-7). On the same table we show the values of surface-wave magnitudes reported by different authors: Mk by Karnik (1996), Mp by Plassard and Kagoj (1981), Mb by Ben-Menahem (1979) and by Ma by Arieh et al. (1985). Short-period body-wave magnitudes nib reported by ISC are also shown in the last column. The seismicity of the region around Lebanon 1970-1991 is shown in Figure 3.8.

Chapter 4

Magnitude Recurrence in Lebanon and Adjacent Regions

Lebanon occupies a small area comprised between 33° and 34°N and 35° to 36°E and seismic activity there during the 20th century has been very low. During the 20th century there have been 60 earthquakes in this area but only 13 of them reached a magnitude Ms > 4.0, Table 4.1. The total amount of seismic moment release in the last 100 years is trivial and only 1.3xl025 d.cm, which is equivalent to a single earthquake of about M s = 5.8. The largest 20th century event in Lebanon is the Rum earthquake of 16 March 1956. Its surface wave magnitude did not exceed 5.1 but together with its almost equally large foreshock ten minutes earlier of M s 4.9, it did considerable damage to local vulnerable houses. The macroseismic effects of this event are summarized in earlier sections of this report. Table 4.1: 20th Century earthquakes in Lebanon (33° to 34°N and 35° to 36°E) Y

M

D

OT

1907 1907 1910 1911 1913 1921 1921 1925 1926 1928 1930

6 6 7 7 11 4 4 3 10 2 1

10 1210 22 1532 10 1924 0 13 19 1324 20 1604 21 800 16 630 11 429 9 2022 13 240

N°

E°

h

33.7 33.7 34.0 33.8 34.0

35.5 35.5 36.0 35.4 35.8 35.4 35.5 36.2 36.5 35.9 35.8

0 0 0 0 0 0 0 0 0 0 0

34 33 33.4 33.3 34.1 33.8

49

Ms 4 4.3 4.63

0 4.3 5.38

0 0 0 0 0

logM 0 23.24 23.54 23.87

0 23.54 24.62

0 0 0 0 0

Mw 4.76 4.96 5.18

0 4.96 5.68

0 0 0 0 0

mb

50

Y 1930 1930 1930 1930 1937 1940 1942 1944 1945 1947 1949 1950 1951 1952 1954 1954 1954 1955 1956 1956 1957 1957 1957 1958 1958 1959 1959 1959 1959 1959 1959 1959 1960 1960 1960

Elnashai and El Khoury

M 3 6 9 11 9 12 9 4 10 4 10 3 8 11 1 4 11 12 3 3 2 5 7 10 11 4 4 4 5 7 10 11 1 3 4

D 25 14 14 18 13 9 28 24 24 3 28 1 5 18 26 1 8 27 16 16 2 14 29 1 5 10 11 19 21 12 7 29 28 21 22

OT 1858 1932

223 1312

850 2036

117 1824 1738 1431 1910 2130 1512 1905

246 1727

324 201 1932 1942

33 25 119 933 2046 1323

754 214 237 1326 1514 2048 1936 1902 2227

N°

E°

h

33.8 34.3 34.8 34.4 34.5 34.8 34.4 33.8 33.9

35.8 36.5 36.6 36.6 36.7 36.3 36.6 35.8 36.2 36.7 35.5 35.5 36.1 36.2 36.4 36.1

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

34 33 33 34.1 34.2 33.9 33.7 34.3 33.7 33.6 33.6 33.6 33.8 34.6 33.8 34.5 33.4 33.4 33.4

33 33 33.8 33.6

33

36 36.3 35.4 35.5 35.4 35.9 36.8 35.9 36.5 35.6 35.6 35.5 35.5 35.5 35.8

35

33.5

35.5 35.6

34

36

Ms

0 0 4.5 0 0 0 0 0 0 0 0 0 4.33

0 0 0 0 0 4.84 5.06

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

logM 0

0 0 23.70

0 0 0 0 0 0 0 0 0 23.57

0 0 0 0 0 24.08 24.3

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Mw

mb

0 0 5.1 0 0 0 0 0 0 0 0 0 4.98

0 0 0 0 0 5.32 5.47

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Earthquake Hazard in Lebanon

Y 1960 1961 1962 1965 1965 1968 1971 1971 1972 1983 1992 1997 1997 1997

M 8 10 2 5 8 3 4 11 2 6 3 3 3 10

D OT 28 223 11 354 1 932 2 1151 24 124 26 1937 16 2127 8 1755 8 551 3 204 9 1954 26 422 26 1320 30 1734

51

N°

E°

h

33

35.4

34.3 33.5 33.5 33.8 34.1 33.7 33.3 33.9 33.8 34.4 33.4 33.7 34.9

35 35

0 0 0 0 0 25 15 0 0 2 4 10 3 15

35.3

35 35.5 35.5 35.5 36.2 35.8 35.9 35.4 35.5 35.1

Ms 0 0 0 0 0 0 0 0 0 4.31 3.95 4.64 4.83

0

logM0

0 0 0 0 0 0 0 0 0 23.55 23.19 23.88 24.07

0

Mw 0 0 0 0 0 0 0 0 0

mb

4.8 4.5

4.97 4.73 5.19 5.32

4.6 4.1

0

4.2

It is important to note here the grossly inflated magnitudes assigned to these two events of 5.5 and 5.8 by Plassar and Kagoj (1981), 6.1 by BenMenahem (1979) and 5.3 and 6.0 by Arieh et al. (1985), used by other authors to assess hazard in Lebanon. Table 4.2 presents the data used to calculate M s from the standard Prague formula with station corrections for the Rum earthquakes. The data in Table 11.2 permit the assessment of the reliability of Ms estimates in different parametric catalogues, which are important in the selection of input data for hazard analyses. Figure 4.1 shows a comparison between Ms estimates calculated in this study and by Karnik. For M s > 5 the two estimates are very similar. However, we cannot say the same for Plassard and Kagoj's Mp estimates; as Figure 4.2 shows Mp is systematically inflated by 0.5 magnitude units, and occasionally by one whole unit. Figures 3.8 and 4.1 show clearly the large overestimation of magnitude Mb by Ben-Menahem and Maby Arieh. It is unlikely that a reliable hazard analysis can be performed with such large dispersion in magnitude.

52

Elnashai and El Khoury

Table 4.2: Calculations example of M s for the Rum earthquake (from stations, e.g. BEO, HUR, etc..) 1956 Mar 16 19h 32m 30s 33.60°N 35.40°E Stat. Ti At T2 A2 D° M s St.Cor BEO 12.0 1.9 0.0 0.0 06.2 4.61 .30 HUR 12.0 3.0 0.0 0.0 19.2 4.93 -.02 STR 15.0 4.0 0.0 0.0 25.5 5.16 -.26 UPP 21.0 1.9 16.0 1.2 28.6 4.80 .10 KIR 21.0 2.5 16.0 1.0 35.2 5.03 -.12 Foreshock Magnitude 4.91(± 0.19) 1956 Mar 16 19h 42m 22s 33.60°N 35.50°E Stat. Ti Ai T2 A2 D° M s St.Cor BEO 13.0 7.0 0.0 0.0 16.2 5.14 -.03 HUR 12.0 3.0 0.0 0.0 19.2 4.93 .18 STR 16.0 6.0 0.0 0.0 25.4 5.31 -.20 UPP 21.0 3.8 21.0 3.1 28.6 5.09.02 ABE 17.0 3.0 0 .0 0.0 24.6 4.96 .15 CRT 10.0 2.0 0.0 0.0 31.9 5.20 -.09 KIR 20.0 2.8 17.0 2.1 35.1 5.14 -.03 Event Magnitude 5.11(± 0.12)

Earthquake Hazard in Lebanon

53

Fig 4.1. Comparison of recalculated surface-wave magnitudes M s in this study with surfacewave magnitudes Mk calculated by Karnik (1996)

Fig 4.2. Comparison of recalculated surface-wave magnitudes Ms in this study with surfacewave magnitudes Mp calculated by Plassard and Kagoi (1981)

Elnashai and El Khoury

54

6.5-

•

S y i

3.5-

S

3.5

S

S /

•

'

S

4

5

4.5

6

5.5

6.5

Ms Fig 4.3. Comparison of recalculated surface-wave magnitudes Ms in this study with surfacewave magnitudes Mb reported by Ben-Menahem (1979) 6.5

•

•

5.5

i

• ' • ••

^ ^ y

>

4.5

^ 3.5 3.5

4.5

5

5.5

6

6.5

Ms Fig 4.4. Comparison of recalculated surface-wave magnitudes Ms in this study with surfacewave magnitudes Ma reported by Arieh et al. (1985)

We examined the seismicity of the whole Levantine zone, the activity of which is summarised in Table 11.2. Figure 4.5 shows the cumulative frequency-Ms distribution of earthquakes during 100 years in the larger study area. The overall "rate" coefficient in terms of surface-wave

Earthquake Hazard in Lebanon

55

magnitude is b = 0.77, which is sensible. Figure 4.6 shows a similar plot but with moment magnitude as the variable. The rate coefficient now is 1.0. These two figures show that depending on whether a hazard analysis is based on attenuation laws that are a function of M s or of moment magnitude M, it will be necessary to use different frequency-magnitude distributions. 2.5-

•

i>

•

• •

5IS

•

o

i

• •

0-

•

1

3.5

4.5

5

5.5

6.5

•

»i

7.5

Ms Fig 4.5. Cumulative frequency-magnitude distribution for the Levant for the period 19001998 in terms of Ms

56

Elnashai and El Khowy Z.&-

•

1

1

• •

• • II

•

o> o

•

•

" • •

0-

3

3.5

4

4.5

5

5.5

6

6.5

•

7

1

7.5

Mw Fig 4.6. Cumulative frequency-magnitude distribution for the Levant for the period 19001998 in terms of Mw

There are several features in the present dataset that would seem to require special discussion regarding completeness of the 20th century dataset. The most obvious is perhaps the remarkable quiescence of seismic activity during the 20th century along the whole zone. This feature shows up very clearly when presented in histogram form (Figure 4.7) of cumulative moment release in the Levant. It is clear, therefore, that the seismicity of the 20th century is not a useful guide to the long-term earthquake activity in the Levant fault zone that includes Lebanon. The activity of the last 100 years has been far lower than is necessary to account for the Arabia-Africa motion, yet in previous centuries large earthquakes are known to have occurred (Jackson and McKenzie 1988; Ambraseys and Melville 1988; Ambraseys and Barazangi 1989; Ambraseys 1997).

Earthquake Hazard in Lebanon

57

9.00E-KJ1 8.00E+01

1

7.00E+01

J-

6.00E+01 3 5.00E+01 CO O 4.00E+01 3.00E+01 2.00E+01 1.00E+01

T

r

—I

**

- —

tw

0.00E+00 1 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Year Fig 4.7. Cumulative seismic moment distribution with time for the Levant. M0 in d.cm

Figure 3.3 shows the best-double-couple Centroid Moment Tensor (CMT) solutions from the Harvard catalogue for the period 1977-1999. A number of strike-slip focal mechanisms near SW Cyprus attest to activity on the Cyprus arc, including one in 1996 of Ms 6.8. NW of Cyprus some earthquakes have depths as great as about 150 km, associated with the slow subduction of the Mediterranean Sea floor beneath the Florence Rise (Jackson and McKenzie 1984), but otherwise everywhere in Figure 3.2 earthquake focal depths are expected to be less than about 15 km. Around the Gulf of Iskenderun the available mechanisms show the NE-SW left-lateral motion associated with the East Anatolian fault system (such as the earthquake of Mw 6.2 near Mersin on 27 June 1998) and also some extension, which is expected between Turkey and Africa in this area (Jackson & McKenzie 1984). Some scattered activity occurs offshore between Lebanon and Cyprus, with a number of poorly-located events of M s > 5.7 before 1963, but also one (marked C in Figure 3.3 and Table 3.3) in 1993 that is better-located. A focal mechanism is available from the CMT catalogue for this 1993 event,

58

Elnashai and El Khoury

but it is poorly determined (Table 3.3), probably because it was quite small (Mw 5.4). Little is known of the geological structures offshore that accommodate the Africa-Turkey motion between Cyprus and the Gulf of Iskenderun. The largest earthquake between Aqaba and Antakya in the last 100 years was one in Jordan of M s 6.1 on 11 July 1927, assumed to be associated with the Dead Sea fault (Avni 1999). Only three focal mechanisms are available from the 1977-1999 CMT catalogue (A, B and D in Figure 3.3 and Table 3.3) and they are all small (Ms < 5.7). Events A and D show the expected left-lateral motion parallel to the Dead Sea fault zone (D was an aftershock of the large 1995 earthquake of Mw 7.2 in the Gulf of Aqaba), and are apparently good solutions (Table 3.3). Event B (Mw 5.3) occurred west of the Dead Sea fault with a focal mechanism showing nodal planes striking NE-SW and NW-SE rather than N-S. It was located in a region of complicated conjugate strike-slip faulting west of the Sea of Galilee (Ron et al. 1984), and is a useful reminder that not all earthquakes in the region occur on the main structure.

Chapter 5

Synthesis of Seismicity and Rate Information

Historical seismicity shows that large earthquakes have occurred in the past in the Lebanese section of the Dead Sea fault zone. It is probable that at least two of these, in 1202 and 1759, occurred on the straight Yammouneh fault segment of the main left-lateral fault system itself (Ambraseys and Melville 1988; Ambraseys and Barazangi 1989), which runs NNE-SSW for about 150~km and is thus oblique to the overall Africa-Arabia motion. It is therefore not surprising that in this area the deformation is probably distributed over more than one fault, and may even be separated into its strike-slip and thrust components, as is seen elsewhere in regions of oblique convergence such as central California (e.g. Mount and Suppe 1987). A manifestation of this distributed deformation may be the large (M - 7) earthquake of 1837 in southern Lebanon, which appears not to have occurred on the Yammouneh fault, and may have been on the Roum fault instead (see Section 3.2 and Ambraseys, 1997).

Table 5.1: Large earthquakes in the Levant 1000 - 2000

Y

M

D

N°

OT

E°

M

32.4 35.5 7.1 1033 12 1800 05 35.5 36.5 7.4 1157 08 12 0000 1170 06 0700 36.0 36.5 7.3 29 1202 05 0600 34.0 36.0 7.3 20 12 0000 36.0 36.0 7.2 1408 29 33.5 36.0 7.2 1759 11 25 0000 33.5 35.5 7.1 1837 01 01 1600 1995 11 22 0415 28.8 34.8 7.1 Epicentres are only indicative of the general epicentral area. Magnitudes, derived from macroseismic data, have been adjusted to account for the cumulative effects caused by the large magnitude aftershocks that followed all the events.

59

60

Elnashai and El Khoury

It is evident from the quiescence of the 20th century compared with the large earthquakes of historical times that the main Dead Sea fault system itself remains locked between slip events in major earthquakes. We can at least combine some of this historical knowledge with our understanding of present-day overall slip rates and earthquake mechanics to obtain some idea of how frequently the large earthquakes are to be expected. In common with all major continental strike-slip faults, the Dead Sea fault system is likely to be segmented, with rupture in individual earthquakes limited in length by structural discontinuities or bends. The available historical data suggest that both the 1202 and 1759 earthquakes ruptured the Yammouneh fault over a distance of about 100 km, which is most of its length between the more N-S trending segments of the fault system to the north and south. In most large interplate earthquakes the ratio between average displacement and fault length is between 2 and 5 x 10"5 (Scholz et al. 1986), so we would expect these earthquakes to have produced slip of 2 to 5 m in each event. Slip of this amount on a fault rupture 100 km long extending to 15 km depth yields an estimated seismic moment of between 0.9 and 2.3 x 1027 d.cm, equivalent to a magnitude Mw of 7.2-7.5. If slip accumulates on the locked fault at a rate of ~10 mm/yr (the total Africa-Arabia motion), we would expect the average recurrence time of such earthquakes to be 200 - 500 years. Over the 300 km length of the northern part of the Dead Sea Fault system we would expect, on average, one such earthquake about every 100 years, which is in reasonable agreement with the historical evidence (Ambraseys and Barazangi 1989). The question now arises of how complete is the 20th century record for the Levantine zone and for Lebanon. In particular Table 5.land Section 3.2 (historical seismicity) clearly show that this zone has been inactive in recent year as compared to earlier periods and because of this any analyses must be necessarily rather approximate, and do not warrant great sophistication. Indeed too sophisticated a method carries with it the danger that its weaknesses and assumptions may not be appreciated. Conversely, a simple method may be discredited just because it exposes the underlying problems too clearly. As a first approximation, combining the data in Table 5.1 and

Earthquake Hazard in Lebanon

61

Table 11.2 for M s > 4.0, we may estimate the annual frequency-magnitude distribution for the Levant, which is shown in Fig 5.1. For M s < 7.2 and for M s

log(N0) = 3.0 - 0.73MS > 7.2

(1)

log(N0) = 14.8 - 2.37MS (2)

Equation (1) is representative of 20th century activity and predicts an earthquake somewhere in the Levant zone of magnitude 7.0 every 130 years. Equation (2) is for larger earthquakes and is based on historical data only. It is far less well constrained and predicts a major earthquake of 7.5 every 950 years, which is plausible. However, in trying to detect the reason for the bi-linearity of the distribution, there is one difficulty, which is often overlooked. It is that the same dataset is used both to select the feature (bilinearity) to be tested and to carry out the test. This does not include the possibility of clustering (non-independence) of successive events on significant level that is likely to be present in the seismicity of the Levant.

Elnashai and El Khoury

62

0.5 0 -0.5

f-

15

s^A

-2.5

\B

-3 -3.5 4.5

5.5

6

6.5

7.5

Ms Fig 5.1. Cumulative, annual frequency-magnitude distribution for the Levant over the period 1000 to 2000. No is the annual number of events of magnitude equal to or greater than M s . A:log(N0) =3.02-0.72Ms B:log(N0)=14.8-2.37Ms

Frequency assessments such as equations (1) and (2) are inherently very approximate and several factors could change these figures. The straightness of the Yammouneh fault segment suggests that it is pure strike-slip in character and that it does not accommodate the necessary shortening component required by its orientation: this component will be taken up on nearby thrusts that will also pose seismic hazard that is difficult to assess. In addition, not all the strike-slip component maybe restricted to the Yammouneh fault, and other adjacent or nearby faults, such as the Roum fault, may also be active. Finally, other fault segments could be longer, moving in less frequent but larger earthquakes.

Chapter 6

Selection of Attenuation Relationship

6.1

Peak Ground Acceleration (PGA)

In the literature, there are many attenuation relationships in terms of peak ground accelerations, derived for different parts of the world. Table 6.1 gives a selected list, which are considered applicable for Lebanon. There is no regional attenuation relationship derived for Lebanon. In fact, there are no known strong motion records produced in Lebanon. Data from Syria is not available either. The Joyner and Boore (1981) relationship is very commonly used but this relationship is mainly derived with Californian data and uses Mw as the measure of earthquake size. The Gitterman et al. (1994) relationship is derived from very few Israeli data, and the accelerations were mainly derived from seismogram records. This relationship is based on MLThe European attenuation relationships are based on datasets that contain records from Middle Eastern counties including Turkey, Israel, Armenia and Iran. There are several attenuation relationships using European data, Ambraseys and Bommer (1991), Ambraseys (1995b), Ambraseys et al. (1996). Of these, the third relationship is preferable (see Figure 6.1), since it was derived after checking the peak accelerations from digital records, over and above the merit common to the three of using uniformly assessed magnitude Ms and distance parameters. Ambraseys et al. (1996) also include attenuation relationships in terms of the acceleration response spectra. The PGA attenuation relationship was checked against the reported values in the Aqaba region due to the strong earthquake of magnitude Ms=7.06 on 22 November 1995 in the Gulf of Aqaba. Osman & Ghobarah (1995) report peak strong motion acceleration of 0.09g and 0.1 Og in Eilat and Aqaba. These agree very well with the computed value of 0.1 g for the earthquake at a distance of 40km, which is the estimated separation of the

63

Elnashai and El Khoury

64

recording sites from the end of the fault rupture associated with this earthquake. 0.8 r" •

Attenuation Relationship Ambraseys et al (1995)

0.7

-•*.. 0.6 0.5 'So ¥ O

Ms

'" * -.

5.0

\ _ _

0.4

P.

V

\

v

0.3

5 5

6.0 ---6.5

\

v

\

0.2 0.1 1

0

1

1

1

L.

•

1

1

1

—

i

i

1—•

r T T i ' i 7 J j a ' J " T ' . , . ' . i . ua

..«-if—i.

i i i i i

1000

10 100 Nearest Distance, d (km)

Fig 6.1. Mean attenuation of peak ground accelerations (PGAg ) with distance (d^,,) for Ms = 6.5, 6, 5.5 and 5. (Ambraseys et al. 1996)

Attenuation relationships of ground motions are of the form: l°g (y) = Ci + c2M - c3 log r - c4r +aP

(3)

where y is the ground motion parameter in consideration, Ci>2,3,4 are constants determined for the ground motion parameter, rr is the standard deviation representing the scatter of data in the attenuation relationship and P is a parameter which takes the value of 0 when the predicted value represents the mean and P equals one when the predicted value represents the mean plus one standard deviation. V is a distance parameter, usually of the form r = V(d2 + ho2). For example, Ambraseys et al. (1996) give: log (PGAg) = -1.39 + 0.266 M5 - 0.922 log r + 0.25P

(4)

Earthquake Hazard in Lebanon

where

65

r = V(d2 + 3.52) d = nearest distance of the site from the fault (km)

Table 6.1: Coefficients of attenuation relationships of the form of Equation (3). Reference Joyner&Boore(1981) Ambraseys & Bommer (1991) Ambraseys (1995b) Ambraseys et al. (1996) Gitterman et al. (1994)

c2M 0.249MW 0.238MS

c3 1.0 1.0

c4 0.00255 0.00050

K

-1.02 -1.09

7.3 6.0

0.26 0.28

-1.43 -1.39 -5.026

0.245MS 0.266MS 0.989 ML

0.786 0.922 1.0

0.0010 0.0 0.0043

2.7 3.5 2.7

0.24 0.25

Cl

-

Ambraseys et al. (1996) also give an attenuation relationship including the effect of site conditions: log (PGAg) = -1.48 + 0.266MS - 0.922 r + 0.117SA + 0.124SS + 0.25P (5) SA and Ss are dichotomous parameters that take the values of 0 or 1 only depending on the site conditions. For rock sites, both SA and Ss are zero, while for stiff soil sites, SA =1 and Ss=0 and for soft soil sites, SA=0 and S.=l. Note that the constant Ci for rock sites is slightly smaller than that given by the general equation (4). For stiff soil sites, the equivalent constant becomes very nearly equal to the general equation while for soft soil sites, the value is slightly higher. Therefore the results of hazard analysis will change accordingly. The site-specific equations (5) are used in this study for determining hazard at specific sites, while the general equation (4) is be used for producing hazard maps.

Elnashai and El Khoury

66

6.2

Peak Ground Displacements (PGD)

The attenuation of peak ground displacement has not been adequately addressed by researchers in the past. The reason for this is the difficulty of obtaining reasonable peak ground displacements from double integration of strong motion acceleration records. Morevoer, traditional code design did not require explicit determination of displacements. Bommer and Elnashai (1999) give a well-verified relationship (Figure 6.2) in the form of: log (PGDcm) = -1.757 + 0.526 Ms - 1.135 log r + 0.114SA + 0.217 Ss + 0.32 P (6) where r = V(d2 + 3.52) 12 Attenuation Relationship Bommer & Elnashai (1999)

10 •

Q O a.

Ms — 5.0 -5.5 •--6.0 •—6.5

6

10

100

1000

Nearest Distance, d (km) Fig 6.2. Mean attenuation of peak ground displacements (PGDcm) with distance (dim,) for Ms = 6.5, 6, 5.5, 5. (Bommer and Elnashai, 1999)

SA and Ss are defined in the same way as in Equation (5).

Earthquake Hazard in Lebanon

67

Hazard maps of PGD for Lebanon are given in Appendix A3 for rock site condition only. Ground displacements and displacement spectra are increasingly being employed for seismic assessment and design, hence the effort to include such values here for future development of seismic codes in Lebanon in line with modern approaches of using displacements as the primary design parameters in stead of accelerations, and noting that the former exhibits stronger correlation with damage than the latter. 6.3

Acceleration Response Spectra (SA)

Ambraseys et al. (1996) present a list of the attenuation parameters for spectral accelerations at 5% damping in a tabular form for various periods from 0.1 to 2.0 seconds, using an equation of the same form as Equation (5) for PGA. These equations are based on regressions on a dataset of over 420 strong-motion accelerograms from Europe and the Middle East, and they have been very widely adopted for use throughout these regions.

6.4

Displacement Response Spectra (SD)

Bommer et al. (1998) give similar relationships to those of Ambraseys et al. (1996) for spectral displacements instead of accelerations. The equations are presented for various periods up to 4.0 seconds (although the authors state that only those up to 3.0 seconds can be used with confidence) and damping levels from 5% to 30% of critical. In this only the 5% damped spectral ordinates are used. Higher damping values are more relevant to direct displacement-based design of structures, a subject under current active development. The development of direct displacement-based design tools for Lebanon is beyond the scope of this study. These relationships for SD are based on regressions on a dataset that is comprised of the records from the dataset of Ambraseys et al. (1996) from earthquakes of Ms 5.5 and greater, supplemented by a few additional records from recent earthquakes and removing weaker motion. It should be

68

Elnashai and El Khoury

noted that in a strict sense these equations are only applicable for earthquakes of Ms 5.5 and above, but it is assumed herein that they can also be applied to smaller events without significant error.

Chapter 7

Source Zone Modelling and Recurrence Relationship

7.1

Completeness Test

The seismicity data in Table 11.2 is first checked for completeness by using the method of Stepp (1971). The method is described in a simple manner in the Appendix A2.

1 r

Completeness Test: Stepp Method

° 6.0 ± 0.25

• X

• 5.5 + 0.25 D

0.1

* 5.0 ± 0.25 x 4.5 ± 0.25 • 4.0 ±0.25

0.01 10 Time (years)

100

Fig 7.1. Plot of the duration of data and standard deviation for completeness test following Stepp (1971) method.

Figure 7.1 shows that the list can be considered to be complete for magnitudes 5.5+0.25 and 5+0.25 bands within the last 99 years. Magnitude 6±0.25 earthquakes are difficult to judge but are perhaps complete within

69

70

Elnashai and El Khoury

the last 20 years. Magnitude 4.5±0.25 and 4.0+0.25 may be considered as complete in the last 20 years and again with the whole 99 years data. There are very few data points available for magnitudes below this level. For large magnitude earthquakes, there is not enough data to test the theory. In developing the recurrence relations, earthquakes of magnitude 4 and above will be considered. 7.2

Source Zone Modelling

From the map of the epicentres, Figure 7.3, derived from Table 11.2, between 27° to 37° N and 34° to 37° E, it can be clearly seen that the epicentres follow the general alignment of the Dead Sea Rift zone from the Gulf of Aqaba northward, along the Yammouneh and associated faults to the East Anatolian Fault Zone. However, it is difficult to attribute these epicentres to any particular faults in the region. Particularly within Lebanon, the epicentres are dispersed, earthquakes occurring on several minor faults branching off the dominant Yammouneh Fault. The Dead Sea Rift is about 20 km wide and in some places much more. Earthquakes tend to occur more in the boundaries of this zone. Above 36°N, the Yammouneh fault tends to merge with the East Anatolian fault zone. Figure 7.2 plots a close up view of faults in Lebanon. The Roum fault is of particular concern since it branches towards Beirut. It is to be noted that this fault is less than 50 km in length. An Ms=7 earthquake breaks about 45km along a fault (Ambraseys and Jackson 1998). From the map of epicentres, Figure 7.3, it is clear that there are two possible zones of seismic activity. The first one is linked to the Rift zone and its extension to the North toward Turkey. We assume that this zone terminates at 35°N. The reason for this limitation is the absence of earthquakes between the 35° and 36°N in the last century and the deletion of this area from the source zone results in high seismic activity within the source. A result of this omission will be to reduce the hazard to the north of 35° but this does not affect Lebanon and hence it is safely conservative for the purposes of this study. The second zone is linked to the East Anatolian Fault zone. A third zone is assumed, which is the Yammouneh fault within

Earthquake Hazard in Lebanon

71

the Rift zone. It is here that the large historic earthquakes (Ms>7) are assumed to occur as a result of the activity along the Dead Sea Rift extending from Gulf of Aqaba to the border of Turkey, from 28.5°N to 36°N. This gives a length of fault of 850km. However, within the last 1000 years, except for the Aqaba earthquake of 22nd November 1995, all other events occurred above the latitude 32°N. Taking this factor into account, the activity of the fault for the large earthquakes is considered above this latitude only. This assumption makes the fault more active for Lebanon. It is possible that for the next millennium this section of the fault may become less active, but consideration of high activity is conservative. The epicentres of the historical earthquakes do not exactly line up along the fault. This may be due to the inaccuracies of the determination of the historical epicentres or due to the fact that these earthquakes have genuinely been associated with other faults. The Rift itself is about 20km wide but the Yammouneh fault within Lebanon appears to be a linear structure. Fig 7.4 plots the earthquake epicentres and the seismic sources considered in the seismic hazard study.

72

Elnashai and El Khoury

MEDITERRANEAN

mm Fig 7.2. Plot of major fault structures in Lebanon. Note that Roum fault branches towards Beirut.

Earthquake Hazard in Lebanon

73

Fig 7.3. Plot of the epicentres of earthquakes from 1900-1998 within 27°-37°N and 34°37°E. The open circles represent the historical large magnitude, Ms=7+ earthquakes in the last 1000 years.

The area of the Dead Sea Rift Zone = 80301 km2 The area of the East Anatolian Fault Zone= 56550 km2 The length of Yarnmouneh fault = 450 km.

74

Elnashai and El Khoury

34

37

Fig 7.4. Plot of earthquake epicentres and the seismic sources considered in the seismic hazard study

In the first part of the report, the activities of the three source zones are put together and this gives recurrence relationship for the region, equations (1) and (2), as:

Earthquake Hazard in Lebanon

75

log (N) = 3.02 - 0.72MS ; 4.0 < M < 7.14

(7)

log (N) = 14.8 -2.37 Ms ; M >7.14

(8)

and

where N is the number of earthquakes of magnitudes greater than or equal to Ms per year over the whole area. 7.3

Dead Sea Rift Zone

If we consider the activities of the Dead Sea Rift zone alone and remove the aftershocks of the 22nd November 1995 earthquake, the recurrence relation (Fig 7.5) becomes: log (N) = 3.15-0.83MS

(9)

hi deriving the above recurrence relation, the Ms =7.06 earthquake of 22nd November 1995 is not included; this event stands alone in the figure. This clearly implies that 99 years data is not sufficient to derive the recurrence relationship of such large earthquakes. The recurrence relation implies that an Ms T earthquake has a return period of about 450 years, which is commensurate with the historical data. For the area source in the rift zone, the maximum earthquake will be considered to be Ms 7. This assumption covers the possibility of earthquakes in the Roum fault as well. The minimum magnitude is 4.

Elnashai and El Khoury

76

1 c

Rift Zone

0.1 ©

Z

0.01

Ms Fig 7.5. Recurrence relationship for the Dead Sea Rift Zone including Lebanon, the length covering from 27° to 35° N and the width covering the epicentres of earthquakes. In the Gulf of Aqaba region, the width is larger while in the middle section, the width is narrower and in the Lebanon and in the north it is wider again.

7.4

East Anatolian Fault Zone

Similarly, considering the earthquakes in the East Anatolian Fault Zone (Figure 7.6) the recurrence relation becomes: log(N) = 2.51-0.68Ms

(10)

In this region, no large magnitude (Ms>7) earthquake has occurred during the last 99 years. The catalogue of earthquakes of small magnitude (Ms <4.5) appears to be incomplete. It is assumed that the recurrence relation is valid between magnitudes 4 and 7 and that the maximum possible magnitude will be considered as Ms 7.

Earthquake Hazard in Lebanon

1 F

11

EAFZone

A

S 0.1

0.01

j

i

i

i

i

i

i

i

i

i

i

5 Ms Fig 7.6. Recurrence relationship for the East Anatolian Fault zone. This zone covers the earthquakes in the north of 36°N and also to the west of the Rift zone.

The recurrence relationships are further normalised by the source area, which yields: For Rift Zone: log («) = -1.75 - 0.83MS For EAF Zone: log («) = -2.24 - 0.68MS

(11) (12)

where n is the number of earthquakes of magnitudes > Ms per unit area (km ) per year. These two equations show that the EAF zone is less active than the Rift zone, and theirfe-valuesare appreciably different. The average of the two Z>-values agree with that given in equation (7).

78

Elnashai and El Khoury

7.5

Yammouneh Fault Zone

Of the large magnitude earthquakes, greater than 7.0, the Gulf of Aqaba earthquake of 1995 is the only earthquake which occurred south of latitude 32°N. All other historical earthquakes are between the latitudes 32° and 36°N. It is assumed that these earthquakes happened along the fault alignment mainly following the Yammouneh fault. The recurrence relation for these earthquakes, not including the 1995 Aqaba earthquake, Figure 7.7 is: log (N) = 17.48 -2.76MS

(13) Fault

u.ui

o

j

7

7.1

7.2

7.3

1

j

,

7.4

1

7.5

Ms Fig 7.7. Recurrence relationship for the Large magnitude earthquakes, Ms=7+ to the north of 32°N latitude. This relationship does not include the Aqaba earthquake of 22nd November 1995. It is assumed that these large earthquakes occur only on the Yammouneh Fault.

It is assumed that these earthquakes happened along a fault of total length 444 km (32°-36°), therefore the normalised recurrence relation becomes: log («!) = 14.87-2.76 Ms

(14)

Earthquake Hazard in Lebanon

79

where n\ are the numbers of earthquakes greater than or equal to Ms per annum per km length of fault. These large earthquakes are assumed to be independent of the smaller earthquakes in the Rift zone. Equation 14 shows a large V value. The usual value lies approximately between 0.5 and 1.5. This large V value merely proves the fact that the large magnitude earthquakes in a region do not usually follow the log-linear cumulative frequency distribution, Ambraseys & Sarma (1999). It is evident that this relationship for large earthquakes is different from the one mentioned in equation (8). This is because equation (8) is derived by assuming that the smaller and the larger earthquakes throughout the whole region are associated with the same tectonic processes and follow the same recurrence patterns. 7.6

Maximum Magnitudes

For both the Rift zone (Area Source) and the EAF zone, the upper bound magnitudes are set at 7.0 and the lower bound magnitudes are set at 4.0. The absence of magnitudes between 6 and 7 in the present century in the Rift zone is not sufficient reason to exclude the possibility of such events occurring. This particularly includes the activity of the Roum Fault. For the EAF zone, the maximum magnitude is set at 7.0 as well since there is no compelling reason to exclude the possibility of events up to this magnitude. For the activity of the fault the lower bound magnitude is set at 7.0 and the upper bound magnitude is set at 7.5, which is 0.1 higher than the largest historical earthquake. It is very unlikely that an earthquake of higher magnitude has been missed from an historical catalogue covering 1,000 years.

This page is intentionally left blank

Chapter 8

Hazard Maps

8.1

Peak Ground Accelerations (PGA)

Using the source zone characteristics described in the previous section and using the European attenuation relationship of Ambraseys et al. (1996) hazard at different grid points within Lebanon are computed by using the computer program EQRISK (McGuire 1976). The hazard is shown in the form of contour maps of PGA for return periods of 475, 1000 and 2500 years in Figures A3.1, A3.2, and A3.3. respectively. In order to determine the hazard probability of exceedance within a given time period can be calculated by using the following relationship:

where p is the probability of exceedance of a given ground motion within a given time, L = the time under consideration (design life of a structure, for example), and T = return period of the acceleration (years). The 475-year hazard map in terms of PGA shows relatively uniform levels of hazard throughout the Lebanon, with nearly all locations affected by values in the range 0.15g to 0.20g, the higher values reflecting the influence of the Yammouneh fault. The relatively small increase in hazard due to the Yammouneh fault compared to that at locations distant from this source, such as Beirut, confirm that the basic input parameters have been defined with an adequate level of conservatism. The 1,000-year and 2,500-year return period maps show an increasing influence of the infrequent but large magnitude events associated with the Yammouneh fault, such that for the longer return period the values of PGA along the fault zone are more than twice those in coastal locations such as Beirut and Tripoli. 81

82

8.2

Elnashai and El Khoury

Peak Ground Displacements (PGD)

Similar to the maps of PGA, hazard maps are prepared for peak ground displacements PGD and are shown in Figures A3.4, A3.5, and A3.6 for three return periods. These hazard maps show, as for the PGA maps discussed previously, relatively uniform hazard at the 475-year return period, but the influence of the large magnitude events on the Yammouneh fault results becomes more pronounced as the return period increases. Since PGD increases with magnitude more rapidly than PGA, all of the maps show greater increases in levels of ground motion with increasing return period that the PGA maps. For coastal sites, the value of PGA increases by about two-thirds from the 475-year to the 2,500-year return period, whereas for PGD the design values at these locations more than double. Along the Yammouneh fault, the values of PGD increase by almost a factor of five as the return period increases from 475 to 2,500 years. 8.3

Spectral Accelerations (SA) and Spectral Displacements (SD)

Spectral accelerations (SA) and spectral displacements (SD) for 5% damping at periods 0.1,0.3, 0.6, 1.2 and 2 seconds are computed for return periods of 475, 1000 and 2500 years. The results are shown as contours in Figure A3.1through A3.36. The figures display similar characteristics to those described for the PGA and PGD maps, in each case the parameters that are more sensitive to magnitude (i.e. those associated with longer response periods) increase more sharply for longer return periods. This observation is particularly important since it shows that if response spectra, whether of acceleration or displacement, are constructed by taking the ordinates from these maps rather than anchoring a constant spectral shape to the design value of PGA, a spectrum is obtained that can genuinely be described as being of uniform hazard.

Chapter 9

Site-Specific Hazard Assessments For the three most populated cities in Lebanon, site-specific seismic hazard assessments are carried out to obtain soil-dependent response spectra of acceleration and displacement. For each of the three cities, the hazard is assessed for return periods of 475, 1000 and 2500 years, and the resulting response spectra are presented for rock, stiff soil and soft soil sites. 9.1

City of Beirut

Beirut is located at 33°52' N and 35°30'E. Figure 9.1 and 9.2 show the probabilistic seismic hazard of Beirut in terms of SA and SD for 5% damping as a function of the site conditions and the return period. It can be noticed that at zero period, which represents the PGA, the values are marginally different from those shown in the maps. The reason for the difference is the use of equation (5) instead of equation (4) as explained earlier. It should be remembered, as noted previously, that the SD spectra are only considered reliable up to periods of 3.0 seconds.

83

84

Elnashai and El Khoury

Rock Stiff Soil Soft Soil

0.5

1 Period (Sec)

1.5

Rock Stiff Soil Soft Soil

0.5

1 Period (Sec)

1.5

Rock Stiff Soil

Fig 9.1. Uniform hazard acceleration spectra for Beirut for three site categories and three return periods

Earthquake Hazard in Lebanon

85

Rock Stiff Soil Soft Soil

^ .-.

/

/

.

^ ^ " " ^

T=475 Years

i

Period (Sec)

-Rock •Stiff Soil -Soft Soil

.,

f

, ' — ^.

T=1000 Years

Period (Sec)

: -

Rock Stiff Soil Soft Soil

_^.>* ^ — •-~--'"

s'--^Z7~-" ~-— ;

j^>—^^ p

f

^

.

T=2500 Years i

i

1

i

i

.

i

i

i

2 Period (Sec)

Fig 9.2. Uniform hazard displacement spectra for Beirut for three site categories and three return periods

86

Elnashai and El Khoury

An alternative probabilistic hazard assessment is performed for Beirut as a check. The method used may be classed as a "zone free" method. The basic difference between this method and that of Cornell (1968) incorporated in the EQRISK program is that the zone free method considers the random appearance of past ground motions at the site. Since past ground motions are related to past epicentres, there is a tacit assumption that occurrence of earthquakes are repeated at the past epicentres. This assumption is acceptable for small magnitude earthquakes and gives acceptable results. For large magnitude earthquakes, where only a limited number of events have taken place in the past, the randomness of these events cannot be accepted. Therefore, the results of the analysis tend to give higher values nearer to the past epicentres of large magnitude earthquakes and smaller values away from it. The program HAZAN (Makropoulos & Burton 1986) is used to compute hazard at Beirut and the results are shown in Figure 9.3 as a function of the return period. For 475 year return period, the PGA = 0.1 lg with the mean attenuation relationship and 0.19g for mean plus 1 standard deviation relationship. EQRISK gives PGA=0.16g. This implies that the seismic activity near Beirut is almost similar to the mean activity for the whole of the Rift region. 0.30

j= u u

0.20

< c

s©

o o.io

o.oo

HAZAN Mean + St. Dev. HAZAN Mean Values - - - -EQRISK i • • . . . . i .. i

• 0

1000

2000

3000

Return Period (years) Fig 9.3. Hazard curves for PGA in Beirut obtained using different probabilistic methods

Earthquake Hazard in Lebanon

9.2

87

City of Tripoli

City of Tripoli is located at (34°27'N, 35°50'E). Figures 9.4 and 9.5 show the probabilistic seismic hazard of Tripoli in terms of SA and SD, respectively, for 5% damping as a function of the site conditions and the return period.

Elnashai and El Khoury

Rock - -StiffSoil • -Soft Soil

Period (Sec)

Rock Stiff Soil Soft Soil

0.5

1 Period (Sec)

1.5

1 @

0.8

Rock - - - • Stiff Soil Soft Soil

•I fe 0.6

2 0.4

T=2500 Years 0.5

1.5 P e r i o d (Sec)

Fig 9.4. Uniform hazard acceleration spectra for Tripoli for three site categories and three return period

Earthquake Hazard in Lebanon

89

Period (sec)

Period (sec)

7

Rock - - - - Stiff Soil Soft Soil

.

' ^'**

,-£>-—~^~"

'

f

/ ,y

T=2500 Years

Period (sec) Fig 9.5. Uniform hazard displacement spectra for Tripoli for three site categories and three return periods

90

Elnashai and El Khoury

Using the zone-free method, the peak ground acceleration for this city for 475 year return period came to be 0.04g with the mean attenuation relationship and 0.08g for the mean-plus-one-standard deviation relationship which are considerably lower than that found by the CornellMvGuire method. The reason for this is the absence of earthquakes near Tripoli in the last century. 0.30

o.oo

r

r

0

1000

2000

3000

Return Period (Years) Fig 9.6 Hazard curves for PGA in Tripoli obtained using different probabilistic methods

9.3

CityofSidon

The city of Sidon is situated at (33°32'N, 35°22'E). Figures 9.7 and 9.8 show the site specific uniform hazard spectra of acceleration and displacement, respectively, and Figure 9.9 shows the comparison of PGA hazard curves obtained with both probabilistic approaches.

Earthquake Hazard in Lebanon

91

0.6

@ Hi

e o

eel

•-s « V

05 Rock - -Stiff Soil

04 0.3

s^

. .Soft Soil

.

u

<

a u

0?

-*J

IU

Q. C/3

01

• T=475 Years 0.5

0.6 •3

0.4

1 Period (sec)

1.5

Rock

-N.

- -Stiff Soil - -Soft Soil

0.2

T=1000 Years

a. 0

0.5

1 Period (sec)

1.5

1.2 Oil

tio

e

-Rock

1 0.8

•s u < •a J.

0.6

pec

a• -

0.2

_ . -Soft Soil

"..N.

0.4

t/i

. . .Stiff Soil

X\ T=2500 Years

0 0.5

1

1.5

Period (sec) Fig 9.7. Uniform hazard acceleration spectra for Sidon for three site categories and three return periods

92

Elnashai and El Khoury 14 Rock Stiff Soil Soft Soil

12

!'«

/ /—'

-

V Js~^~^

2

T= 475 Years

0

Period (sec) 20

Rock Stiff Soil Soft Soil

15

I

—

- • '

10

1/3

Period (sec) 30

(cm)

25

:

Rock Stiff Soil Soft Soil

,.>

20

•a

S 15 ; «t . 13 10 a c« 5

v"

S

V**»*"*

Jf'*/—

T=2500 Years

n Period (sec) Fig 9.8. Uniform hazard displacement spectra for Sidon for three site categories and three return periods

93

Earthquake Hazard in Lebanon

Using the zone-free method, the peak ground acceleration for this city for 475 year return period came to be 0.12g with the mean attenuation relationship and 0.2 lg for the mean plus 1 standard deviation relationship. EQRISK program using the Cornell method gives a value of 0.16g, Figure 9.9. The reason for this similarity between the two methods is that the average activity in the last century near the city is similar to the average of the Rift zone.

0.30

w J3 "a3 u u

< a 3

o

0.20

0.10

SH

o

HAZAN Mean + St .Dev. — - -HAZAN Mean Values - - - -EQRISK

« 0.00

1000 2000 Return Period (Years)

3000

Fig 9.9. Hazard curves for PGA in Sidon obtained using different probabilistic methods

This page is intentionally left blank

Chapter 10

Deterministic Assessment of Seismic Hazard Probabilistic seismic hazard assessment (PSHA) has become the most widely used approach to estimating the levels of earthquake actions to be considered in design. PSHA offers many advantages to the analyst, amongst which is the important feature of being able to assign return periods to different levels of ground motion - as has been done in this study - which provides a very convenient tool for selecting design motions for different performance levels and different importance categories of structures. Furthermore, PSHA allows all of the uncertainties associated with seismic hazard assessment to be taken into account, particularly those associated with size and location of future earthquakes. In addition to these features, normal PSHA procedures allow the effects of all the potential earthquakes that could affect a site to be amalgamated into a single expression of the hazard either as peak ground-motion parameters or response spectral ordinates. Despite these advantages of using PSHA, some researchers and practitioners have raised objections regarding certain features of the procedures, particularly with respect to site-specific assessments. The first issue of contention is that for long return periods, say of 1000 years and beyond, it is questionable whether the existing seismic catalogues, even including historical data such as that gathered for this study, justify such extensive extrapolation. Krinitzsky (1998) argues that a fundamental weakness in PSHA is the Gutenberg-Richter (G-R) recurrence relationship, which he argues holds only for extensive regions with high levels of seismic activity. Krinitzsky affirms that the G-R relationship hold neither for small areas that affect specific sites nor for individual faults. Furthermore, the GR relationship does not estimate temporal earthquakes, i.e. those that can happen during the lifetime of a structure. Krinitzsky goes on to show how the measures that are sometimes applied to remedy these shortcomings in the G-R magnitude-frequency relationship add further problems. 95

96

Elnashai and El Khoury

The uncertainty associated with each of the inputs to seismic hazard assessment is important and requires rational consideration. A particularly important source of uncertainty is the scatter associated with the strongmotion attenuation relationship. Standard practice in PSHA, including the EQRISK program of McGuire (1976), is to implicitly include this uncertainty, integrating across the scatter in the prediction of ground-motion parameters so that the calculations cover both the probability of an earthquake occurring that will generate a certain mean value of the groundmotion parameter in question and the probability that as a result of the scatter this mean value will be exceeded. The implicit inclusion of the scatter has a strong influence on the hazard calculations, often increasing the design level of PGA by as much as 50% for the 475-year return period. As the return period of the design motions increases, the scatter exerts a continually greater influence and in fact can come to dominate the hazard completely. Bommer et al. (2000) have shown that for a typical hazard scenario, if PSHA is used to determine the 10,000-year ground-motions (the level generally considered for safety critical structures such as nuclear power plants), then some 70% of the design ground motions are actually due directly to the scatter in the attenuation relationship rather than the severity of the underlying earthquake events. This feature of PSHA is of particular concern given the very crude way in which the scatter in attenuation relationships is measured, being based in effect on the ratio rather of predicted to observed values rather than the absolute difference, and hence influenced equally by strong and by very weak motions (Bommer & Martinez-Pereira, 2000). Furthermore, there is evidence to suggest that the measures of scatter in current use are over-estimated because epistemic and aleatory uncertainties are treated as equivalent. Epistemic uncertainty is the intra-event uncertainty, which is effectively the spatial variability of strong-motion parameters in a particular earthquake and which can be reduced by the collection of additional information. Aleatory uncertainty is the inter-event uncertainty and reflects the inherent uncertainty regarding the nature of future events, which is to say the temporal variability. The implicit uncertainty in current PSHA practice is that the spatial uncertainty of ground-motion predictions can be treated as the uncertainty of ground motions over time at a specific location (Anderson and Brune, 1999).

Earthquake Hazard in Lebanon

97

A particular difficulty encountered with PSHA is when the output from the hazard assessment needs to be expressed in terms of acceleration timehistories. If the option of response spectrum-compatible artificial timehistories, which have many serious drawbacks, is rejected, then the first step in obtaining either real or synthetic records is to define an earthquake scenario. The basic parameters of the scenario are the magnitude of the earthquake and its distance from the site of interest, neither of which is available as output from PSHA, which considers not a single scenario but rather all the possible earthquake scenarios. Methods have been developed to identify the scenarios that contribute most significantly to the hazard at a site and these procedures are now generally referred to as disaggregation of the hazard (Chapman 1995, McGuire 1995, Bazzurro and Cornell, 1999). However, it can be easily shown that if the hazard at a site is affected by more than one source of the seismicity, then it will often not be possible to define a unique event that is compatible with the hazard. One source zone, close to the site but with a low Mmax value, may control the hazard in terms of PGA and short-period spectral response, whereas a more distant source, capable of producing larger events, may control parameters such as PGV, PGD and long-period spectral ordinates. Bommer et al. (2000) have shown that in such situations a single hazard-consistent scenario can be defined but it will generally correspond to an earthquake that is, according to the established limits of the source zones, physically impossible. As a result of all of these factors, for site-specific seismic hazard assessment, and in particular for critical structures, many researchers and practitioners recommend that deterministic seismic hazard assessment (DSHA) be used. It is often stated in textbooks that the basis of DSHA is to assign the maximum credible earthquake in each source zone to the least favourable location for the site in question, calculate the resulting ground motions, and then adopt the most severe scenario for design (e.g. Reiter 1990, Kramer 1996). This representation of DSHA is actually an oversimplification and in practice it is a more refined exercise than what is suggested in the fleeting summaries offered in textbooks whose focus is very clearly geared towards PSHA. The selection of the design earthquake magnitude in DSHA is not approached in the same way as the selection of

98

Elnashai and El Khoury

the maximum credible earthquake in PSHA, since the former has far greater impact on the final results. In terms of location of the design earthquake, DSHA requires careful geological and geophysical investigation to identify and characterise capable faults located within a few tens of kilometres of the site. Advances in remote sensing technology and increased understanding of the geomorphological manifestations of active faults now make it increasing unlikely that earthquakes will occur on previously unknown faults, provided, of course, that sufficiently thorough investigations are carried out. If the seismic hazard at a site is assessed using the deterministic approach, then from an engineering perspective the output offers many advantages. Once the magnitude and location of the design earthquake has been fixed, any strong-motion parameter can immediately and directly estimated from attenuation relationships, providing both acceleration and displacement response spectra as well as parameters such as duration and peak ground velocity, that have applications to geotechnical engineering problems. In addition to this, if it is determined that the source of the design earthquake will be located within a few (< 15) kilometres of the site, then the assessment of design loads can also account for near-field effects, such as the possibility of strong accelerations in the vertical direction (Papazoglou and Elnashai, 1996). Furthermore, near-field effects due to the directivity of fault rupture can also be taken in account in estimating the design earthquake actions. Somerville et al. (1997) have derived factors to increase the predicted ordinates of spectral acceleration at intermediate and long periods for cases where it is expected that the fault will rupture towards the site, and conversely reduce the spectral ordinates for backward directivity. These factors actually represent a clear example of including additional information in the prediction of strong-motion parameters and consequently of reducing the epistemic uncertainty. The aleatory uncertainty, represented by questions regarding which segment of the fault will rupture and in which direction will it propagate, remain. It is worth noting that "near source" factors are included in the 1997 edition of the Uniform Building Code (UBC) that similarly increase the acceleration spectral ordinates for sites in Zone 4 (highest hazard) that are

Earthquake Hazard in Lebanon

99

located close to active faults. These factors, Na and Nv, are applied to the spectrum that is first constructed in the usual fashion, starting with a classification of the soil conditions at the site and the characterisation of the hazard at the site from the zonation map. The zonation map is produced by PSHA at a series of grid points covering the national territory. The application of the near source factors assumes that if a site is near to an active fault, then that fault will rupture and furthermore will rupture towards the site. Hence, the spectrum finally obtained for sites in Zone 4 near to active faults is obtained through a combination of probabilistic and deterministic approaches. A final point worthy of note is that it is often stated that a shortcoming of DSHA is that the degree of uncertainty or the probability of exceedance of the resulting design actions is unknown. It is true that since a deterministic scenario corresponds to a single seismic source zone rather than all of the sources defined for the region, the probability if exceedance of the resulting motions cannot be calculated using the total probability theorem as is the case for PSHA. Nonetheless, it is possible to obtain estimates of the probability of the earthquake scenario and hence of the resulting ground motions. Bommer et al. (2000) have shown that for a single source zone, the probability of exceedance associated with a design event can be estimated. Since it is very often the case that the hazard at a site is almost completely dominated by earthquakes within a single source zone, the probability estimated in this way will be close to that obtained from the total probability theorem considering all seismic sources. For a well-defined and extensive active fault such as the Yammouneh fault in Lebanon, once the activity rate on the fault (magnitude-frequency relationship) is estimated then the return period of an earthquake of the design magnitude can also be obtained directly. The return period of the specific design scenario can then be estimated by simply multiplying the probability related to the magnitude by the ratio of the rupture length of an earthquake of this size to the entire length of the capable fault. Furthermore, the probability of the actual level of ground motion being above the mean values predicted by an attenuation equation are treated in a transparent fashion in DSHA, by selection of the mean (50-percentile), the mean-plus-one-standard-deviation (84-percentile)

100

Elnashai and El Khoury

or any other particular probabilistic level. This approach contrasts with that of PSHA, in which, as discussed previously, the scatter in the attenuation relationship has an influence that grows continuously with the return period.

Chapter 11

Concluding Remarks on Seismic Hazard in Lebanon i)

ii)

iii)

iv) v)

vi) vii)

The probable overall slip rate across the Dead Sea Fault Zone is about 8-10 mm/yr, and this value may be used to constrain short- and longterm hazard assessment. The current interpretation of the GPS data (which may change) suggests that this rate applies to the entire length of the zone between Aqaba and Antakya, and that a substantial proportion of the Arabia-Africa motion does not continue offshore south of Beirut along the Roum fault. However, because of the oblique orientation of the Yammouneh fault relative to the Arabia-Africa slip vector it is extremely likely that other faults (possibly including the Roum fault) are active between 31°N and 35°N. Some seismic activity occurs offshore between Beirut and Cyprus. It is likely that the Yammouneh fault segment of the Dead Sea fault system moves in earthquakes of Mw 7.2-7.5 that recur, on average, every 200-500 years. Equations (A) may be used in a hazard analysis with the understanding that the use of equation (Al-2) will require the use of near-field attenuation laws for much of Lebanon. Other, adjacent, faults in the same region are also capable of producing significant earthquakes. The earthquake activity of the 20th century, which was low, is definitely not a reliable guide to the short- or long-term seismic activity in the region. The 20th century seismic activity of the whole, tectonically active region has been remarkably low, and that in reality, the single large event of 22.11.1995 in Aqaba tells us nothing in itself, except that earthquakes of the same magnitude of about 7 plus must be considered credible events throughout the entire region.

101

102

Elnashai and El Khoury

viii) Until we understand why the larger earthquakes occurred where they did and how other parts of the region are genuinely different, the subdivision of the Levantine fault zone into seismotectonic provinces is not a realistic proposition particularly when using short-term seismicity data of 50 to 100 years, derived from an heterogeneous body of information. For this reason, the assumption of single area source zone following the trend of the Dead Sea Rift along the entire length of Lebanon is a reasonable and logical decision. ix) The Yammouneh fault is clearly capable of producing large earthquakes, based both on its dimensions, current tectonic deformation in the region and historical precedent. Therefore, it would be unconservative to neglect the important contribution of this fault to the seismic hazard within Lebanon, and hence the decision was taken to model it is as a separate and independent source from the area source representing the Dead Sea Rift, to which only large earthquakes are assigned. x) There are, to date, no earthquake strong-motion accelerograms that have been recorded within the Lebanon, hence it is unavoidable that attenuation equations need to be adopted from other regions. The relationships chosen, for peak ground acceleration and peak ground displacement, are derived from extensive, high-quality datasets of records from Europe, North Africa and the Middle East, and can reasonably be assumed to be applicable to Lebanon. The applicability of the PGA equations is at least partly confirmed by recordings of the Aqaba earthquake of 1995. xi) Hazard maps have been produced for three different return periods (475, 1000 and 2,5000 years) for several ground-motion parameters: PGA, PGD and ordinates of SA and SD at different response periods. These maps show a realistic distribution of seismic hazard throughout Lebanon, with appreciable hazard at all locations and particularly high hazard in Bekaa valley and at other locations close to the Yamouneh fault. xii) The hazard maps for the whole country have been derived assuming 'average' soil conditions, which have is essentially equivalent to assuming stiff soil. Therefore, for sites on rock, the values of the ground-motion and spectral parameters should be reduced and for

Earthquake Hazard in Lebanon

103

soft soil sites they need to be increased. For locations within Lebanon, Sidon and Tripoli, soil-dependent site-specific spectra of acceleration and displacement have been presented, and these can be used directly. The relative levels of spectral ordinates for rock and soft soil sites with respect to stiff soil sites can be obtained from these site-specific spectra. xiii) From an earthquake design view point, Lebanon is of medium activity, with peak ground accelerations in Beirut, Sidon and Tripoli for 475 years return period (corresponding to a structure design life of 50 years and a probability of this acceleration being exceeded of 10%, which is the standard code approach) is 0.16g. This places the three cities in a zone similar to the Uniform Building Code zone just above 2a. xiv) The forces imposed on a structure during an earthquake are proportional to the peak ground acceleration and inversely proportional to the ability of the structure to absorb energy through ductile deformations. Assuming that non-seismically designed structures that are nonetheless well constructed have an energy absorption capacity represented by a response modification factor (R in US practice, q in European practice) of 1.5, the force on structures of this type can be estimated according to their height and weight. The same applies to buildings with some seismic detailing, for which a response modification factor of ~3 is estimated, and to fully ductile seismically detailed structures, for which a value of ~5 is assumed. The ensuing forces are given in Table 11.1. Table 11.1: Percentage of weight of RC building to be applied horizontally for a design life of 50 years, with a probability of the force being exceeded during the design life of 10% (normal structures). Poorly No seismic Medium Full seismic constructed detailing detailing detailing 7% 1-2 storeys* 29% 23% 11% 3-5 storeys 34% 7% 22% 12% 6-9 storeys 22% 14% 7% 5% 10-14 storeys 3% 2% 10% 6% 14-20 storeys 2% 1.2% 6% 4% *Values for 1-2 storey ductile structures are divided by 0.83R (or q) since short period structures benefit less from ductility.

104

Elnashai and El Khoury

Using the same procedure for important structures (either a probability of the load being exceeded of 5% or a design life of 100 years) values of design base shear may be obtained from the hazard maps with a return period of 1000 years given below. Table 11.2: Recalculated earthquakes within 27° to 37°N and 34° to 37°E 1900 to 1999 Y 1900 1903 1903 1903 1905 1906 1907 1907 1910 1911 1912 1913 1918 1919 1921 1921 1921 1921 1921 1922 1923 1924 1924 1925 1926 1927 1927 1927 1927 1927 1928 1928 1928 1928 1928 1928 1929 1929 1929 1930 1930

M 01 03 05 10 12 02 06 06 07 07 03 11 09 08 02 04 04 09 10 04 02 02 02 03 10 04 05 07 07 09 01 02 02 08 08 11 03 05 05 01 03

D 05 29 10 07 06 23 10 22 10 13 29 19 29 19 05 20 21 05 05 02 27 18 27 16 11 14 02 11 17 24 18 09 22 05 23 04 24 16 28 13 07

OT 0015 2343 1800 1115 0000 0728 1210 1532 1924 0000 2115 1324 1207 2017 1909 1604 0800 1910 0609 0046 1815 1703 2024 0630 0429 1317 0620 1303 0806 0027 0555 2022 1751 0342 0615 0334 1211 0122 0640 0240 2300

N° 34.00 32.22 32.2 36.5 35.60 34.30 33.70 33.70 34.00 33.80 35.55 33.00 35.10 35.20 36.00 34.00 33.00 36.50 36.40 34.80 32.70 34.80 33.30 33.40 33.30 36.10 34.00 31.80 32.00 29.00 32.00 34.10 32.00 32.50 30.40 32.00 32.00 36.50 35.20 33.80 32.70

E° 34.50 35.26 35.5 36.5 35.90 34.00 35.50 35.50 36.00 35.40 35.77 35.80 34.80 34.70 35.50 35.40 35.50 36.50 35.20 34.80 35.40 34.30 34.30 36.20 36.50 36.20 34.00 35.70 35.50 35.00 35.50 35.90 35.40 35.70 35.72 35.60 35.50 36.00 36.40 35.80 36.50

R h 2 00 3 00 3 00 3 00 3 00 4 00 2 00 2 00 3 00 0 00 3 00 3 00 4 00 2 00 2 00 4 00 0 00 3 00 2 00 2 00 0 00 4 00 3 00 0 00 0 00 0 00 4 00 3 00 3 00 4 00 3 00 3 00 3 00 3 00 4 00 3 00 2 00 2 00 3 00 3 00 3 00

M« 5.80 5.00 0.00 4.75 0.00 5.31 4.00 4.30 4.63 0.00 4.00 4.30 6.26 5.38 4.80 5.38 0.00 0.00 4.05 4.65 0.00 6.01 4.90 0.00 0.00 0.00 4.60 6.05 0.00 4.20 0.00 0.00 4.80 4.50 5.00 0.00 0.00 4.55 0.00 0.00 0.00

q 1 1 0 1 0 1 1 1 1 0 1 1 1 1 1 1 0 0 1 1 0 1 1 0 0 0 1 1 0 1 0 0 1 1 1 0 0 1 0 0 0

logM„ 25.07 24.24 00.00 23.99 00.00 24.55 23.24 23.54 23.87 00.00 23.24 23.54 25.61 24.62 24.04 24.62 00.00 00.00 23.29 23.89 00.00 25.31 24.14 00.00 00.00 00.00 23.84 25.35 00.00 23.44 00.00 00.00 24.04 23.74 24.24 00.00 00.00 23.79 00.00 00.00 00.00

r 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

M 5.98 5.43 0.00 5.26 0.00 5.64 4.76 4.96 5.18 0.00 4.76 4.96 6.34 5.68 5.30 5.68 0.00 0.00 4.80 5.20 0.00 6.14 5.36 0.00 0.00 0.00 5.16 6.17 0.00 4.90 0.00 0.00 5.30 5.10 5.43 0.00 0.00 5.13 0.00 0.00 0.00

Mk 0.0 5.6 0.0 0.0 0.0 0.0 4.4 4.2 4.7 0.0 0.0 0.0 6.5 5.4 0.0 5.2 0.0 4.5 0.0 5.5

Mp 0.0 6.0 0.0 0.0 4.5 0.0 4.8 4.9 4.6 0.0 0.0 4.0 6.5 5.9 5.0 5.1 4.0 0.0 4.0 5.5

Mb 0.0 5.5 0.0 0.0 0.0 0.0 4.7 5.0 5.0 4.0 0.0 4.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Ma 0.0 5.6 0.0 0.0 0.0 0.0 4.7 5.7 5.0 3.5 0.0 4.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

N ra„ 000 000 000 002 000 012 002 000 002 000 000 001 050 020 000 016 000 001 001 001

4.2 5.8 5.1 0.0 0.0 0.0 0.0 6.0 4.1 4.8 4.2 4.8 5.2 4.4 0.0 0.0 0.0 0.0 0.0

0.0 6.0 5.8 0.0 0.0 0.0 0.0 7.2 0.0 0.0 0.0 4.7 4.6 0.0 0.0 4.2 0.0 0.0 0.0

4.3 0.0 5.0 4.0 3.5 4.4 0.0 6.3 4.5 5.0 4.2 0.0 5.0 4.4 0.0 0.0 0.0 0.0 0.0

3.5 0.0 5.7 0.0 0.0 0.0 0.0 6.2 4.5 0.0 4.2 0.0 5.5 4.0 0.0 4.2 0.0 0.0 0.0

000 053 001 000 001 001 009 079 000 005 001 001 003 001 028 000 004 013 001

0.0 0.0

4.0 4.2

0.0 0.0

0.0 001 0.0 001

Earthquake Hazard in Lebanon Y 1930 1930 1930 1930 1930 1930 1935 1936 1937 1937 1938 1938 1939 1940 1940 1940 1940 1941 1942 1943 1944 1944 1945 1947 1947 1947 1949 1949 1949 1950 1950 1951 1951 1951 1952 1952 1952 1952 1953 1954 1954 1954 1954 1954 1955 1956 1956 1956 1957 1957 1957 1957 1957

M D 03 25 05 21 06 14 09 14 11 18 12 17 10 19 06 14 09 13 10 12 02 01 07 01 03 20 01 27 07 24 09 02 12 09 12 17 09 28 09 10 04 24 10 07 10 24 04 03 09 15 12 09 01 01 04 14 10 28 01 01 03 01 04 08 07 12 08 05 03 22 10 22 11 18 12 28 05 24 01 26 03 13 04 01 09 13 11 08 12 27 03 16 03 16 12 18 02 02 03 03 05 14 07 18 07 29

OT 1858 1045 1932 0223 1312 0202 0827 1701 0850 0958 1209 0107 1636 0533 2215 1032 2036 1343 0117 0652 1824 1030 1738 1431 0040 2340 1655 1230 1910 2219 2130 2138 0651 1512 0452 1700 1905 0242 2117 0246 0233 1727 2146 0324 0201 1932 1942 1753 0033 1824 0025 0824 0119

N°

E°

33.80 35.80 32.20 35.50 34.30 36.50 34.80 36.60 34.40 36.60 36.10 36.20 36.20 35.90 36.78 35.74 34.50 36.70 31.30 35.40 36.20 37.00 36.80 36.80 36.80 36.80 32.80 35.40 34.50 34.45 31.90 35.60 34.80 36.30 36.20 36.40 34.40 36.60 32.50 35.30 33.80 35.80 32.90 35.50 33.90 36.20 34.00 36.70 32.70 35.50 36.46 34.66 36.50 35.40 32.70 35.60 33.00 35.50 36.50 35.80 33.00 35.50 36.60 35.90 36.50 36.30 34.10 36.10 27.20 34.50 36.97 35.73 34.20 36.20 32.60 35.30 37,00 37.00 33.90 36.40 34.40 34.20 33.70 36.10 30.80 35.50 34.30 36.00 33.70 36.30 33.60 35.40 33.60 35.50 31.40 35.50 33.60 35.40 34.00 34.00 33.80 35.90 33.70 34.70 34.60 36.80

105 R 3 3 3 3 3 3 3

h 00 00 00 00 00 00 00

4 10 2 3 3 3 3 3 4 3 2 3 2 3 2 3

00 00 00 00 00 00 40 00 00 00 00 00 00 00

200 2 3 4 2 3 3 2 3 4 2 4 1 3 2 3 2 2 2 2 4 2 2 3 3 3 3 2 2 3 3

00 00 30 00 00 00 00 00 45 00 00 00 34 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

M5 q 0.00 0 4.4 1 0.00 0 4.50 0 0.00 0 0.00 0 0.00 0 5.40 1 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 4.84 1 4.50 1 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 5.39 1 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 5.75 1 0.00 0 4.33 1 4.81 1 5.37 1 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 4.53 1 0.00 0 0.00 0 4.84 1 5.06 1 4.93 1 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0

logM„ 00.00 23.64 00.00 23.70 00.00 00.00 00.00 24.64 00.00 00.00 00.00 00.00 00.00 00.00 24.08 23.74 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 25.01 00.00 23.57 24.05 24.61 00.00 00.00 00.00 00.00 00.00 00.00 23.77 00.00 00.00 24.08 24.30 24.27 00.00 00.00 00.00 00.00 00.00

r 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

M 0.00 5.03 0.00 5.10 0.00 0.00 0.00 5.70 0.00 0.00 0.00 0.00 0.00 0.00 5.32 5.10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.94 0.00 4.98 5.30 5.68 0.00 0.00 0.00 0.00 0.00 0.00 5.12 0.00 0.00 5.32 5.47 5.45 0.00 0.00 0.00 0.00 0.00

Mk 0.0 4.2 0.0 0.0 3.8 0.0 0.0 5.5 0.0 4.2 0.0 0.0 0.0 4.2 5.4 4.4 0.0 0.0 0.0 5.0 0.0 4.4 0.0 0.0 4.0 5.6 0.0 0.0 0.0 0.0 0.0 5.7 0.0 4.7 0.0 5.5 0.0 4.2 0.0 0.0 0.0 0.0 4.8 0.0 0.0 4.9 5.1 5.5 0.0 0.0 0.0 0.0 4.2

Mp 0.0 4.9 3.5 4.5 4.2 4.5 4.2 0.0 3.8 4.5 4.4 4.2 4.0 4.0 5.7 0.0 3.5 4.0 4.0 5.0 3.0 4.0 3.8 3.8 0.0 5.8 0.0 0.0 0.0 4.5 0.0 6.2 4.8 5.0 0.0 5.2 3.5 4.0 5.2 3.8 4.0 4.0 5.2 3.5 4.0 5.5 5.8 5.7 0.0 0.0 0.0 0.0 4.5

Mb 0.0 4.3 0.0 4.5 4.0 0.0 0.0 0.0 0.0 4.2 0.0 0.0 0.0 4.4 0.0 4.5 0.0 0.0 4.2 4.8 0.0 4.3 0.0 0.0 4.0 0.0 0.0 0.0 4.4 0.0 4.0 0.0 0.0 5.0 0.0 0.0 0.0 4.2 0.0 0.0 0.0 4.0 5.0 0.0 0.0 6.1 0.0 4.9 0.0 0.0 0.0 0.0 4.2

Ma 0.0 4.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.0 0.0 0.0 0.0 4.5 0.0 4.5 0.0 0.0 0.0 4.7 0.0 0.0 0.0 0.0 4.5 0.0 0.0 0.0 4.0 0.0 4.0 0.0 0.0 5.0 0.0 0.0 0.0 4.0 0.0 0.0 0.0 0.0 5.5 0.0 0.0 5.3 6.0 6.0 0.0 3.0 0.0 4.5 0.0

N rat,

001 001 001 001 001 001 001 069 001 002 001 001 002 001 032 002 001 001 001 003 001 002 001 001 001 066 000 001 001 002 000 127 001 037 020 122 001 001 001 001 001 000 017 000 000 060 060 073 003 003 001 001 001

106 Y 1957 1958 1958 1958 1958 1958 1958 1958 1958 1959 1959 1959 1959 1959 1959 1959 1959 1959 1959 1960 1960 1960 1960 1960 1960 1960 1960 1961 1961 1961 1962 1962 1963 1963 1963 1964 1964 1964 1964 1964 1964 1965 1965 1965 1965 1966 1967 1968 1968 1968 1969 1969 1969

Elnashai and El Khoury M 11 02 08 09 10 10 10 11 11 04 04 04 05 06 07 10 10 11 11 01 03 04 04 05 05 06 08 09 09 10 02 10 04 05 11 02 05 07 11 12 12 04 04 05 08 06 07 03 04 06 03 05 05

D 03 14 12 09 01 12 16 05 24 10 11 19 21 25 12 07 29 10 29 28 21 22 28 03 19 30 28 10 22 11 01 13 14 21 03 02 12 15 17 15 30 01 16 02 24 26 21 26 09 16 31 10 24

OT

N°

0956 2359 0215 0021 0933 0636 2220 2046 1448 1323 0754 0214 0237 1244 1326 1514 1821 0201 2048 1936 1902 2227 0605 0226 1746 0215 0223 1617 0922 0354 0932 0326 2327 1924 0444 0626 2141 1724 2250 1731 0114 0111 2257 1151 0124 1317 2048 1937 1316 0834 1129 0927 1149

32.50 31.30 32.80 33.00 33.80 32.70 32.60 34.50 32.50 33.40 33.40 33.40 33.00 32.30 33.00 33.80 34.00 33.80 33.60 33.00 33.50 34.00 32.80 32.20 36.00 32.20 33.00 36.60 33.60 34.30 33.50 31.30 33.80 34.20 35.00 36.71 33.00 34.50 36.80 36.46 36.40 35.95 33.30 33.50 33.80 36.91 34.40 34.05 32.70 36.76 27.70 27.46 36.83

E° R h 35.90 35.60 34.20 34.50 35.90 34.00 35.50 36.50 36.00 35.60 35.60 35.50 35.50 35.30 35.50 35.80 34.00 34.80 35.00 35.50 35.60 36.00 35.50 36.20 34.00 35.40 35.40 35.80 34.60 35.00 35.00 35.60 34.00 34.40 35.00 35.41 34.60 34.50 35.43 34.80 34.20 35.77 34.20 35.30 35.00 36.02 34.20 35.49 35.60 34.34 34.07 34.10 35.34

2 00 3 00 2 00 0 00 2 00 0 00 2 00 2 00 2 00 2 00 2 00 2 00 2 00 2 00 2 00 2 00 8 00 0 00 0 00 0 00 0 0 2 00 2 00 2 00 8 2 2 8 0 0 0 0 2 2 2 4 2 2 4 1 1 1 0 2 2 7 1 7 0 7 7 7 7

00 00 00 00 00 00 00 00 00 00 00 38 00 00 00 41 99 40 00 00 00 47 99 25 00 50 19 23 51

M, q 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.00 3.72

0

0 0 0 0 0 0 0 0 0 0 0 0 0 1 1

logM„ 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 00.00 24.24 22.96

r 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

M 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.43 4.58

Mk 4.5 4.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 00 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.6 0.0 0.0 0.0 0.0 0.0

Mp 4.0 0.0 0.0 0.0 3.7 0.0 3.0 0.0 0.0 3.6 0.0 3.7 3.0 0.0 0.0 3.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.2 0.0 2.6 2.8 3.3 0.0 3.0 3.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 5.0 0.0 0.0 0.0 0.0 0.0

Mb 4.5 4.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.1 0.0 0.0 0.0 0.0 4.0 0.0 0.0 0.0 0.0

Ma 5.5 4.0 0.0 3.0 0.0 3.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3.0 3.0 3.0 0.0 0.0 0.0 3.0 3.0 0.0 3.0 3.0 0.0 3.0 3.0 3.5 3.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3.9 3.5 0.0 0.0 4.8 0.0 0.0 0.0 0.0 0.0

N

mb

001 001 001 003 001 003 001 001 001 001 001 001 001 001 001 001 000 003 003 000 001 001 001 001 000 001 001 000 003 003 000 003 001 001 001

on

002 002 024 4.5 012 4.1

007 025 4.3

002 002 003 028 4.5 014 4.3 050 4.8

002 039 4.4 013 4.6 090 4.7 054 4.4

Earthquake Hazard in Lebanon Y 1969 1970 1971 1971 1972 1973 1973 1975 1979 1980 1981 1981 1981 1982 1982 1982 1982 1983 1983 1983 1984 1984 1985 1985 1987 1987 1988 1989 1990 1991 1991 1992 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993

M 08 10 04 11 02 09 11 01 04 01 02 02 06 01 03 10 12 02 02 06 08 12 01 12 06 09 08 06 09 08 09 03 03 07 07 08 08 08 08 08 08 08 08 08 08 08 08 08 08 08 10 10 11

D 09 08 16 08 08 02 08 01 23 02 19 24 30 19 23 30 19 03 03 03 24 18 25 31 16 06 03 24 13 14 19 09 22 30 31 03 03 03 03 03 03 03 03 03 03 07 09 13 13 20 18 21 03

OT 1328 0245 2127 1755 0551 0401 1549 0030 1302 1252 0241 2241 0759 1838 1048 0436 1917 1346 2330 0204 0602 1359 0608 1942 0617 0905 2042 0310 2210 1341 0214 1954 1103 2334 1753 1243 1254 1312 1329 1333 1345 1633 1750 1802 2053 0455 0605 0031 0111 2310 2051 0035 1839

N° 27.50 31.70 33.65 33.30 33.90 32.80 35.50 36.73 31.15 36.56 36.13 36.49 36.14 35.97 27.86 27.78 34.8* 29.15 29.24 33.81 32.90 35.27 31.90 29.12 35.34 27.04 35.86 36.75 27.21 36.04 36.05 34.35 34.71 28.83 29.29 28.71 28.65 28.59 28.85 28.35 28.60 28.78 28.67 29.03 28.78 28.79 28.80 28.62 29.06 28.83 29.00 28.80 28.70

E° 34.00 35.30 35.48 35.50 36.20 35.30 36.20 36.48 35.45 36.35 36.39 36.14 35.85 35.56 34.41 34.04 34.08 3483 34.81 35.83 34.83 35.28 35.51 34.98 35.27 35.21 35.71 35.91 35.14 35.87 35.75 35.93 34.40 34.76 34.87 34.55 34.77 34.73 34.57 34.75 34.54 34.64 34.88 34.48 34.64 34.61 34.61 34.69 34.60 34.62 34.81 34.71 34.67

R h 1 30 1 00 7 15 0 00 0 00 1 08 1 33 7 28 7 32 7 39 7 49 7 30 7 66 7 47 7 15 7 09 7 32 7 08 7 02 7 02 4 15 7 41 7 18 7 01 7 25 7 01 7 25 7 48 7 09 7 44 7 25 7 04 7 30 7 01 7 10 7 22 7 20 7 20 7 08 7 12 7 10 7 12 7 13 7 08 7 02 7 01 7 01 7 14 7 18 7 10 7 16 7 11 7 06

107 Ms q l 0 0 0 0 0 0 l l 0 1 1 1 0 1 0 0 0 0 1 1 1 0 0 1 0 1 1 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 1 0 1 0 0 0 1 0 1

4.02 0.00 0.00 0.00 0.00 0.00 0.00 5.00 4.45 4.13 3.98 4.20 4.01 3.98 4.32 1.82 3.20 4.22 4.20 4.31 4.48 4.50 3.94 3.95 3.95 3.73 4.10 4.51 4.20 3.41 3.17 3.95 4.93 4.30 3.68 5.76 5.40 5.20 3.45 4.25 4.65 5.21 3.99 3.94 4.41 3.99 4.00 4.28 3.71 4.10 4.00 3.56 4.62

logM„ 23.26 00.00 00.00 00.00 00.00 00.00 00.00 24.24 23.77 23.37 23.22 23.44 23.25 23.22 23.56 21.06 22.44 23.46 23.44 23.55 24.02 23.74 23.18 23.19 23.19 22.97 23.34 23.70 23.44 22.65 22.41 23.19 24.15 23.54 22.92 25.26 24.64 24.44 22.69 23.49 23.89 24.67 23.23 23.18 23.65 23.23 23.24 23.52 22.95 23.34 23.24 22.80 23.86

r 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 1 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0

M 4.78 0.00 0.00 0.00 0.00 0.00 0.00 5.43 5.12 4.85 4.75 4.90 4.77 4.75 4.98 3.30 4.23 4.91 4.90 4.97 5.28 5.10 4.72 4.73 4.73 4.58 4.83 5.07 4.90 4.37 4.21 4.73 5.37 4.96 4.55 6.11 5.70 5.56 4.40 4.93 5.20 5.72 4.76 4.72 5.04 4.76 4.76 4.95 4.57 4.83 4.76 4.47 5.18

Mk 0.0 4.6 0.0 4.2 4.1 4.2 4.1 0.0 4.7 0.0 0.0 0.0 4.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.5 0.0 0.0 0.0 0.0 0.0 0.0 4.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Mp 0.0 00 00 00 4.2 4.2 4.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Mb Ma 0.0 4.6 0.0 4.2 0.0 4.8 0.0 0.0 5.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

N mi,

0.0 021 4.5 5.0 024 0.0 056 4.5 4.3 000 0.0 000 4.5 022 0.0 015 0.0 145 4.8 5.0 160 0.0 088 4.6 0.0 102 0.0 031 4.4 0.0 112 0.0 072 4.5 0.0 081 4.7 0.0 029 4.6 0.0 045 4.7 0.0 106 4.9 0.0 101 4.8 0.0 120 4.6 0.0 265 5.1 0.0 120 0.0 072 4.6 0.0 070 4.8 0.0 070 4.6 0.0 059 4.7 0.0 128 4.6 0.0 335 0.0 101 4.6 0.0 049 4.4 0.0 043 4.2 0.0 070 4.1 0.0 476 0.0 144 4.7 0.0 057 4.3 0.0 573 0.0 144 0.0 134 0.0 050 4.5 0.0 116 4.9 0.0 156 0.0 445 0.0 073 4.5 0.0 070 4.5 0.0 112 4.7 0.0 067 4.3 0.0 113 4.6 0.0 131 4.6 0.0 058 4.2 0.0 084 4.4 0.0 094 4.6 0.0 053 4.3 0.0 217

108 Y 1993 1993 1994 1994 1994 1995 1995 1995 1995 1995 1995 1995 1995 1995 1995 1995 1995 1995 1995 1995 1995 1995 1995 1996 1996 1996 1996 1996 1996 1996 1997 1997 1997 1997 1997 1997 1997 1997 1997 1998 1998 1998

Elnashai and El Khoury M 11 12 01 02 04 02 11 11 11 11 11 11 11 11 11 11 12 12 12 12 12 12 12 01 01 02 02 05 06 06 01 01 01 01 03 03 03 05 10 06 06 07

D 08 04 03 10 06 14 22 22 22 22 22 22 23 23 24 25 01 02 08 11 14 23 26 03 04 21 26 23 05 19 22 22 22 23 08 26 26 10 30 27 28 04

OT

N°

E*

0106 2334 2100 0615 2118 1247 0415 0755 1137 1247 2002 2216 0305 1807 1643 1141 2004 0047 0412 0132 0353 0629 0619 1005 1722 0459 0717 2045 1313 0018 1757 1824 1827 0709 1521 0422 1320 2301 1734 1355 0359 0215

28.74 28.88 36.99 36.95 28.78 35.79 28.78 29.07 28.85 28.56 29.17 28.71 28.92 29.28 29.06 29.21 29.27 29.41 29.99 28.91 28.97 29.67 29.15 28.76 28.71 28.86 28.68 34.81 35.78 36.00 36.22 36.20 36.21 36.26 27.44 33.39 33.72 28.23 34.89 36.89 36.94 36.87

34.67 34.92 35.83 35.84 34.62 34.26 34.81 34.74 34.99 35.01 34.84 34.92 34.93 34.84 34.80 34.89 35.02 35.12 34.89 34.82 34.81 35.11 35.33 34.97 34.81 34.80 35.00 34.68 35.54 35.86 35.93 35.83 35.87 36.17 34.63 35.40 35.48 34.82 35.07 35.24 35.44 35.29

R h M, 7 06 4.50 7 01 4.30 7 42 4.77 7 17 4.48 7 01 4.20 7 39 4.26 7 19 7.06 7 05 4.21 7 08 3.80 7 12 4.64 7 02 4.02 7 01 4.87 7 05 4.06 7 29 5.16 7 24 4.50 7 07 4.27 7 01 4.07 7 10 4.16 7 07 4.21 7 15 4.80 7 09 3.99 7 10 4.12 7 10 3.80 7 02 3.90 7 07 3.59 7 19 4.73 7 14 4.40 7 35 4.03 7 23 3.70 7 46 4.32 7 15 5.38 7 46 4.61 7 58 4.88 7 25 4.08 7 10 4.30 7 10 4.64 7 03 4.83 7 05 4.14 7 15 0.00 7 50 6.20 7 10 4.40 7 15 5.40

q l l l l 0 0 l 0 0 l 0 l 0 l l 0 0 0 0 l 0 0 l

I 0 1 1 0 1 0 1 1 1 0 1 1 1 1 0 1 1 1

logM„ 23.74 23.54 24.01 23.72 23.44 23.50 26.74 23.45 23.04 23.88 23.26 24.08 23.30 24.58 23.74 23.51 23.31 23.40 23.45 24.04 23.23 23.36 23.04 23.14 22.83 24.04 23.64 23.27 22.94 23.56 24.63 23.85 24.12 23.32 23.54 23.88 24.07 23.38 00.00 25.49 23.64 24.64

r 0 0 0 0 0 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0

M 5.10 4.96 5.28 5.05 4.90 4.94 7.10 4.90 4.63 4.94 4.78 5.32 4.80 5.66 5.10 4.94 4.84 4.87 4.90 5.30 4.76 4.84 4.63 4.70 4.49 5.30 5.03 4.78 4.56 4.98 5.69 5.17 5.35 4.82 4.96 5.19 5.32 4.86 0.00 6.26 5.03 5.70

Mk 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Mp 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Mb 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Ma 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 5.3 0.0 0.0 0.0 0.0 0.0 0.0 5.3 0.0 0.0 5.6 5.0 0.0 0.0 0.0 0.0 0.0

N

mb

190 074 282 145 101 4.5

123 756 103 4.8 062 4.4

286 076 4.4

276 079 4.6

451 218 124 4.8 080 4.3 093 4.4 104 4.3 304 4.9 073 4.2 086 4.3 110 4.5 146 4.9 054 4.0

311 239 5.0 077 4.0

123 161 4.4

545 384 5.1

306 082 4.3 109 4.8

316 151 190 4.7 000 4.2

000 000 000

OT= Origin Time, h = focal depth. Epicentral locations - R: 1 .BAAS/ISS/ISC, 2: adopted, 3: macro, 4: recalculated, 5: GR, 6: USGS, 7:Engdahl, 8; BCIS, 0: other. Magnitude Ms determinations - q : 0: from logN-Ms formula > 1979, 1: instrumental. Seismic moment M0 - r: 0: converted from Ms, 1: calculatedfrom CMT. Other surface-wave magnitudes - Ma Arieh et al. (1985) - Mb Ben-Menahem. (1979) - Mk Karnik(1996)-

Mp Plassard Kagoj (1981)

Appendix Al

Surface Wave Magnitude According to Abe (1981), M G R, the magnitude, which is based on surface-waves for shallow events first used by Gutenberg and Richter (1936), is equivalent to the surface-wave magnitude. MGR was devised in order to extend to teleseismic distances the local magnitude ML, which had been defined in the previous year (Richter, 1935) and more thoroughly developed in a subsequent paper (Gutenberg, 1945). The M G R original scale was based on the maximum horizontal ground displacement A™*, but it was specified that measurements were to be made at periods near 20s, although it is evident from Gutenberg's work-sheets, that quite often Gutenberg himself did not observe this rule. He used periods from 10 to 25 seconds, and quite often values that differ from those published in station bulletins. There are different interpretations of the structure of Gutenberg's magnitude MGR, of its changes over the time of its development and of the method this author used to choose maximum phase amplitudes, a subject which is outside the purpose of this report (Bath 1969, Abe 1981, Lienkaemper 1984). An improvement of the scale was made by Soloviev (1955) who proposed a surface-wave magnitude in which the maximum ground particle velocity (A/r) max , a physical quantity which accounts better for the seismic energy flux at a seismographic station than the ground displacement A ^ at 20 sec period, was used as the variable. Soloviev's scale is not restricted to a given period, and Ms can be calculated within a broad range of distances of 4° to 80°. He defined the general formula for the station surface-wave magnitude M Si as MSii = log(A/Dmax + s(D,h) + C

(Al-1)

where A is the ground displacement in micrometres, T is the period in seconds associated with the maximum particle velocity (ATT^x, s(D,h) is 109

110

Elnashai and El Khoury

an empirical ground velocity-distance calibration function which expresses the change of particle velocity with epicentral distance D and focal depth h, and C is a correction term which allows for the effects at the recording site, wave path, variations in depth and focal mechanism (Soloviev and Shebalin 1957). Karnik et al. (1962) and Vanek et al. (1962), following Soloviev, proposed the calibration relation, S(D) = 1.661og(D) + 3.3

(Al-2)

which they derived originally from the weighted average of 14 attenuation functions existing at the time for epicentral distances between 20° and 160° and for an wide range of surface wave periods. These 14 attenuation function, and subsequent functions used to control equation (Al-2) are given in Soloviev (1961, p.l 15), Karnik (1968, pp.56-60), cf. Lienkaemper (1984). Later, the validity of equation (Al-2) was confirmed further for smaller distances of a few degrees by Karnik and Christoskov (1977) and Karnik (1977). Calibration relation (Al-2) was adopted by IASPEI in 1967, specifically in order to avoid the limitations imposed by the restriction to near 20-second period waves in Gutenberg's method. Equation (Al-1), commonly referred to as the original "Prague formula", was then defined as M s = log(A/T)max + 1.661og(D°) + 3.3 + Q

(Al-3)

where Q is a station correction term which allows for the effects at the recording site and wave path. Recommended period ranges corresponding to maximum amplitudes of surface waves at different epicentral distances were also given by IASPEI (1967), Karnik (1962) and Willmore (1979). The Prague formula was devised to be used with shallow events (h<40-50 km) and to have a depth adjustment for deeper events. We will not discuss here the derivation of depth correction (e.g. Ambraseys and Free 1997, and Herak et al. 1999) since the earthquakes of greatest interest in this study are all crustal.

Earthquake Hazard in Lebanon

111

However, with few exceptions, workers and agencies do not use the Prague formula according to its original definition. Since the mid-to-late 1970s, surface-wave magnitudes reported by both the National Earthquake Information Service (NEIS) and by the International Seismological Centre (ISC) have been computed and published using the Prague formula, but each agency selects data using different criteria that are not consistent with the definition of the original Prague formula. Up to 1975 NEIS published estimates of M s from readings on horizontal components at individual stations, but from May 1975 the assessment has been made only from the vertical component of the surface wave within the restricted period range 18 to 22 seconds and for distances between 20° and 160° (e.g. Lienkaemper 1984). It is theoretically more correct to use the vertical components rather than the horizontal ones because the vertical component records only waves of Rayleigh type, while the horizontal components record both Love and Rayleigh waves, with resulting complication in attenuation characteristics. No depth or station corrections are applied by NEIS and M s magnitudes are not generally computed for events with focal depths greater than 50 km. Before 1971 ISC neither reported long-period amplitudes and periods nor calculated M s . Between 1971 and 1976 ISC reported amplitudes and periods for all components, and Ms was calculated by combining vectorially the maximum reported amplitudes of the two horizontal components at periods near 20 seconds for stations in the distance range 20° to 160°, and using the attenuation relationship from the Prague formula. These determinations were given with the station readings only and were not included with the epicentres. Between 1976 and 1978 magnitude determinations from the vertical components were included for very few events, the distance range was extended to between 5° and 160° and the range of allowable periods to between 10 and 60 seconds.

112

Elnashai and El Khoury

Since 1978 event magnitudes determined using these criteria have been given with epicentres, but for the whole period up to today only those stations at distances between 20° and 160° are used in the averaging for an event magnitude and given as ISC M s estimates, and only for events at depths of 60 km or less. Thus M s magnitudes reported by ISC are calculated with the exclusion of amplitude and period data from distances smaller than 20° which implies, for instance, that no recordings from seismographic stations in the eastern Mediterranean region is used to calculate M s for earthquakes with epicentres in the region, which obviously is not necessarily true. NEIS and ISC thus use different selection criteria in choosing stations for the calculation of M s , and for a particular event the number of stations used and their distribution in azimuth may be different. In addition, ISC usually uses more station readings in determining event magnitudes than NEIS but neither of them report standard deviations of their estimates. Station correction Q in equation (Al-3) for a particular station i is defined as the mean of the residual Ms - MSiOver a period of time, i.e. Q = Z (Ms - MSi)/N, where M s is the event magnitude, MSi is the station magnitude and N is the number of events observed by the station. To the best of our knowledge, the first systematic estimation of station corrections from earthquakes in Europe was made by Karnik (1968) who employed the original Prague formula to assess corrections for 170, chiefly European stations. He used earthquakes in Europe and adjacent regions, of all magnitudes and depths, during the period between 1904 and 1951. Station corrections were calculated from shallow earthquakes in Iran (Ambraseys and Melville, 1982), for the Eurasian continent (Christoskov et al. 1983), Central American (Ambraseys 1995), world-wide (Rezapour and Pearce 1998) and for the Middle East up to longitude 70° east by Ambraseys and Douglas (1999). There is considerable discussion in the literature as to the best practice for the determination of surface-wave magnitude. Since its adoption by IASPEI in 1967 there has been much debate about the adequacy of the

Earthquake Hazard in Lebanon

113

amplitude-distance function of MSj in equation (Al-3) (Evernden 1971; Marshall and Basham 1973; Nuttli 1973; Seggern 1977; Christoskov et al.1983; Panza et al 1989; Herak and Herak 1993; Vanek 1995; Rezapour and Pearce 1998). It must be pointed out, however, that most of these authors examined the Prague formula at periods near 20s in the distance range 6° or 20° to 160° degrees, using Ms estimates made by NEIS or ISC, and not from station readings made according to the original definition of the scale. Ambraseys and Free (1997) examined the distance dependency of the residuals from station magnitudes and they found that the restriction of the data to the 18 to 22 seconds period range causes the original Prague formula to require a correction of its distance term for both global and regional data, and also that the selection of data over the much broader range implicit in the original version of the Prague formula reduces this requirement. They concluded that the distance dependence dM = Mi;3 - M u , where MJJ and My are the station magnitudes calculated without and with distance correction, remains statistically significant but small, dM = 0.518 -0.2821og(D)

(Al-4)

when they adhere to the original definition of the Prague formula (e.g. Ambraseys and Douglas 2000). However this correction becomes significant for magnitudes derived exclusively from few close in stations which is usually the case with small events. In the calculation of M s from damped instruments we used only ground amplitudes as reported in station bulletins. When trace amplitudes were given, because of the uncertainties in the calibration constants of early analogue seismographs these values were not converted into ground amplitudes and were not used. For the present study and for the period 1900 to 1915 amplitude and period data for the calculation of station magnitudes MSji were taken from station bulletins. For practical purposes our re-evaluation was divided into two broad, overlapping periods of observation, dictated chiefly by the type of

114

Elnashai and El Khoury

instruments available: an early period from 1892 to 1913 in which the majority of instruments world-wide were undamped or lightly damped pendula, and a second period from 1903 to 1915, of medium-period damped analogue recorders. One method to calculate an equivalent surface-wave magnitude MM for events in the early period, 1897 to 1913, is to use the maximum amplitude from the Milne penduli, culled from the Shide Circulars (1899-1913) and station bulletins, using the formula MM = log(A) + 1.251og(D) + 4.36

(Al-5)

where 2A is the peak-to-peak trace amplitude in millimetres on the single component of the Milne pendulum and D the epicentral distance in degrees. This formula was originally derived from earthquakes M s > 5.0 and D > 4° in Eastern Europe, the Mediterranean region, Iran, western Asia and Africa for which trace amplitudes for the calculation of MM as well as ground amplitude/period (A/T) data were available for the calculation of the corresponding value of M s (Ambraseys & Melville 1982). Equation (Al5) is used in this study to calculate MM earthquakes in the period 1897 to 1913. A similar relation, MA = log(A) + 1.661og(D) + 3.63

(Al-6)

was derived by Abe and Noguchi (1983) and Abe (1988) for large shallow earthquakes (M > 7.0) world-wide recorded at large distances. For the second period, which starts in 1903 with the operation of analogue seismographs in Europe at Potsdam, Gottingen, Uppsala and Leipzig, we used the original Prague formula and M s estimates were corrected for both station and distance (e.g. MSc) using the modified Prague formula (e.g. Ambraseys and Douglas 2000). Summarising, for earthquakes for which amplitude and period data from damped seismographs are available, Ms may be calculated from the Prague formula (Willmore 1979) or from its modified version, Msc with distance

Earthquake Hazard in Lebanon

115

and station corrections (e.g. Ambraseys and Douglas 1999, 2000; Ambraseys and Free 1997). For earthquakes for which amplitude and period data from damped mechanical instruments are lacking, trace amplitudes from Milne recorders may be used together with equation (Al5) or (Al-6) to assess equivalent magnitudes MMAbe's (1994) equivalent surface-wave magnitude MA, equation (Al-6), also may be used. It has been derived from large events (Ms > 7.0) recorded at large distances and for MM > 6.0, and gives values which are almost identical with those from equation (A 1-5). However, for smaller events, usually recorded at shorter distances (D < 30°), equation (Al-6) underestimates MM systematically by 0.1 to 0.3 magnitude units. There is some confusion in literature about the definition and use of seismic energy magnitude M w , moment magnitude M, and surface-wave magnitude M s . Kanamori (1977) defined the seismic energy magnitude M w as a linear transformation of the logarithm of the seismic moment M0 given by: M = M s = M w <= (2/3)log(M0) -10.73

(Al-7)

in which M0 in dyn.cm units (10~7 Nm). Kanamori derived equation (Al-7) from the observation that in most large, M s > 7.5, shallow earthquakes the stress-drop is about 30 bars, which he combined with the energy (E) and magnitude (Ms) relation for earthquakes in California, i.e. logE = 11.8 + 1.5MS which in reverse form, is similar to equation (Al-7). Moment magnitude M for shallow earthquakes in California in the range 5.0 < M s < 7.5, was then defined by Hanks and Kanamori (1979), as being equal to Mw from equation (Al-7). However, the equality M = M w = M s , as defined above, holds only for events that rupture the entire thickness of the seismogenic zone and its validity, therefore is regionally dependant (Ekstrom and Dziewonski, 1988). M is nothing more than a definition, or a transformation of M0 through equations (Al-12) and for the region of our interest M ^ M s for M s < 6.0.

Elnashai and El Khoury

116

Relations between surface wave magnitude M s and seismic moment Mo, and vice versa, provide suitable functions for the correlation between one source size indicator and the other. Current relationships for assessing M0 from the surface wave magnitude M s of shallow earthquakes have been derived from global or large sub-global datasets for active regions by Ekstrom and Dziewonski (1988), Rezapour and Price (1998), Perez (1999) and for stable continental regions Johnston (1996a,b). Ekstrom and Dziewonski (1988) derived global average relationships between Ms and logMo, in which the independent variable is logMo. They used 2,341 reported M0 values from the Preliminary Determination of Epicentres (PDE), and corresponding scalar moments from the Harvard CMT catalogue. Only events up to 1987, for which both the NEIC and the CMT depths are < 50 km, in the log(M0) range 23.5 to 28.6 were considered. A relationship was then determined in the form: M s = k - (a + b)/6 + logM0

for

logM0 < a

(Al-8a)

2

M s = k - (a + b)/6 + logM0 - QogM0 - a) /6(b - a) for a < logM0 < b

(Al -8b)

M s = k + (2/3)logM0

for logM0 > b

(Al-8c)

Note that equation (Al-8a) was derived on the assumption that the slope of the regression is one for logM0 < a, and equation (Al-8c) on the assumption that the slope is 2/3 for logMo > b. The constants in equations (A 1-8) were determined by minimising N X[Ms(logM0j;a,b,k) - Msi]2 with respect to a, b and k. Rather than summing over N i=l

earthquakes, a reduced data set was used in which M s was averaged for earthquakes in narrow bins of logM0 of 0.1 units, so that only about 40 summary data points were considered.

Earthquake Hazard in Lebanon

117

A good fit to the reduced data for earthquakes with moment as the independent variable in the range 2xl0 24 to 1028 dyn.cm was obtained with a = 24.5, b = 26.4 and k = -10.76, which reduce equations (Al-8) to: M s =-19.24+ logM0

for

logM 0 <24.5

(Al-9a)

M s = -19.24 + logM0 -0.088 (logM„ - 24.5)2 for 24.5 < logM0 < 26.4

(Al-9b)

M s =-10.76 + (2/3)logM0

(Al-9c)

for

logM 0 >26.4

These authors then rewrite equation (Al-9) in the form logMo = 19.24 + M s

for

M s < 5.3 0 5

logM0 = 30.20-[92.45-11.40M S ] -

for

logMo =16.14+1.5M S

M s > 6.8

for

(Al-lOa) 5.3<M S <6.8

(Al-lOb) (Al-lOc)

However, since equations (Al-10) are equations (Al-9) rewritten, formally, they are not the correct relationships for estimating logM0 from Ms Regional bias in Mo does exist and global average moment - magnitude relationships, such as (Al-9) and (Al-10), may be inappropriate for the assessment of long term seismic slip on faults, for the estimation of tectonic motion in regions, the rate of which is known from GPS measurements, and for the investigation of aseismic creep. Data show that the transition from a slope of unity to a larger value occurs at larger moments for continental events (Ekstrom 1987, Ekstrom and Dziewonski 1988) for which log(M0) = 19.24 + M s

for

M s <7.16

(Al-lla)

log(M0) = 15.66+ 1.5MS

for

M s >7.16

(Al-llb)

To overcome the problem with equations (Al-10) which have been derived by fitting the data with log(M0) as the independent variable, and at the same time to take into account the regional bias in equations (Al-9) and (Al-10), we derived the following set of bi-linear relationships log(M0) = 19.08 + M s

for

M s < 6.0

(Al-12a)

118

Elnashai and El Khoury

and log(M 0 )= 16.07+1.5M S

for

M s > 6.0

(Al-12b)

for the Eastern Mediterranean and the Middle East region up to 70°E, using CMT or P/SH moments and the corresponding uniformly reassessed M s values of 577 shallow (h < 40 km) earthquakes, in the logM0 range 22.4 to 27.3, in which M s is the independent variable.

Appendix A2

Application of Stepp Method In this method, the seismicity data (number of earthquakes) is grouped into different magnitude classes for different duration of time.

Table A2.1: Application of Stepp Method Time 1998-

6.75- 6.25-

5.75- 5.25- 4.75-

4.25-

3.75-

(years)

7.24

6.74

6.24

5.74 5.24

4.74

4.24

3.74

9

1

0

2

4

9

20

23

7

19

1

4

9

25

34

29

1

4

10

26

34

39

1

4

11

26

35

49

1

4

16

28

35

59

1

5

17

29

35

69

1

6

18

30

35

79

1

7

22

34

37

89

1

22

36

38

99

1

24

37

39

1QQH

19981980 19981970 19981960 19981950 19981940 19981930 19981920 19981910 1998-

9

1900

The mean rate of occurrence = ^ m = Nn/T 119

3.25-

120

Elnashai and El Khoury

The standard deviation of the mean = cm = *J(kJT) It is postulated that am is proportional to 1/VT. Therefore, if the data of magnitudes of earthquakes is complete, then the points should follow a relationship of the form log(om) oc 0.5 log(T)

From such a plot an idea can be had for the completeness of data within a given sample which follows a Poisson Process.

Appendix A3

Hazard Maps for Lebanon and Vicinity V\\\;H.,

iiMiPWERRftlSIEAN

•m^mm l

}

Wff h {

/

/

,

/

'

/

/

r/ /

/////

/

&

/

/

/

Qkmisc\is

TMv / /

////////

/

.

.

.

/

/

:

•'.;

/

- " / . - /•'•••• / - - . -

•/••.•••••/••••.•

•

•

/-

/

'

•

•

/

•

"S4

/

• / • • •

• '

/ . / / • • : - •

/ • '

•'.••'•

S^RIA 37

II •' • "

33

Fig A3.1. Hazard map of Lebanon in terms of peak ground accelerations (PGAg) for 475 years return period.

121

122

Elnashai and El Khoury

•\.-:"."35' %

Mi

'•-:m>

/ /

MEDITERRANEAN

:

•/•.-./•.

• • \

.••.•/•.'/••-.•'

37

v \ ^ V - " .

.

/

•

.

•

•

.

• •

/.

f / r TripaiJ

7 :

•

/

•

•

/.

•'••'••/

:

/ /

/5

••is/ ;/

/ J l&P?

/

drut/ F

/ //

/ ISayrfa

/

/

/

=34

^

# JT^I

J

/L $ * r g

^

5>

laamascus

SYRIA/ 37

::3Si;

f33t

36

/

33

Fig A3.2. Hazard map of Lebanon in terms of peak ground accelerations (PGAg) , in g, for 1000 years return period

123

Earthquake Hazard in Lebanon

ii

36 |

$SM

M.

•f::^ •/.^.•v.-A-\

::;&:

iMgipffiiRRAMEAN;;

•

/

]

:

/

f

m

/ /

ii&if

W ::^;v;::;-:;^:

/ f

/

/ !

/

Sj

i )J

/ _. / Tripoli

;\^.. 35-

/

/

f

/

M

£&•

•34.::

/

§f J

/

J /

P'

/

:;3s;:

::3T

F331

36

ili

• •'33'

Fig A3.3. Hazard map of Lebanon in terms of peak ground accelerations (PGA g ), in g, for 2500 years return period

124

Elnashai and El Khoury

Z%

^35::

m

\

/

xx \. v ;\35-

• . / • • • / .

. / - \ .

A . .

V

37

iMEBiiFERRAIStEAN:: /

/

J Si I^hLm^x ' / • ' -

iii^ii: if f f ^ * / /

::34:

- ™ / // .Mmm /

/

-

.

/

.-* / net =34

/

;:::7:H::Jpjru( /

f

:

'

/ /

//

/

*' IL , ,

/ Damascus

IIUUM&N

/

/

/

37

3SH f33J:

361;

33

Fig A3.4. Hazard map of Lebanon in terms of peak ground displacements (PGD cra ), in cm, for 475 years return period

Earthquake Hazard in Lebanon

125

m

38 /: J i

'••'

I

1

u r/n\ j fjjjl //i j />'w / f Yip

/

:/

r '•M/y

w

fir::-.:i

/ / / / I

:;&?

/ / / *»

#

f / / // r\

f47 7

7/

lilt / /

li K / / /

in/ Ipiliii/

/>// / // ft* / ,

"" 11/ (]/ / I ill

'

/

/

/

.

"

/

,

"

•

•

-34

$

7:-7 /

:/

/ /

/

•

/

.

•

:

/

•

•

Damascus .7 .,;.

vmS¥Rp ../

:37;:

l!3S::

33

Fig A3.5. Hazard map of Lebanon in terms of peak ground displacements (PGDcm), in cm, for 1000 years return period

Elnashai and El Khoury

126

-.35:!3S!::

M.: MEBifERRftlSiEftM

;

i3*=

'34

a¥ni#t ::3SH

• • ' • • 3 . 7 - . :•

:33s Fig A3.6. Hazard map of Lebanon in terms of peak ground displacements (PGD cm ), in cm, for 2500 years return period

127

Earthquake Hazard in Lebanon

M

-SSi;

'•% -

i:S5:i

iiWEPiliirgRRiftKEftNJii

• s v ^ * . -

'•••

•• ••

ut^m.

.'•^.^•^•..•.V.-.)4«^|

if/ '•Wf

Jejrut

/ #S&yd4

/ / / 7/ # / i:3Si:

f33

,

Damascus

/ '

'' If

37 ;3? sseesssj..

Fig A3.7. Uniform Hazard map of Lebanon in terms of Spectral Acceleration (SAg), in g, for 0.1 sec period of structure with 5% damping for 475 years return period

128

Elnashai and El Khoury

m

i:3S;i

• '•'• > t - V v - v .^"WW-XX

/A

MEDITERRANEAN

L r l

?

Jrfx\i4 jT

FH&hwJ/•;•••,.•;

mi>•/•/•/rMo:

!

/ ////

/ //mif/l

P* ?/ / // // // / / / A / / * t

ITA

H//////////mxf\.

::S4:?

f / / / /

m/

/ ///

*4fcfafc/ / i* i A

! ;; as;:

•/• •

'mm/J- /•••'/'- .

"S4

/ / / / //%4J6\»^.

/ ;/?//?/?

/

.

W

//

j* #

•

i / --

/ //ST/ / U J* i ''--••

' " # J ^ ' " '-'/aVRiA

i «./: •M-

37 •33 <**="»:

Fig A3.8. Uniform Hazard map of Lebanon in terms of Spectral Acceleration (SA g ), in g, for 0.3 sec period of structures with 5% damping for 475 years return period

Earthquake Hazard in Lebanon

129

-$SM

37:

\m: MEDITERRANEAN

f

iMwmm m

# ? # J/////W//'-

m-

*34

m.nj/fJl/JJj/J ..... 37:

im\ :

SZ

•Ani

•

/

,

!

If

S3

Fig A3.9 Uniform Hazard map of Lebanon in terms of Spectral Acceleration (SAg), in g, for 0.6 sec period of structures with 5% damping for 475 years return period

130

Elnashai and El Khoury

3Si; ::35:i

\mmmmmmm

m^mmmmmm-.

i^j

;i!:^;:i^:^::\

mi 5

a-^- ?

*(?.%

m

-./••-•

Jpp*^ /

^34

:M* Beirut

**"

fSayda'

LEBANON

Damascus

SYRIA r:y:.: M-

i:3Sh

ISIS Fig A3.10. Uniform Hazard map of Lebanon in terms of Spectral Acceleration (SA g ), in g, for 1.2 sec period of structures with 5% damping for 475 years return period

Earthquake Hazard in Lebanon

131

m ;:35;::

•37

MEDITERRANEAN:

:/S-.:F

r

rpc

/

/

/

/

f'

7

/

a rut

f

i;3gi; f33;

I/ /

i

M3J3J k?::-'.-'J ;i:

/ /

34

/

<&7

/7 / / / f

S

f

/

mm EB ihjb
/

/

/ /

/

*m

/

/ J /

/ /

ii&i*

/

/

/ Darrmscu^

(

/

l

i

5|

33

PlJ :W-

M

•..•:33"

Fig A3.11 Uniform Hazard map of Lebanon in terms of Spectral Acceleration (SA g ), in g, for 2.0 sec period of structures with 5% damping for 475 years return period

Elnashai and El Khoury

132

3§:l

i;35:i

MEDITERRANEAN

I )W1I

/ /

• / : • ' • • / ; " / • / " • • • ' • / / • • / • •

i ///I // o-u/ /// /am • / /

/ / A ::3* = •

/

^

#

•'

Ut.

iiiiijiiiiiiiir

/

/

• /

111

• • • / IQ

7

/ / /

/

•

'

•

•

/

/

'

/

/

'

•34

/,

>

/

/ /

••/••

J&*

/ -

x5

,..."W/ : '.'f;-v

iiii :i3S|:

37 3fi

S3

Fig A3.12.Uniform Hazard map of Lebanon in terms of Spectral Displacements (SDcm ) for 0.1 sec period of structures with 5% damping for 475 years return period

Earthquake Hazard in Lebanon

133

«S|:

•

#

•

A ; :^'-\ :

\^ ^\x> Xx>x •'••V:

'tmm.

/

:

•

V ^ ^ x

::35::

WW im

:/:/>

mm 'tm

iMEDPERRftNlI^N:;

W) 7 //

#

i /J; / /

l /

<

f**f

v

ffiwSiy /

7 // / / /

i&

/ /

#

?f$£ m*

'/

/? / F / /

/

/

%

:

'

•

/

r

Ms

fo

•

•

'

/

•

/

•

-

-

•

•

• • / • •

-}-• i •'-•'I/

•

/

""'/:'••'' •

'

•

/

-

'

•

•

•

•

'

•

. : / ' • • • ' .

f / / 9s*, ftff•:/•

/I

/ / / / / ( f .1*

Je,tftst/ / / / / / / /

•-'/

n4/^ / /

/

f

/

/

:/ /. / /

y

=34-

?* *> ,£:

/ / / / / / / /

,# : P

JJ / / / if / / f

/ / / / /

damasks i

/

Hi i-i\ fMj&ffim-

' • / • • / • . / - . - /

/'J^J

•rf^J:

•'}:;'•:

:!SS:: 3: X ,

f

I, - -

K

37,

-$$

Fig A3.13. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SDcra) for 0.3 sec period of structures with 5% damping for 475 years return period

134

Elnashai and El Khoury

•'vx.••\-V-V-\; V

V:.

111

iml I l/ll

w*f/J

.'••••/.

*?m

-:f-:j.••'•-.••

f

34'

'•W:

m Fig A3.14. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SDcm) for 0.6 sec period of structures with 5% damping for 475 years return period

Earthquake Hazard in Lebanon

135

ilitiit

Fig A3.15. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SDcm) for 1.2 sec period of structures with 5% damping for 475 years return period

136

Elnashai and El Khoury

HSS::

::35i:

t:hkp

MEDITERRANEAN

> 4*1 J / /

Jiiiiiiiii// / / P y

]

jiM-:b;kV--4--:.

/ i

/ /

/ / |SpII|L/.-:^

/ / /

/ /

mf-.•••/•> -34

M? • < M

i

f

?

• // /

* ?

i /

/

/

/

/

/

-

••/••••--:-/••.-.•••••• ••

//f¥v

lib

7

^ |lll|l||j|i(fj.:

f:

i:35:;

fas

I:tWW:i -V-/•:

37 33

Fig A3.16. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SD c m ) for 2.0 sec period of structures with 5% damping for 475 years return period

Earthquake Hazard in Lebanon

137

•36;

;

M

"-m

HSSH

MEDITERRANEAN •M^M

/ I

V //4 T

W&

J //

iNanit /

/

it

iPipi • 0 S 5 I

;

34

t

/

/.

/

so

// p

/ / *Qknascu£ :-/.;•;,-

A

' / / / / /

/

wmmf:;:. : 37:

:i3§;;

88

#:

.33.-^.;:

Fig A3.17. Uniform Hazard map of Lebanon in terms of Spectral Acceleration (S Ag) for 0.1 sec period of structure with 5% damping for 1000 years return period

Elnashai and El Khoury

138

17-7773>%?t

MfMli

m:\

:

::gS::

iMEDffiERRftNJEftN^

mm

f i <*

HLt

A 7 /i f f/ / /

// i:34>

/

/ 1

7/ lip /,* W////ill J rmiiy/.

-77

u/// 7,

7/J)/. • 7///Y /

/.- /' 1177/ ••il I (

||j^NC#/

"?:•• • - • • • : . # ' . ' • /

/ / / //

/:

/

/

•."-.

.-••••/•

,/:

/ / D&masofus

////

/y

:;3S!:

"47. ft&

#:4;;r7

•33

Fig A3.18.Uniform Hazard map of Lebanon in terms of Spectral Acceleration (SAg) for 0.3 sec period of structures with 5% damping for 1000 years return period

Earthquake Hazard in Lebanon

H3§:!

tm\ MEDITERRANEAN

139

yymmvn IliS

m

II m •I

Tripoli

• /

lip ,.B||,... .

/

,

-

•-

•

•

:

mm.: j :;34:=

'34

m

Jeirut '<% fSayda

LEBANON-

O

Damascus

MiMmifflm :

liSSi!

Plfc

37

33

Fig A3.19.Uniform Hazard map of Lebanon in terms of Spectral Acceleration (SAg) for 0.6 sec period of structures with 5% damping for 1000 years return period

140

Elnashai and El Khoury

tm 1:315:;

MEDITERRANEAN

i^ir

i!3S:;

Fig A3.20.Uniform Hazard map of Lebanon in terms of Spectral Acceleration (S Ag) for 1.2 sec period of structures with 5% damping for 1000 years return period

141

Earthquake Hazard in Lebanon

MEDITERRANEAN

}

Fig A3.21 .Uniform Hazard map of Lebanon in terms of Spectral Acceleration (SAg) for 2.0 sec period of structures with 5% damping for 1000 years return period

142

Elnashai and El Khoury

mmm wmm

m:,'\://:

*3§i:

m\

•^r:

iMlDITiEftRAMEANi:

?n:

mm/

0p#

iiiiiiiiiiiiiiiiiiiiiiiiiiiii^iii :

:

•

:

•

:

-

:

:

:

;

:

•

:

-

:

•

:

•

;

:

:

•

•.

•

y

: • _ : • _ : •

y - :

•;,

mmmmmzm •.••:•:••.••.-•.•:•:••:••.•.•/-:•:••-••/-•.-:-t

iiiiiiilili:

••34.

m

0B

J Bei

:::::;:-:':^: :;:;:;if; :;:;::#::;;;: :^:;;::;

••

^

/ •••./ y v . J ?

i:i;;i;i; jfsayda ' v

/ 1 •'/•'•

•••/

./...••

mMil: ISCUS;

!;|^:!;;;i;!;

jJiEBANON !:3S;;

r33:

.J

/

?

:37V ••33"

Fig A3.22. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SDcm) for 0.1 sec period of structures with 5% damping for 1000 years return period

Earthquake Hazard in Lebanon

143

SS:i

:i35i:

MEDITERRANEAN

1II//1 is /M4 1 /flmiwi m/ m*

f^j//////mf^:•->

m y / #/

/ / / / fM///v

/ / / / / / /

//jf.-'-J-•: ;/;

//F$/////

/

' ' /

y / / y/ /

/

Cj /

• / iALAJrV

/••• /

/ •>••/

~

=34

.

•••/•••

ffrrr&j&J / /. ' ////// / / fffn'ffg p ^ / / / / / iftij/f?$ / II mfy&i/f ///LAV/'J $

:3Si:

• '

*l'../' : -f

37

••"/••

33

Fig A3.23. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SDcm) for 0.3 sec period of structures with 5% damping for 1000 years return period

144

Elnashai and El Khoury

-35 35

MEDITERRANEAN

34 =

•Saydi r

LEBANON

35

Fig A3.24. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SDcm ) for 0.6 sec period of structures with 5% damping for 1000 years return period

Earthquake Hazard in Lebanon

r

145

35

35

MEDITERRANEAN

34 =

35

Fig A3.25. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SDcm) for 1.2 sec period of structures with 5% damping for 1000 years return period

146

Elnashai and El Khoury

mm m

^M4P/r\-m

±m\ :35;:

4.v.\;

IIUII

\ ••

it:

* V

mmmMmrntm

\

,1/1111 ti i /////&///mfc,:t. / / / / / ^

^M'

f

*////jwr•/•••:•.

/ / /

i f f

>

fjTr

••••/•

-34

// / 7'JY mmmf/ ••'•••'••'•••'••/.••'••'•••( t

/////] /

iiiSilll/ f/// r

/

J

/

I

/ # / / I

I

f [///

fVL

f

/ /

/

/

•/•• i

!••

/ . ...

i »/|

;SS;i

!,< f33

•136 I-1

37 33-^

Fig A3.26. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SD cm ) for 2.0 sec period of structures with 5% damping for 1000 years return period

Earthquake Hazard in Lebanon

147

Fig A3.27. Uniform Hazard map of Lebanon in terms of Spectral Acceleration (SAg) for 0.1 sec period of structure with 5% damping for 2500 years return period

Elnashai and El Khoury

148

-35

35

MEDITERRANEAN

34 s

35

Fig A3.28. Uniform Hazard map of Lebanon in terms of Spectral Acceleration (SAg) for 0.3 sec period of structures with 5% damping for 2500 years return period

Earthquake Hazard in Lebanon

149

MEDITERRANEAN

Fig A3.29. Uniform Hazard map of Lebanon in terms of Spectral Acceleration (S Ag) for 0.6 sec period of structures with 5% damping for 2500 years return period

150

Elnashai and El Khoury

Ml

?m\

MEDITERRANEAN

•m

'mm.

/ /

//

/

/ Damascus •:••; /

/

/

I /SfRIA

hSSii

m ; / " • •

'••

:iS

U

Fig A3.30. Uniform Hazard map of Lebanon in terms of Spectral Acceleration (SAg) for 1.2 sec period of structures with 5% damping for 2500 years return period

Earthquake Hazard in Lebanon

151

m\

M

W?*r*\:

m\

• $T<

MEMmfimM/m '

•

'

:

:

-

:

•

•

.

/

•

•

Fripqji > / & • : / . "

v

Wm

/ r

/

/

/ /

^

/ / / 111*,/ /, «* / <

/ '76i«&

1

^

:.h^M: :/:,

//.*/,

/

*T/J9 / /

wm//f / / ,/f /

1

ff!^pjji;:

7#y / /// < / Damascus

a

#

SYRIA 37

i:3Sii

36 Fig A3.31. Uniform Hazard map of Lebanon in terms of Spectral Acceleration (S Ag) for 2.0 sec period of structures with 5% damping for 2500 years return period

152

Elnashai and El Khoury

35

MEDITERRANEAN

34 a

'Sayd

'/

.EBANON

/ /

jJamasj&ts /

' f

RIA 37

35 36

33

J

Fig A3.32. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SDcm) for 0.1 sec period of structures with 5% damping for 2500 years return period

Earthquake Hazard in Lebanon

31

153

25::

;:35;;!

MEDITERRANEAN

•:34!?

LEBAN

;:35i:

Fig A3.33. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SDcm) for 0.3 sec period of structures with 5% damping for 2500 years return period

154

Elnashai and El Khoury

m

m^ H3K;

\mWMmmtiEm[ Mmf

, ///mm/?i l l / P( f////fw///\ 34

Mr

ffiiWfL?/

4

f /Damascus.-...-

^mlfff//--/ i

i L

n i l

iiBSh

;I

:

i

;

?

37

"••

33

Fig A3.34. Unifomi Hazard map of Lebanon in terms of Spectral Displacements (SDcm) for 0.6 sec period of structures with 5% damping for 2500 years return period

Earthquake Hazard in Lebanon

155

^MEDITERRANEAN;

Fig A3.35. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SDcm) for 1.2 sec period of structures with 5% damping for 475 years return period

156

Elnashai and El Khoury

35 35

MEDITERRANEAN

34"

/ 1

'Sayda .

/

/ <W

SYR FA 37

35 35

33

J

Fig A3.36. Uniform Hazard map of Lebanon in terms of Spectral Displacements (SD c m ) for 2.0 sec period of structures with 5% damping for 2500 years return period

References

Abe, K. (1981) "Magnitudes of large shallow earthquakes from 1904 to 1980", Phys. Earth & Plan. Inter., vol.27, pp.72-92. Abe, K. (1988) "Magnitudes and origin times from Milne seismograph data: earthquakes in China and California, 1898 -1912", ed. W. Lee, H. Meyers and K.Shimizaki, Historical Seismograms and Earthquakes of the World, pp.37-50, Academic Press. Abe, K. (1994) "Instrumental magnitudes of historical earthquakes 1892 to 1898", Bulletin of the Seismological Society of America, vol.84, pp.415425. Abe, K., Noguchi S. (1983a) "Determination of magnitude for large shallow earthquakes 1898 - 1917", Phys. Earth & Plan. Inter., vol.32, pp.45-59. Abe, K., Noguch S. (1983b) "Revision of magnitudes of large shallow earthquakes 1897-1912", Phys. Earth & Plan. Inter., vol.33, pp.1-11. Ambraseys, N. (1992) "Reappraisal of the seismic activity in Cyprus 1894 -1991", Bollet. Geofis. Teor. Appl., vol.34, pp. 41-80. Ambraseys, N. (1995) "The prediction of earthquake peak ground acceleration in Europe", Earthquake Engineering and Structural Dynamics, Vol.24, pp.467-490. Ambraseys, N. (1995a) "Magnitudes of Central American earthquakes 1898 - 1930", Geophys. Journ. Int., vol.121, pp.545-556. Ambraseys, N. (1995£>): "The prediction of earthquake peak ground acceleration in Europe". Earthquake Engineering and Structural Dynamics, 24, 467-490. 157

158

References

Ambraseys, N. (1997) "The earthquake of 1 January 1837 in southern Lebanon and northern Israel", Ann. Geofis., vol.40, pp.923-935. Ambraseys, N. (2000) "Reassessment of earthquakes, 1900 to 1999 in the Eastern Mediterranean and the Middle East", Geophys. J. Intern., vol. 141 (forthcoming). Ambraseys, N. and Adams R. (1996) "Large magnitude Central American earthquakes 1898-1994", Geophys. J. Intern., vol. 127, pp.665-692. Ambraseys, N. and Barazangi, M., (1989) "The 1759 earthquake in the Bekaa valley", /. Geophys. Res., 94, 4007-4013. Ambraseys, N. and Bommer, J. (1991) "The attenuation of ground accelerations in Europe". Earthquake Engineering and Structural Dynamics, vol.20, pp.1179-1202. Ambraseys, N. and Douglas, J. (1999) "Determination of station corrections from earthquakes in the Middle East", ESEE Re. 99-1, Imperial College of Sci., London. Ambraseys, N. and Douglas, J. (2000) "Reappraisal of surface-wave magnitude in the Eastern Mediterranean and the Middle East", Geophys. J. Internl, vol.141, pp.357-373. Ambraseys, N. and Finkel, C. (1987) "Seismicity of Turkey and neighbouring regions 1899 - 1915", Ann. Gephysicae, vol. 5B, pp.701-726. Ambraseys, N. and Free, M. (1997) "Surface-wave magnitude calibration for European region earthquakes", J. Earthq. Eng., vol. 1, pp. 1 -22. Ambraseys, N. and Jackson, J. (1998) "Faulting associated with historical and recent earthquakes in the Eastern Mediterranan region", Geophys.J. Mf., vol. 133, pp.390-406.

References

159

Ambraseys, N. and Karcz, I. (1992) "The earthquake of 1546 in the Holy Land", Terra Nova, vol.4, pp.253-262. Ambraseys, N. and Melville, C. (1982) A history of Persian earthquakes, Cambridge Univ. Press. Ambraseys, N. and Melville, C , (1988). An analysis of the eastern Mediterranean earthquake of 20 May 1202,. In: Historical seismograms and earthquakes of the world, ed. W. Lee, Academic Press, San Diego, 181-200. Ambraseys, N. and Melville, C. (1989) "Evidence for intraplate earthquakes in northwest Arabia", Bull. Seism. Soc. Am., vol.79, pp. 12791281. Ambraseys, N. and Melville, C. (1995) "Historical evidence of faulting in eastern Anatolia and northern Syria", Ann. Geofis., vol.38, pp.337-343. Ambraseys, N. and Sarma, S. (1999) "The assessment of total seismic moment", /. Earthq. Eng., vol.3, pp.439-461. Ambraseys, N., Simpson, K. and Bommer J. (1996) "Prediction of horizontal response spectra in Europe", Earthquake Engineering and Structural Dynamics, 25, 371-400. Amiran, D.H.K., Arieh, E. and Turcotte, T. (1990) "Earthquakes in Israel and adjacent areas: macroseismic observations since 100 B.C.E.". Anderson, J.G., Brune, J.N. (1999) "Probabilistic seismic hazard analysis without the ergodic assumption", Seismological Research Letters, 70, 1928. Annales de l'Observatoire de Ksara (1926-30). Arad V., Bartov Y., Weiler Y. (1998) "Seismicity and earthquakes in Israel: Bibliography", pub. GSI/16/98 Geol. Survey of Israel, Jerusalem.

160

References

Arieh E. (1967) "Seismicity of Israel and adjacent areas", Bull. Geol. Surv. Israel, no.43, pp. 1-14. Arieh E., Artzi D., et al. (1985) "Revised and updated catalogue of earthquakes in Israel and adjacent areas 1900 -1980", Pub. Z6/1216/83(3) Inst. Petrol. Res. and Geophys., Holon. Avni, R. (1999) "The 1927 Jericho earthquake", Ph.D. Thesis (2 vols), BenGurion Univ. of the Negev, Beer-Sheva. BAAS (1898) British Association for the Advancement of Science, Seismological Investigations, pp.204-207. BAAS (1912) British Association for the Advancement of Science, Seismological Investigations, 16th Report (1911) pp.26-36, 17th Report (1912) pp.2-22, 18th Report (1913), pp.2-7. Bath M. (1969) Handbook on earthquake magnitude determination, VESIAC Spec. Rep. 7885-36-X, Seism. Inst., 158pp., Uppsala. Bazzurro, Cornell, C.A. (1999) "Disaggregation of seismic hazard", Bulletin of the Seismological Society of America, 89, 501-520. Ben-Menahem A. (1979) "Earthquake cotalogue for the Middle East 92 BC - 1980 AD", Bull.Geophys. Teor, Appl, vol. 21, pp.245-313. Ben-Menahem A., Vered M., Brooke D. (1982) "Earthquake risk in the Holy Land", Boll. Geophys. Teor. Applic, vol.24, pp.175-203. Ben-Menahem A., Nur A., Vered M. (1976) "Tectonics, seismicity and structure of the Afro-Eurasian junction: the breaking of an incoherent plate", /. Phys. Earth and Plan. Inter., vo. 12 pp. 1-50.

References

161

Ben-Menahem A. (1991) "Four thousand years of seismicity along the Dead Sea Rift", J. Geoph. Res., vol.96, pp.20195-20216. Beydoun Z. (1977) "The Levantine countries: The geology of Syria and Lebanon" The Ocean Basins and Margins, vol.4A, The Eastern Mediterranean, ed. A. Naitn, pp.319-353, Plenum. Bommer, J.J., and Elnashai, A.S. (1999) "Displacement Spectra for seismic design", Journal Earthquake Engineering, Vol.3, No.l, pp. 1-32. Bommer, J.J., Elnashai, A.S., Chlimintzas, C , and Lee, D. (1998) Engineering Seismology and Earthquake Engineering Report ref. ESEE Report No. 98-3, Imperial College. Bommer, J.J., Martinez-Pereira (2000) "Strong-motion parameters: definition, usefulness and predictability", Proceedings of Twelfth World Conference on Earthquake Engineering, Auckland, paper no. 0206. Bommer, J.J., Scott, S.G., Sarma, S.K. (2000) "Hazard-consistent earthquake scenarios", Soil Dynamics & Earthquake Engineering, vol.19, no.4, pp.219-231. Butler, R.W.H., Spencer, S. and Griffiths, H.M., (1997). "Transcurrent fault activity on the Dead Sea transform in Lebanon and its implications for plate tectonics and seismic hazard", J. Geol. Soc. Lond., 154,757-760. Butler, R.W.H., Spencer, S. and Griffiths, H.M. (1998) The structural response to evolving plate kinematics during transpression: evolution of the Lebanese restraining bend of the Dead Sea transform. In: Continental Transpressional and Transtensional Tectonics, eds. Holdsworth, R.E., Strachan, R.A. and Dewey, J.F., Spec. Publ. Geol. Soc. Lond., 135, 81-106.

162

References

Cancani, A. (1897) "I pendoli orizontali del R. Osservatorio geodinamico di Rocca di Papa ed il terremoto indiano del 12 giunio 1897", Boll. Soc. Sism. Ital, vol.3, pp.235-240. Chaimov, T.A., Barazangi, M., Al-Saad, D., Sawaf, T. and Gebran, A. (1990) "Balanced cross sections and shortening in the Palmyride fold belt of Syria and implications for movement along the Dead Sea fault system", Tectonics, 9, 1369-1386. Chaimov, T.A., Barazangi, M., Al-Saad, D., Sawaf, T. and Gebran, A. (1992) "Mesozoic and Cenozoic deformation inferred from seismic stratigraphy in the southwestern intracontinental Palmyride fold-thrust belt, Syria", Gel. Soc. Am. Bull., 104, 704-715. Chapman, M.C. (1995) "A probabilistic approach to ground-motion selection for engineering design", Bulletin of the Seismological Society of America, 85, 937-942. Christensen A., Ziemendorff G. (1909) "Les tremblements de terre ressentis pendant l'annee 1905", Publ. Bureau Centr. Assoc. Intern. Sismolog., Serie B., pp.121-128, Strasbourg. Christoskov L., Kondorskaya N., Vanek J. (1983) "Earthquake magnitude in seismological practice, PH, S and L waves" Rada Matematickych a Prirodnich Ved, vol.93, no.l. 114 pp. Prague. Cornell, C. A. (1968) "Engineering seismic risk analysis", Bull. Seis. Soc. of America, vol.58, no.5, pp.1583-1606. DeMets, C , Gordon, R.G., Argus, D.F. and Stein S. (1994) "Effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions", Geophys. Res. Letts., 21,2191-2194. Dewey, J.F., Hempton, MR., Kidd, W.S.F., Saroglu, F. and Sengor, A.M.C. (1986) Shortening of continental lithosphere: the neotectonics of eastern

References

163

Anatolia - a young collision zone. In: Collision Tectonics, ed. M.P. Coward, A.C. Ries. Geol. Soc. Lond. Spec. Pubi, 19, 3-36. Duda S. (1965) "Secular seismic energy release in the circum-Pacific belt", Tectonoph., vol.2, pp.409-452. Ekstrom G. (1987) "A broad band method of earthquakes analysis", Ph. D. Thesis, Harvard Univ., Cambridge Mass., 216 pp. Ekstrom G., Dziewonski A. (1988) "Evidence of bias in estimations of earthquake size", Nature, vol.332, pp.319-323. Engdahl R., Hilst R. van der, Buland R. (1998) "Global teleseismic earthquake relocation with improved travel times and procedures for depth determination", Bull. Seism. Soc. Am., vol. 88, pp.722 - 743. Evernden J. (1971) "Variation of Rayleigh-wave amplitude with distance", Bull. Seism. Soc. Am., vol.61, pp.231-240. Garfunkel, Z., Zak, I. and Freund, R., (1981) "Active faulting in the Dead Sea Rift", Tectonophysics, vol.80, pp. 1-26. Gitterman, Y., Zaslavsky, Y. and Shapira, A. (1994) "Analysis of strong motion records in Israel", Earthquake Engineering, Rutenberg (ed), Balkema, Rotterdam. (Proc. 7th Regional European Seminar on Earthquake Engineering, Haifa, Israel, September, 1993). Gutenberg, B. (1945) "Amplitudes of surface waves and magnitude of shallow earthquakes", Bull. Seism. Soc. Am., vol.35, pp.3-12. Gutenberg, B (1956) "Great earthquakes 1896-1903", Trans. Am. Geophys. Un., vol.37,pp.608-614. Gutenberg, B. and Richter C. (1936) "Magnitude and energy of earthquakes", Science, vol.83, pp.183-185.

164

References

Gutenberg B., Richter C. (1954) Seismicity of the Earth and associated phenomena, 2nd Ed. Hanks Th., Kanamori H. (1979) "A moment magnitude scale", J. Geophys. Res., vol.84, pp. 2348-2350. Harajli, M.H. (1994) Seismic hazard assessment of Lebanon: zonation maps and structural seismic design regulations, Directorate of Urbanism, Beirut. Herak M., Herak D. (1993) "Distance dependence of Ms and calibrating function for 20 second Rayleigh waves", Bull. Seism. Soc. Am., vol.83, pp.1881-1892. Herak H., Panza G., Costa G. (1999) "Theoretical and observed depth correction for M s ", PAGEOPH, (In press). IASPEI (1967) "Recommendations of the committee on magnitudes", Comptes Rendus, vol.15, p.65. Jackson, J., (1994) "Active tectonics of the Aegean region", Ann. Rev. Earth Planet. Sci., 22, 239-271. Jackson, J., McKenzie, D. (1984) "Active tectonics of the Alpine Himalayan Belt between western Turkey and Pakistan", Geophys. J. R. astr. Soc, vol.77, pp. 185-264 Jackson, J.A. and McKenzie, D. (1988) "The relationship between plate motions and seismic moment tensors and the rates of active deformation in the Mediterranean and the Middle East", Geophys. J. Roy. Astr. Soc, 93, 45-73. Jestin, F., Huchon, P. and Gaulier, J.M. (1994) "The Somalia plate and the East African Rift system: present day kinematics", Geophys, J. Int., 116,637-654.

References

165

Joffe, S. and Garfunkel, Z. (1987) "Plate kinematics of the circum Red Sea: are-evaluation", Tectonophysics, 141, 5-22. Johnston, A. (1996a) "Seismic moment assessment of earthquakes in stable continental regions I. Instrumental seismicity", Geophys. J. Int. vol.124, pp.381-414 Johnston, A. (1996b) "Seismic moment assessment of earthquakes in stable continental regions II. Historical seismicity", Geophys. J .Int. vol.124, pp.639-678. Joyner, W.B. and Boore, D.M. (1981) "Peak horizontal acceleration and velocity from strong motion records including records from the 1979 Imperial Valley, California earthquake", Bulletin of the Seismological Society of America, vol.71, pp.2011-2038. Kallner-Amiran, D. (1951-52) "A revised earthquake catalogue of Palestinine", Israel Explor. Journ., vol.1, pp.223-246, & vol.2, pp.48-65, Jerusalem. Kanamori, H. (1977) "The energy release in great earthquakes", J. Geophys. fles., vol.82, pp. 2981-1987. Kanamori, H., Abe, K. (1979) "Re-evaluation of the turn-of-the-century seismicity peak", /. Geophys. Res., vol.84, pp.6131-6139. Karnik, V. (1968) Seismicity of the European area, D. Reidel, Dordrecht Karnik, V. (1977) "Comparison of empirical A/T curves in near epicentral distances", Publ. Inst. Geoph. Polish Acad. ScL, vol.A5, pp.61-64, Warsaw. Karnik, V. (1996) Seismicity of Europe and the Mediterranean, Praha. Karnik, V., et al. (1962) "Standardisation of the earthquake magnitude scale", Studia Geoph. et Geodet., vol.6, pp.41-47.

166

References

Karnik, V., Christokov L. (1977) "Magnitude determination at short epicentral distances in Europe", Publ. Inst. Geoph. Polish Acad. Sci., vol.A5, pp.51-60, Warsaw. Kortazzi, J. (1900) "Les perturbations du pendule horizontal a Nicolajew en 1897, 1898 et 1899", Gerl;. Beitr. Geophys., vol.4, 383-405. Kovach, R. (1988) "Earthquake hazard in Jordan", Natural Hazards, vol.1, pp.245-254. Kovach, R., Andersen, G., Gettings, M., Healy, J. (1986) "Seismicity of western Jordan", Open File Rep. 86-561, U.S. Geol. Survey, Menlo Park. KSA Bulletin Seismique, Observatoire de Ksara (1911, 1913-1969). Kramer, S.L. (1996) Geotechnical Earthquake Engineering. Prentice-Hall. Krinitzsky, E.L. (1998) The hazard in using probabilistic seismic hazard analysis for critical structures. In: Geotechnical Engineering & Soil Dynamics III, Dakoulas, Yougian & Holtz eds., ASCE Geotechnical Special Publication No. 75, vol.1, 164-165. Le Pichon, X. and Gaulier, J.M. (1988) "The rotation of Arabia and the Levant fault system", Tectonophysics, 153, 271-294. Lienkaemper, J. (1984) "Comparison of two surface-wave magnitude scales: M of Gutenberg and Richter (1954) and Ms of Preliminary Determination of Epicentres", Bull. Seism. Soc. Am. vol.74, pp.2357 - 2378. Lyberis, N., Yurur, T., Chorowicz, J., Kasapoglu, E, Gundogdu, N. (1992) "The East Anatolian Fault: an oblique collisional belt", Tectonophysics, 204, 1-15. McBride, J.H., Barazangi, M., Best, J., Al-Saad, D., Sawaf, T., Al-Otri, M. and Gebran, A. (1990) "Seismic reflection structure of intracratonic

References

167

Palmyride fold-thrust belt and surrounding Arabian platform", Am. Assoc. Petrol. Geol. Bull, 74, 238-259. McClusky, S. et al (28 authors) (2000) "GPS constraints on plate motions and deformations in the eastern Mediterranean: implications for plate dynamics", J. Geophys. Res., 105, 5695-5719. McGuire, R. (1976) "Fortran computer program for seismic risk analysis", US Geological Survey Open-File Report 76-67. McKenzie, D. (1970) "The plate tectonics of the Mediterranean region", Nature, 226, 239-243. McGuire, R.K. (1995) "Probabilistic seismic hazard analysis and design earthquakes: closing the loop", Bulletin of the Seismological Society of America, 85, 1275-1284. McKenzie, D. (1976) "The East Anatolian fault: A major structure in eastern Turkey", Earth Plan. Sci. Lett., vol.29, pp.189-193. Makropoulos, K.C. and Burton, P.W. (1986) "HAZAN, A fortran program to evaluate seismic hazard parameters using Gumbel's theory of extreme value statistics", Computers and Geosciences, vol.12, pp.29-46. Marshall, P., Basham, P. (1973) "Rayleigh wave magnitude scale Ms", Pure &Appl. Geophys., vol.103, pp.406-414 Mohamad, R., Darkal, A.N. et al. (2000) "Remote earthquake triggering along the Dead Sea fault in Syria following the 1996 Gulf of Aqaba earthquake", Seism Res. Letters, vol.71, pp.47-52. Mount, V.S. and Suppe, J., (1987). "State of stress near the San Andreas fault: implications for wrench tectonics" Geology, 15,1143-1146. Nuttli, O. (1973) "Seismic waves attenuation and magnitude relations for Eastern North America", /. Geophys. Res., vol.78, pp.876-885.

168

References

Panza, G., Duda, S., Herak, M. (1989) "Gutenberg's surface wave magnitude calibrating function: theoretical basis from synthetic seismograms", Tectonophys., vol. 166, pp.35-43. Papazoglou, A.J., Elnashai, A.S. (1996) "Analytical and field evidence for the damaging effect of vertical earthquake ground motion", Earthquake Engineering & Structural Dynamics, 25, 1109-137. Perez, O. (1999) "Revised world seismicity catalogue 1950 - 1997 for strong Ms > 6 shallow h<70 earthquakes", Bull. Seism. Soc. Am., vol.89, pp.335-341. Plassard, J., Kagoj, B. (1981) "Seismicite du Liban", Mem. Observ. Ksara, vol.4, pp. 1-47, pub. Canseil Natl. Researche Sci., Beyrouth . Quennell, A. (1958) "The structural and geomorphic evolution of the Dead Sea rift", Q. J. Geol. Soc. London, vol. 114, pp.1-24. Quennell, A. (1984) The western Arabia rift system, in The Geological Evolution of the Eastern Mediterranean, ed. J. Dixon and A. Robertson, vol.17, pp.775-788. Rebeur-Paschwitz, E. (1893) "Ueber die Aufzeichnung der Fernewirkung von Erdbeben", Peterm. Geogr. Mitteii, no.19, pp.201-212. Rebeur-Paschwitz, E. (1895) "Horizontalpendel-Beobachtungen auf der Kaiserlichen Universitats Sternwarte zu Strassburg 1892-1894", Beitr. z. Geophys., vol.2, pp.452-454. Reiter, L. (1990) Earthquake Hazard Analysis: Issues and Insights. Columbia University Press. Rezapour, M., Pearce, R. (1998) "Bias in surface-wave magnitude Ms due to inadequate distance correction", Bull. Seism. Soc. Am., vol.88, pp.43-61.

References

169

Richter, C. (1935) "An instrumental earthquake magnitude scale", Bull. Seism. Soc. Am., vol.25, pp. 1 -32. Richter, C. (1958) Elementary seismology, p.351, W. Freeman. Ron, H., Freund, R., Garfunkel, Z. and Nur, A., (1984) "Block rotation by strike-slip faulting: structural and paleomagnetic evidence", J. Geophys. Res., 89, 6256-6270. Rosenthal, E. (1907) "Katalog der im Jahre 1904 registrierten seismischen Storungen", Publ. Bureau Centr. Assoc. Intern. Seism., Strassburg. Rothe, J. (1989) "The seismicity of the earth 1953-1965", Publ. Earth Sci. Dept., UNESCO, Paris. Rotstein, Y. (1983) "Tectonic investigations in the eastern Mediterranean region", Rep. Inst.Petrol. Res. and Geophys., Holon. Rudolf, E. (1905) "Katalog der im Jahre 1903 bekannt gewordenen Erdbeben", Keis. Hauptst. f. Erdbebenfor. Strassburg, 673pp., Leipzig. Salamon, A. (1993) Seismotectonic analysis of earthquakes in Israel and adjacent areas, Ph.D. Thesis, Hebrew Univ. Jerusalem. Salamon, A., Hofstetter, A., Garfunkel, Z., Ron, H. (1996) "Seismicity of the eastern Mediterranean region: perspective from the Sinai subplate", Tectonophys., vol. 263, pp.293-305. Seismological Bulletins of the Seismological division of the Inst, for Petrol, research and Geophys., Sep.1981 onwards. Scholz, C.H., Aviles, C. and Wesnousky, S, (1986) "Scaling differences between large intraplate and interplate earthquakes", Bull. Seism. Soc. Am., 76, 65-70.

170

References

Seggern, D von (1977) "Amplitude-distance relation for 20-second Rayleigh waves", Bull. Seism. Soc. Am., vol.67, pp.405-411. Shide Circulars Nos 1 to 27, British Assoc. Adv. Sci. 1899-1912. Sieberg, A. (1917) "Catalogue des tremblements de terre ressentis pendant l'anne 1908", Publ. Bureau Centr. Assoc. Intern. Sism.. p.88. Strasbourg. Sieberg, A. (1932) "Die Ergbeben", Leipzig. Soloviev, S.L. (1955) "O klassifikatsii zemletrasenii po velichine ikh energii", Trudi Geofiz. Inst. Akad. NaukSSSR, no.30 (157) pp.3-31 Soloviev, S. L. (1961) "Magnituda zemletriasenii", ed. Savarenski E., Zemletriasenia v CCCP, pp.91-100. Soloviev, S. L., Shebalin, N. (1957) "Opredelenie intensivnosti zemletriasenii po smeshchenia pochvi v poverkhnostikh volnakh", Ser. Geofis. Izvest. Aka. Nauk no.7. Somerville, P.G., Smith, N.F., Graves, R.W., Abrahamson, N.A. (1997) "Modification of empirical strong ground motion attenuation relations to include the amplitude and directivity effects of rupture directivity", Seismological Research Letters, 68, 199-222. Stepp, J.C. (1971) "An investigation of earthquake risk in the Puget Sound area by use of the type 1 distribution of largest extremes", Pennsylvania State Univ, Ph.D. Thesis in Geophysics. Striem, H.L. (1986) "Macroseismic effects in Israel due to earthquakes in the ninteenfifties", Rep. Zl/567/79(43) Imst. Petrol. Research and Geophys., Holon. Szirtes, S. (1909) "Katalogue der im Jahre 1905 registrierten seismichen Storungen", Publ. Bur. Centr. Assoc. Intern. Sism., Serie A., pp.13-14, Strassburg.

References

171

al-Tarazi, E. (1992) "Investigation and assessment of seismic hazard of Jordan and its vicinity", Doct. Dissert., Ruhur-Univers. Bochum. Vanek, J. et al. (1962) "Standardisation of magnitude scales", Bull. (Izvest.) Acad. Sci. USSR, Geophys. Ser., no.2, pp.108-111. Vanek, J. (1995) 'Comment on "Distance dependence of Ms calibration function for 20 second Rayleigh waves" by M. Herak and D. Herak', Bull. Seism. Soc. Am., vol.85, pp.961. Walley, CD. (1988) "A braided strike-slip model for the northern continuation of the Dead Sea fault and its implications for Levantite tectonics", Tectonophys., vol. 145, pp.63-72. Willmore, P. (1979) Manual of seismological observatory practice, Rep. SE-20, World Data Centre A Solid Earth Geoph., U.S. Dept. of Commerce. Yucemen, M.S. (1992) "Seismic hazard map for Jordan and vicinity", Natural Hazards, vol.6, pp.201-226.

his book presents a comprehensive treatment of earthquake hazards in Lebanon and its vicinity. A thorough review of the tectonics of the region is given alongside a re-assessment of the historical and instrumental earthquake records. Probabilistic seismic hazard analysis is undertaken and hazard maps are presented in terms of peak ground parameters as well as spectral ordinates (acceleration and displacement). Owing to their significance to the economy of Lebanon, the three cities of Beirut, Sidon and Tripoli are subjected to site specific earthquake hazard assessment. The maps provided are the best available estimates of seismic hazards in Lebanon and are recommended for use in risk assessment. Also, the basis and framework for similar studies in the Levant are given. The rigorous and pragmatic approach adopted by the authors renders the book accessible to design engineers and researchers alike.

P330 he ISBN 1-86094-461 -?

Imperial www.icpress.'

lieg Pi ss 781860"9*,4611