Introduction

Sinai is considered as a tectonic sub-plate with somedoubtful boundaries. The Gulf of Aqaba–Dead Seatransform system, together with the Mediterraneanmargin, the folded Syrian arc system and the Gulf ofSuez, may define the Sinai micro-plate (Eyal and Riches

1983). In 1969 and 1995 two large earthquakes occurredalong the northern Red Sea and the Gulf of Aqaba(magnitude 6.9 and 7.2, respectively), in addition tomany events with magnitudes greater than 5.

The increasing development and urbanization in Sinairequire a heightened sensitivity towards earthquakes andtheir potential impact on life and property. The Global

Bull Eng Geol Env (2006) 65: 309–319DOI 10.1007/s10064-006-0044-3 ORIGINAL PAPER

M. El-Hefnawy

A. Deif

S. T. El-Hemamy

N. M. Gomaa

Probabilistic assessment of earthquakehazard in Sinai in relation to the seismicityin the eastern Mediterranean region

Received: 26 November 2005Accepted: 8 February 2006Published online: 27 June 2006� Springer-Verlag 2006

Abstract Sinai is surrounded by themost active seismic trends in Egyptand earthquake risk reduction hasbecome an important ongoing socio-economic concern. Twenty-fiveearthquake source zones were usedto define the seismicity of the easternMediterranean region. Peak groundacceleration (PGA) values with a90% probability of not being ex-ceeded in 50 and 100 years weredetermined for the Sinai and DeadSea regions. These indicated thehighest relative levels of groundmotion are expected in regionsneighbouring the Gulf of Aqaba, theDead Sea and the southern part ofthe Gulf of Suez. Other regions werecharacterized as having a relativelylow to intermediate level of PGAvalues. The PGA values obtainedwill be useful for civil engineers,regulators and planners, in order tomitigate the effects of earthquakesand to plan earthquake resistantdesigns.

Keywords Seismic hazard Æ Probabi-listic Æ NPP Æ Dabaa

Resume Le Sinaı est entoure desplus actives zones sismiquesd’Egypte et la reduction du risquesismique represente une preoccupa-tion socio-economique actuelle.Vingt-cinq zones sources de trem-blements de terre ont conduit al’etablissement de la sismicite de laMediterranee orientale. Les accele-rations de pic au rocher avec uneprobabilite de non depassement de90% en 50 et 100 ans ont ete de-terminees pour les regions du Sinaıet de la Mer Morte. Les plus fortesvaleurs de mouvement au sol sontattendues dans les regions prochesdu Golfe d’Aqaba, la Mer Morte etla partie sud du Golfe de Suez.D’autres regions ont ete cara-cterisees avec des niveaux faibles oumoyens d’acceleration de pic. Cesvaleurs d’acceleration serviront auxingenieurs de genie civil et amenag-eurs, afin de concevoir des structuresresistant aux seismes et limiter leseffets des seismes.

Mots cles Alea sismique Æ MerMorte Æ Sinaı Æ Golfe de Suez

M. El-Hefnawy Æ N. M. GomaaEl-Azhar University, Cairo, Egypt

A. DeifNational Research Institute of Astronomyand Geophysics, Cairo, Egypt

S. T. El-Hemamy (&)Siting and Environmental Department,National Center for Nuclear Safetyand Radiation Control Ahmad El-Zomor,Nasr city, Cairo 1175, EgyptE-mail: ksoheir@yahoo.com

Seismic Hazard Assessment Program (GSHAP) high-lighted the assessment of seismic hazard as the first steptoward earthquake risk mitigation (Giardini 1999). Theseismic hazard assessment of the present study considersthe region that extends from 32� to 36� E and 27� to 32�N. Numerical calculations were undertaken utilizing theSEISRISK III routine developed by Bender and Perkins(1987). Uncertainties due to errors associated with thesource boundaries and attenuation model are taken intoconsideration.

The seismicity is based on the compiled catalogues ofhistorical seismicity of Ambraseys et al. (1994) andinstrumental seismicity. This instrumental seismicity isfrom the International Seismological Center (ISC),Papazachos and Papazachos (1997), the bulletins of theEgyptian National Seismological Network (ENSN),Bulletins of the National Research Institute of Astron-omy and Geophysics (NRIAG) and the seismologicalcatalog of Israel produced by the Institute of PetroleumResearch and Geophysics (IPRG). Uniformity in mag-nitude was obtained by converting all magnitudes tosurface wave magnitude.

Seismicity of Sinai and its surrounding area

Most of the seismic activity of Egypt and its surroundingarea is concentrated along the following three localnarrow belts: the Gulf of Aqaba–Dead Sea trend; theNorthern Red Sea–Gulf of Suez–Cairo–Alexandriatrend and the Mediterranean Coastal Dislocation trend.

The seismicity of the Aqaba–Dead Sea transform isconcentrated in the deep depressions occupied by theGulf of Aqaba and the Dead Sea. Little activity is ob-served along the Araba valley (Fig. 1) North of theCarmel–Fari’a fault system, the seismic activity is scat-tered on the western side of the transform. Further tothe north there is very little seismic activity along theYammouneh restraining bend and its northward con-tinuation. Although there are different focal mechanismsalong the transform system, the fault plane analyses ofthe major earthquakes confirm its left lateral nature(Salamon et al. 2003). Strong events, as well as most ofthe small ones, are concentrated in a belt which extendsalong the geologically defined borders and margins ofthe transform system. Some low to moderate activity isrecorded within the intraplate regions, mostly in thenorth.

The northern Red Sea–Gulf of Suez–Cairo–Alexan-dria trend extends from the Sinai triple junction north-west along the Gulf of Suez and continues to includethe main part of the Nile Delta to Alexandria (Fig. 2).It is the location of a number of historic reportedearthquakes that have assigned intensities higher thanVII (Poirier and Taher 1980; Maamoun et al. 1984;Ambraseys et al. 1994). Focal mechanism parameters

obtained for the earthquakes of Abu-Hammad (1974)and Alexandria (1955) and that which occurred in theNorthern Red Sea in March 1969 showed that theseevents have a left-lateral strike-slip component.

No large earthquakes are recorded in the middle partof the Gulf of Suez or between Cairo and Alexandria;only small earthquakes with doubtful locations. Theepicentral distribution of the earthquakes (Fig. 2) indi-cates a clustering of the events beneath the southern partof the Gulf of Suez. Focal mechanism analysis of theearthquakes in this cluster indicated almost entirelynormal faulting with planes strictly parallel or sub-par-allel to the axis of the Gulf (Daggett et al. 1986).

Earthquakes in the middle of the Gulf of Suez are oflower magnitude compared with those in the southernpart. The focal mechanism of the 1983 Shukeir earth-quake (magnitude 4.7) lies in the middle of the Gulf. Themovement indicates strike-slip faulting with a minornormal component. The earthquake occurred along theoblique structure and not along the marginal faults ofthe Gulf of Suez (Maamoun 1985). Focal mechanismanalyses show the movement between the earthquakes

Fig. 1 Seismicity and main tectonics of the Gulf of Aqaba–DeadSea transform (modified after Garfunkel et al. 1981; Klinger et al.2000; Salamon et al. 2003). Abbreviations of geological elementsand localities: ABV Araba valley, CF Carmel fault, FF Fari’a fault,GSZ Gulf of Suez, GAQ Gulf of Aqaba, HKD Hula and Kineretdepressions, JVF Jordan valley fault, NMTJ North Mediterraneantriple junction, RF Roum fault, SGL sea of Galilee, YMFYammuneh fault

310 M. El-Hefnawy et al.

occurred on the marginal and transverse faults (Fig. 3).Some of the earthquakes have a significant normalcomponent while others have strike-slip mechanisms. Tothe north of the Gulf of Suez the epicentral distributionis very diffuse and cannot be attributed to any of theknown faults. The fault plane analyses for the earth-quakes which have occurred in this area indicate almostnormal faulting (Fig. 3).

The area of Dahshour (south west of Cairo) and itssurrounds has experienced some historical earthquakesand a catastrophic event on October 12, 1992. Faults inthis area have two prominent trends: E–W (parallel tothe Mediterranean) and NW–SE (parallel to the Gulf ofSuez). The focal mechanism analysis indicates normalfaulting or normal faulting with a strike-slip component(Fig. 3).

Maamoun and Ibrahim (1978) defined the Mediter-ranean Coastal Dislocation Trend. They attributed itsactivity to the continental shelf and the probable deepfaults parallel to the coast. Being parallel to the conti-nental margin, it could be considered as a zone ofweakness zone which experienced thinning during theTriassic period (Ben Avraham et al. 1987). Unfortu-

nately this offshore area has limited earthquakerecording systems; thus the foci distribution is difficult todetermine.

Seismicity model

Earthquake catalogue

The revised earthquake catalogue for Sinai and its sur-rounds forms the basis of the present study. The subsetof the catalogue used for hazard calculation includesearthquakes with magnitude Ms ‡ 3.0 between 184 BC

and 2003 AD. All the available scales have been con-verted into Ms scale using a linear least square tech-nique.

Earthquake source zones

Seismic zones were determined from a consideration ofthe present-day tectonic regime, seismicity and thelocation of known faults. The regional seismicity ofconcern to Sinai was divided into 25 seismogenic zones

Fig. 2 Seismicity and main tectonics of Egypt and its surrounds(modified after the geologic map of the Egyptian Geological Surveyand Mining Authority 1981). Abbreviations of geological elementsand localities: GSZ Gulf of Suez, GAQ Gulf of Aqaba, HAG WadiHagoul

Fig. 3 Focal mechanisms available for Egypt and its surrounds.The white quadrants are for Up (first) motions while the infilledquadrants indicate Down ones. The numbers in the figure arearranged in an ascending order according to the date of theearthquake. The size of each ‘‘beach ball’’ is proportional to theearthquake magnitude

Probabilistic assessment of earthquake 311

including a background one. These zones were related tothe tectonic activity of the previously defined localseismicity belts. Historic and recent seismicity togetherwith the related phenomena show that Egypt is affectedby large earthquakes of intermediate depth in the Hel-lenic Arc (Papadopoulos 1987) and hence these are alsoincluded in the seismic hazard maps for Sinai. Parame-ters used for the probabilistic seismicity model are givenin Table 1.

Seismogenic zones of the Gulf of Aqaba–Dead Seatransform system

The seismogenic zones of this active trend are shown inFig. 4 and can be summarized as follow:

1. The Gulf of Aqaba (AQB) is a basin trendingnortheast southwest. It experienced the largestEgyptian earthquake with a magnitude of 7.2 inNovember 1995. The Gulf of Aqaba has been themost active seismic area over the last three decades,characterised by swarm activity. The variety of thefocal mechanism solutions reflects the complexity ofthe structure within the Gulf. Some mechanismsshow normal faulting and thus are attributed to thefaults that form the boundaries of the major basins inthe Gulf; others indicate left lateral motion of thetransform (Salamon et al. 2003).

2. The Araba valley (ARV) is an inter-basin zonetrending northeast southwest. The Araba Valleyfaults extend over 160 km from the Gulf of Aqaba tothe Dead Sea and provide morphological evidence ofessentially strike-slip motion (Klinger et al. 2000). Itis characterized by its low seismicity compared withthe surrounding area, despite clear indications of re-cent faulting (Gerson et al. 1993). Four historicearthquakes have been reported in the Araba Valleyin the last few thousand years. Estimated magnitudesestimated for these events would be slightly smallerthan the earthquake which struck the Gulf of Aqabain 1995. Klinger et al. (2000) emphasized the limitedearthquake activity in the Araba Valley over theinstrumental period. No focal mechanism analysesare available for this zone.

3. The Dead Sea Basin (DSB) trends almost northsouth. It is characterized by its double fault system(the ARV Fault from the east and the Jordan Faultfrom the west). Swarm and a main-shock/after-shocktype of earthquake activity characterize the Dead Seaseismogenic zone. South of the Carmel Fault, theseismogenic belt is narrow and the epicentres are

Fig. 4 Seismogenic sources of Aqaba–Dead Sea transform

Table 1 Parameters for the 25 seismogenic zones

Seismiczone

b Value a Value Maximummagnitude

AQB )0.81 3.96 7.6ARV )0.89 2.41 7.2DSB )0.96 3.27 7.4JVS )1.16 3.21 6.8HKB )0.85 2.49 7.2CIS )0.82 0.93 5.9CFF )0.85 2.83 6.9LMS )0.86 2.96 7.2GHB )0.99 2.92 7.4SGS )0.95 4.61 7.3MGS )1.24 4.13 5.5NGS )1.08 3.27 5.9CSD )0.63 2.39 5.5SWC )0.85 2.83 6.3EMZ )0.97 3.21 6.5CEM )0.83 2.62 7.0WEM )0.76 3.61 6.6HL1 )0.56 2.33 7.9HL2 )0.65 2.43 8.2HL3 )0.56 2.26 8.0HL4 )0.75 2.85 7.1HL5 )0.75 3.00 7.1HL6 )0.75 2.53 7.1CYS )0.67 2.79 7.6Background )0.97 4.12 6.1

312 M. El-Hefnawy et al.

concentrated in the deep depression of the Dead Sea.Based on surface wave data, Ben-Menahem et al.(1976) obtained focal mechanisms for the 1927earthquake showing left lateral motion on a sub-vertical fault striking N10�E, i.e. parallel to thetransform in this area. The normal mechanisms ofrelatively recent events (Salamon et al. 2003) seem toreflect the activity of the longitudinal N–S strikingnormal faults that extend along the margins of theDead Sea depression and cannot be related to theexpected lateral motion along the transform. Fieldobservations have confirmed the activity of thesefaults (Garfunkel et al. 1981; Gardosh et al. 1990).

4. The Jordan Valley seismogenic zone (JVS) trendsnorth south, linking the Hula basin in the north andthe DSB in the south. The details of its termination inthe Sea of Galilee are not clear from surface expres-sions (Ben-Menahem et al. 1976). Garfunkel et al.(1981) notes a small amount of compression near theJordan Fault trace. Earthquake activity along theJordan valley is low compared with the DSB to thesouth.

5. North of the Jordan Valley, the Hula and Kineretbasins (HKB) are present. Seismic activity in theHula and Kineret basins has been recorded up to thenortheast bend of the transform at the YammunehFault. Shamir et al. (2001) considered this area as aseismogenic step zone between the Roum Fault in thewest and the Jordan Fault in the east.

6. The undefined seismic activity running from thenorthern Dead Sea to the Mediterranean coastdelineates another seismogenic zone (CIS) which mayextend to offshore structures beneath the Mediterra-nean Sea.

7. The Carmel Fari’a active fault (CFF) extendsnorthwest from the lower Jordan Valley in thesoutheast to the Mediterranean coast. The presentmovement of the Carmel Fault is left lateral; itscentral segment being a restraining bend which causesthe uplift of the Carmel Mountain (Rotestein et al.1993; Hofstetter et al. 1996). As indicated in Fig. 1,the seismic activity toward the northwest coincideswith the Carmel Fari’a Fault.

8. The Lebanon mountain segment (LMS) is locatedwhere the rift changes its orientation towards thenortheast, such that the strike is not parallel to theoverall direction of the relevant plate motion. Themain rupture is the Yammouneh Fault, althoughlarge active faults which splay to the east and westmay also be important. The surface traces of thesesplay faults die out some 50–60 km to the north ofthe Jordan Valley (Garfunkel et al. 1981). Theseismicity along the Yammuneh bend is scattered,probably due to the complex deformation in a widearea around the main transform line. This defor-mation is due to sub-parallel faults (Dubertret

1955), block rotation (Ron 1984) and branchingfaults (Thenhause et al. 1993). As the strain is takenup by many secondary faults, the seismogenic beltis wide.

9. At the northern end of the Aqaba–Dead Sea riftsystem, the Ghab Fault (GHB) extends north–south(Fig. 3, Table 2). The seismicity around the Ghab islow, having been quiescent since the September 1918earthquake. The focal mechanism analysis of thatevent indicates a left lateral motion, parallel to thetransform (Ben-Menahem et al. 1976).

Seismogenic zones of the Northern Red Sea/Gulfof Suez/Cairo/Alexandria trend

The seismogenic zones of this active area are shown inFig. 5. Meshref (1990) suggested a model that separatesthe Gulf of Suez into three main tectonic provinces.From the direction and amount of downthrow of theblocks, he deduced that there is a southwest regional dipof the tilted fault blocks in both the northern andsouthern provinces. The central province has a northeastregional dip and is separated from the northern andsouthern provinces by two major accommodation zoneswith a relatively flatter dip. Based on this change of dip,the Gulf of Suez is divided into the Southern Gulf ofSuez (SGS), the Middle Gulf of Suez (MGS) and theNorthern Gulf of Suez (NGS). These zones can becharacterised as follows:

(a) The SGS has suffered intensive structural deforma-tion. The earthquakes are concentrated beneath thispart of the Gulf. A linear regression fault planeanalysis made of the projected foci onto a verticalplane indicated a fault plane parallel or sub-parallelto the Gulf axis (Daggett et al. 1986).

The focal mechanisms of the 1969 and 1972 earth-quakes which occurred in the southern part of the Gulfof Suez indicate normal faulting parallel to the Gulf axis(Jackson and McKenzie 1984). This is consistent withthe results obtained using the waveform inversion tech-niques proposed by Huang and Solomon (1987).

An estimated 15–20 km of crustal stretching in thesouthern part of the Gulf was accommodated throughfaulting and block tilting. However, crustal separationwas too small to result in the production of an oceaniclithosphere between the Sinai and Nubian plates (Gar-funkel and Bartov 1977). The amount of crustalstretching decreases northward along the rift.

(b) The MGS is characterized by its low activity com-pared with the southern part. Abu El-Enean (1997)conducted some focal mechanism analyses whichindicated strike-slip faulting with a normal compo-nent. This transformation, from a purely normal

Probabilistic assessment of earthquake 313

faulting in the Southern part to a mixed (strike-slipand normal) movement, together with the change ofseismic activity and direction of downthrow and thecrustal stretching, supports the separation betweenthe Southern and Middle seismogenic zones.

(c) The NGS is characterized by its low seismic activity.A unique large earthquake occurred in 742 with anintensity of VII. The fact that it has not been re-peated may be due to error in its location or its largereturn period. Focal mechanism analyses for thisseismogenic zone indicate normal faulting (Fig. 3).

(d) The Cairo-Suez district (CSD) is affected by threefault trends, one east–west and the other two ENEand NW (Abdel-Rahman and El-Etr 1978). Thefaults are predominantly normal and have produceda series of positive and negative fault blocks (Abdel-Rahman and El-Etr 1979) and a large strike-slipcomponent (Fig. 3). The first nodal plane trendsmainly ENE–WSW to E–W, parallel to the TethysSea, while the second trends NW–SE to NNW–SSE.

Field observations, landsat images, aerial photo-graphs and seismicity records confirm the active tecto-nism between Cairo and Suez. Active spots on this beltlie at Wadi Hagul and Abu Hammad. The epicentraldistribution is very diffuse and cannot be attributed toany of the known faults. This diffusion (Fig. 2) makes itdifficult to delineate other seismogenic zones hence thearea is considered as one. It is assumed that the seismicpotential is uniform throughout the zone, although thisis not entirely clear.

(e) The epicentral area of the 1992 Cairo earthquake isconsidered as a separate seismic zone (Abu El-Enean1997; Deif 1998) based upon the epicentral distri-bution, seismicity level and the similarity of focalmechanisms. This area (SWC) experienced somehistoric earthquakes prior to that on October 12,1992. The faults in this area trend E–W, parallel tothe Mediterranean, or NW–SE, parallel to the Gulfof Suez. The focal mechanism analyses indicatenormal faulting or normal faulting with a largestrike-slip component (Fig. 3). The E–W nodal planeis consistent with the surface traces which appeareddirectly after the 1992 event. Thus, this plane isconsidered to be the probable fault plane for themain-shock of the 1992 event.

Seismogenic zones of the Egyptian Mediterraneancoastal dislocation zone

The authors have divided this area into three seismo-genic zones, based mainly on the available focal mech-anism analyses and the clustering of the seismic activity.

The seismogenic zones of this active trend are shown inFig. 5 and can be summarized as follow:

1. A seismogenic zone parallels to the Eastern Medi-terranean coast (EMZ) with a NNE–SSW trend. Thisoffshore seismicity extends more than 100 km fromthe eastern Mediterranean coast, south of the CypriotArc. No information concerning the fault structure inthis area is available.

2. The Central Egyptian Mediterranean Coastal zone(CEM) lies in front of the Nile Delta and is affectedby the main tectonic activity which produced theshape of the Nile Delta offshore cone. The focalmechanism analysis of the 1955 Alexandria earth-quake (Fig. 3) indicates a strike-slip motion withsome reverse component. The mechanism of the 1987event indicates a strike-slip motion with a notablenormal component (Abu elenean 1993).

3. The Western Egyptian Mediterranean Coastal zone(WEM) experiences earthquake activity due to themovement of Africa towards Europe. The focalmechanism analyses available for most of the earth-quakes indicate reverse faulting with some strike-slipcomponent.

In addition to the 17 seismogenic zones mentionedabove, the 6 zones of intermediate depth in the AegeanSea (Papazachos 1990) and Cyprus are included in thisstudy. Earthquakes not included in the selected zonesare considered as background seismicity, thus a total of25 seismogenic zones have been considered in this study.

Earthquake selection and magnitude recurrenceparameters

Earthquakes with epicentres within each seismogeniczone were selected from the compiled catalogue:

Magnitude ‡ 3.0 since 1997,Magnitude ‡ 3.6 since 1962, andMagnitude ‡ 5.0 since 1897.

Historical earthquakes with a magnitude equal to orgreater than 5.5 were considered along the entire length ofthe catalogue (i.e. from 184 BC).Magnitude intervals of 0.1were used to display the recurrence curves although formany events the magnitude uncertainty is of a higher or-der. No explicit correction for the magnitude uncertaintyhas been attempted (Rhoades and Dowrick 2000).

As the data were assumed to be Poissonian, the earth-quakes were considered to be independent, hence depen-dent events (foreshocks and aftershocks) were removedfrom the catalogue using the clustering criteria of theZMAP program (Weimer and Zuniga 1999). To charac-terize the seismicity of the region, the Gutenberg andRichter model (Gutenberg and Richter 1954) was used.

314 M. El-Hefnawy et al.

logNðMÞ ¼ a � bM : ð1Þ

N is defined as the number of earthquakes of mag-nitude ‡ M per year and is found by summing thecumulative number of events from the largest magnitudedownwards and dividing this by the completeness timeperiod. The parameter ‘‘a’’ is the activity while the ‘‘b’’value defines the relative proportions of the small andlarge earthquakes. Determination of the parameters ofthe Gutenberg and Richter relation was undertakenusing a least-squares technique (see Table 1).

Maximum magnitude

In any region, there is an upper bound on the size ofearthquake that can be generated, limited by the extentof the largest seismogenic structure. The function of thisupper bound magnitude is to truncate the recurrencerelationship at the limit of the seismogenic potential ofthe source. The value of the maximum magnitude isestimated by identifying the length of the faults and thenusing empirical relationships to estimate the magnitude

Table 2 Location parameters and focal mechanism solution for earthquakes with magnitude greater than 4 and shown in Fig. 3

No. Date Time Location Magnitude Fault planes Stress axes References

Date Month Year Hour Minute Second Latitude Longitude NP1 NP2 P-axis T-axis

St. Dip St. Dip St. Dip St. Dip

1 30 01 1951 23 07 24.00 32.40 33.40 5.7 162 34 295 64 165 60 42 17 Costantinescu et al. (1966)2 12 09 1955 06 09 00.00 32.20 29.70 6.7 116 68 215 68 346 2 78 28 Costantines et al. (1966)3 02 01 1967 08 19 37.00 32.40 22.66 4.6 59 69 290 31 167 20 295 59 Abu Elenean (1993)4 31 03 1969 07 15 54.00 27.61 33.91 6.9 294 37 113 53 19 82 203 8 Huang and Solomon

(1987)5 28 04 1970 03 20 00.00 27.70 33.60 4.8 335 70 65 90 108 13 201 13 Salamon et al. (2003)6 08 07 1971 23 40 00.00 27.20 33.70 5.1 160 25 328 65 139 69 322 20 Salamon et al. (2003)7 12 01 1972 08 15 00.00 27.50 33.70 5.0 155 30 301 64 91 66 313 17 Salamon et al. (2003)8 28 06 1972 09 49 35.00 27.70 33.80 5.5 288 40 121 51 75 82 205 5 Huang and Solomon

(1987)9 29 04 1974 20 04 39.00 30.52 31.72 4.8 78 85 347 86 302 10 33 2 Hassib (1990)10 07 03 1978 22 33 46.60 34.48 25.24 5.4 297 73 53 64 252 36 337 6 Badawy (1990)11 13 06 1980 02 08 37.00 33.79 23.07 5.0 26 50 238 50 310 0 222 56 Abu Elenean (1993)12 17 08 1982 22 22 20.00 33.71 22.94 6.1 20 76 276 54 146 12 244 38 Abu Elenean (1993)13 30 10 1982 04 36 46.20 27.80 34.00 4.5 342 82 76 72 296 22 18 5 Mousa (1989)14 12 06 1983 12 00 09.00 28.50 33.20 5.3 129 86 219 83 ) ) ) ) Maamoun (1985)15 29 03 1984 21 36 06.00 30.18 32.10 4.7 27 75 164 70 120 4 28 21 Mousa (1989)16 22 07 1985 21 32 27.90 34.38 28.30 5.4 179 82 84 62 44 27 309 13 Badawy (1990)17 02 01 1987 10 14 46.00 30.46 32.22 5.0 156 80 158 80 112 14 22 0 Megahed and

Dessouky (1988)18 09 04 1987 03 00 04.00 32.39 28.97 4.6 186 56 290 70 152 41 56 6 Abu Elenean (1993)19 28 06 1987 00 50 17.00 32.82 24.35 5.2 109 59 264 33 52 64 192 12 Abu Elenean (1993)20 28 01 1988 15 48 00.00 32.41 21.15 4.8 26 74 253 24 139 25 286 61 Abu Elenean (1993)21 09 06 1988 02 18 24.00 32.23 27.90 4.7 83 71 300 26 187 24 338 61 Abu Elenean (1993)22 05 10 1991 18 48 26.00 29.52 32.58 4.3 283 50 153 53 125 62 219 2 Abu Elenean (1993)23 12 10 1992 13 09 57.50 29.77 31.07 5.8 166 58 282 57 134 52 225 4 Abu Elenean (1993)24 22 10 1992 17 38 57.8 29.60 31.10 4.0 138 29 278 67 159 64 22 20 Abu Elenean (1993)25 5 11 1992 18 41 50.50 29.68 31.10 4.2 161 66 254 83 120 22 25 12 Abu Elenean (1993)26 10 11 1992 11 17 18.80 29.60 31.10 4.0 163 49 263 78 132 37 27 19 Abu Elenean (1993)27 08 09 1995 12 13 22.00 29.49 32.25 4.2 123 65 256 34 72 62 195 16 Abu Elenean (1993)28 09 06 1997 15 21 02.00 27.53 34.19 4.8 265 75 149 32 142 52 16 25 Abu Elenean (1997)29 28 05 1998 18 33 28.00 31.40 27.66 6.0 313 57 86 43 22 8 276 64 Bulletin of ENSN (2000)30 05 06 1998 18 26 58.00 27.98 33.73 4.5 256 49 2 42 222 82 340 4 Abu Elenean (1997)31 11 10 1999 20 39 34.00 28.65 31.54 5.1 319 77 56 63 275 29 10 9 Bulletin of ENSN (2000)32 28 12 1999 12 05 11.00 30.29 31.45 4.3 302 45 79 54 290 66 189 5 Bulletin of ENSN (2000)33 25 06 2000 19 18 48.00 28.21 33.48 4.6 196 77 103 76 59 19 329 1 Bulletin of ENSN (2000)34 29 06 2000 14 44 49.00 29.53 31.60 4.0 286 35 109 55 27 79 198 10 Bulletin of ENSN (2000)35 03 11 2000 21 19 03.00 28.93 32.80 4.4 319 77 56 63 275 29 10 9 Bulletin of ENSN (2000)36 12 06 2001 12 43 26.30 29.62 31.12 4.1 104 50 309 43 311 77 25 4 Bulletin of ENSN (2001)37 20 08 2001 16 31 52.00 27.48 33.92 4.6 180 74 88 83 43 16 135 6 Bulletin of ENSN (2001)38 17 12 2001 04 25 33.50 29.57 30.88 4.2 321 43 125 48 329 81 223 3 Bulletin of ENSN (2001)39 24 08 2002 20 01 21.2 30.14 31.35 4.3 291 52 68 47 264 67 0 2

ENSN Egyptian National Seismological Network

Probabilistic assessment of earthquake 315

that would be associated with rupture along the entirelength of the segment considered. Deif (2001) defined thefollowing relation between the seismic moment and therupture length.

LogðMoÞ ¼ 2:8348 log ðLÞ þ 12:3836; ð2Þ

where Mo is the seismic moment in dyn.cm and L is therupture length in metres. The output of the above rela-tionship is converted into surface wave magnitude usingthe Deif (1998) relationship.

LogðMoÞ ¼ 1:44ð� 0:051ÞMsþ 16:375ð� 0:293Þ: ð3Þ

For seismogenic zones with unidentified faults, themaximum magnitude is estimated by adding an incre-ment to the largest known magnitude in the source fromthe instrumental or historical record. This increment isusually taken to be 0.5, although clearly this could bemisleading. Table 1 shows the estimated maximummagnitudes for the selected seismogenic zones.

Strong ground motion relation

Deif (1998) found an attenuation law for the EasternMediterranean region. The bulk of the data used wasobtained from the European strong motion records

published by Ambraseys and Bommer (1991). Their dataset contains the records of earthquakes in the regionextending from the Azores in the west to Pakistan in theeast. A subset of the data for the Eastern Mediterraneanregion was extracted from the whole data set. Deif(op.cit) transformed the velocity records of the reason-able earthquakes recorded by the Egyptian broadbandMIDNET station (KEG) into acceleration and addedthe results to the database. Adopting the model pro-posed by Joyner and Boore (1981), an attenuation of thepeak horizontal acceleration (ah), as well as the peakvertical acceleration (av) in terms of body and surfacewave magnitudes was introduced.

logðahÞ ¼ �1:86þ 0:385mb� logR ð4Þ

logðahÞ ¼ �1:26þ 0:273Ms� logR� 0:00023R ð5Þ

logðavÞ ¼ �2:257þ 0:407mb� logR� 0:00039R ð6Þ

logðavÞ ¼ �1:62þ 0:288Ms� logR� 0:00044R; ð7Þ

Fig. 5 Seismogenic zones of Egypt and its surrounding

Fig. 6 Peak ground acceleration with 90% probability of not beingexceeded in 50 years

316 M. El-Hefnawy et al.

where R is the hypocentral distance. The formula of thepeak horizontal acceleration in terms of surface wavemagnitude is used in the present study. The standarddeviation of the logarithm of the horizontal accelerationof this formula is 0.28.

The influence of site conditions has not been includedin the above analysis. For the European data set, siteshave been classified as either rock or alluvium dependingupon the surface geology and without regard to thenature of the deposits at depth. Horizontal accelerationin alluvial sites is considered to be less than 10% greaterthan in rock sites. The site geology is important in pre-dicting strong motion, but with the level of informationthat was generally available for the European stations,the classification that can be applied is insufficientlydetailed to reveal the influence.

Ground motion hazard map of Sinai

Seismic hazard values were calculated for a 0.25� gridextending over Sinai and its neighbouring regions. Thesevalues were used to create two peak ground acceleration

(PGA) contour maps with a 90% probability of notbeing exceeded in the next 50 and 100 years (Figs. 6, 7).The seismic hazard maps reveal that the region ofhighest hazard is the Gulf of Aqaba zone. The hazard isalso relatively high around the Dead Sea and at thesouthern part of the Gulf of Suez. The rest of Sinai ischaracterized by a relatively low hazard, as the values ofthe PGA with a 90% probability of not being exceededin 50 years do not exceed 100 gal; the high hazard areasare where a maximum acceleration of more than 200 galis expected with a 90% probability of not being exceededin 100 years.

The pattern of hazard is closely related to thegeometry of the seismic source zones adopted. As theperiod increases, the acceleration value at a particularplace proportionally increases, therefore the shape of theisoacceleration map does not significantly change.

Discussion and conclusion

The results of the present study have been comparedwith those of the Global Seismic Hazard AssessmentProgram (GSHAP). The GSHAP map is similar as re-gards the relatively high hazard values around the Gulfof Aqaba, Dead Sea and the Gulf of Suez, althoughnaturally the GSHAP source zone model is very gener-alized and lacks many of the specific zones in the presentstudy. The GSHAP map is calculated for a 90% prob-ability of not being exceeded in 50 years on rock. Itcompares well with the hazard values in this study,bearing in mind the uncertainty in reading values off themore generalised GSHAP map.

As the attenuation model used does not differentiatebetween soil and rock sites, a detailed study for specificsites is highly recommended. Effects including the loweramplification of strong motion with strong shaking, thede-amplification of short period motions in thick soils,and the change of spectral shape according to soil soft-ness should be considered.

Statistical variability in ground motion attenuationrelations is a significant source of uncertainty. Thestandard deviations in the log peak ground horizontalacceleration of Deif’s (1998) formula is 0.28 and isgenerally assumed to hold for all magnitudes and dis-tances. To illustrate the effect of this uncertainty on theestimated ground motion of this study, the variability inthe attenuation model was introduced into the SEIS-RISK III calculations. The results show that incorpo-rating attenuation variability increases ground motionby as much as 30% for the highest levels of the groundmotion; for low hazard regions the increases are con-siderably less.

Secondary ground failure hazards resulting fromearthquakes, such as surface rupture, liquefaction andlandsliding, have not been considered in the present

Fig. 7 Peak ground acceleration with 90% probability of not beingexceeded in 100 years

Probabilistic assessment of earthquake 317

study. However, a thorough understanding of earth-quake hazard would include a knowledge of those areassusceptible to induced ground failure. There is fieldevidence for liquefaction phenomena during the 1995Nuweibaa earthquake in Sinai.

The estimated PGA could contribute significantly tothe determination of the national seismic codes. Theseresults could be a tool for engineers, regulators andplanners to mitigate the earthquake effects and allowthem to plan earthquake resistant design.

References

Abdel-Rahman MA, El-Etr HA (1978) Theorientational characteristics of thestructure grain of the Eastern Desert ofEgypt, In: Symposim of evolution andmineralization of the Arabian-NubianShield, Inst Appl Geol Jeddah, SaudiArabia

Abdel-Rahman MA, El-Etr HA (1979)Structural pattern of the northern partof the Eastern Desert as viewed fromApollo-Soyuz photographs, In: Apollo-Soyuz Test Project Summary ScienceReport, NASA, SP-412, pp 87–96

Abou Elenean K (1993) Seismotectonics ofthe Mediterranean Sea North of Egyptand Lybia, MSc Thesis, Faculty ofScience, Mansoura University

Abou Elenean K (1997) A study on theseismotectonic of Egypt in relation tothe Mediterranean and Red Seas tec-tonics. PhD Thesis, Ain ShamsUniversity

Ambraseys NN, Bommer JJ (1991) Data-base of European strong motion re-cords. Eur Earthquake Eng 5(2):18–37

Ambraseys NN, Melville CP, Adams RD(1994) The seismicity of Egypt, Arabiaand the Red Sea, a historical review,King AbdulAziz City for Science andTechnology. Cambridge UniversityPress, Amsterdam, pp 1–137

Badawy A (1990) Seismotectonic study ofthe Eastern Mediterranean Region.MSc Thesis, Faculty of science,Mansoura University

Ben Avraham Z, Nur A, Cello G (1987)Active transcurrent fault system alongthe north African passive margin.Tectonophysics 41:260–294

Bender B, Perkins D (1987) SEISRISK III,a computer program for seismic hazardestimation. US Geol Surv Bull 1772:48

Ben Menahem A, Nur A, Vered M (1976)Tectonics, seismicity and structure ofthe Afro-Eurasian junction: the break-ing of an incoherent plate. Phys EarthPlanet Inter 12:1–50

Constantinescu L, Rubrechtova L, EnescuD (1966) Mediterranean-Alpine Earth-quake mechanisms and their seismo-tectonic implications. Geophys J RAstron Soc 10:347–368

Daggett P, Morgan P, Boulous F, HenninS, El-Sherif A, El-Sayed A, Basta N,Melek Y (1986) Seismicity and activetectonics of the Egyptian Red Seamargin and the northern Red Sea.Tectonophysics 125:313–324

Deif A (1998) Seismic hazard assessment inand around Egypt in relation to platetectonics. PhD Thesis, Ain ShamsUniversity

Deif A, Tealeb A (2001) Deterministicseismic hazard assessment for Toshkaand High Dam projects. Bull Natl ResInst Astron Geophy (B), pp 233–263

Dubertret L (1955) Carte geologiqe duLiban, scale 1: 500000, Naqure, BentJabil, Tyr-Nabatiya and Marjayoung,Beyrouth

Egyptian Geological Survey and MiningAuthority (1981) Geological map ofEgypt

El-Hadidy S (2000) Egyptian NationalSeismological Network bulletin ENSN.NRIAG J Geophys 4(1):1–21

El-Hadidy S (2001) Egyptian NationalSeismological Network bulletin ENSN.Acta Geophys 11(1)

Eyal M, Eyal Y, Bartov Y, Steinitz G(1983) The tectonic development of thewestern margin of the Gulf of Aqabarift. Tectonophysics 80:39–66

Gardosh M, Reches Z, Grfunkel Z (1990)Holocene tectonic deformation alongthe western margins of the Dead SeaRift. Phil Trans R Soc Lond A 267:107–130

Garfunkel Z, Bartov Y (1977) The tectonicof the Suez Rift. Israel Geol Surv Bull71:44

Garfunkel Z, Zak I, Freund R (1981) Ac-tive faulting in the Dead Sea rift. Tec-tonophysics 80:1–26

Gerson R, Grossman S, Amit R, Green-baum N (1993) Indicators of faultingevents and periods of quiescence indesert alluvial fans. Earth Surf Pro-cesses Landforms 18:181–202

Giardini D (1999) The Global SeismicHazard Assessment Program(GSHAP)—1992/1999. Annali di geofi-sica 42:957–976

Gutenberg B, Richter CF (1954) Seismicityof the earth and associated phenomena.Princeton University Press, Princeton

Hassib GH (1990) A study of focal mech-anism for recent in Egypt and theirtectonic implication, MSc Thesis, Fac-ulty of Science, Assiut University

Hofstetter a van Eck T, Shapira A (1996)Seismic activity along fault branch ofthe Dead Sea–Jordan Transform sys-tem: the Carmel-Tirtzsa fault system.Tectonophysics 267:317–330

Huang PY, Solomon SC (1987) In: Geo-thermal evolution of the Red Sea mar-gin and its relation to earthquakeactivity (El-Hady SM, 1995). MSc,Cairo University

Jackson JA, McKenzei DP (1984) Activetectonics of the Alpine Himalayan Beltbetween Western Turkey and Pakistan.Geophys J R Astro Soc 77:185–264

Joyner WB, Boore DM (1981) Peak hori-zontal acceleration and velocity fromstrong motion records including recordsfrom 1979 Imperial Valley, California.Bull Seism Soc Am 71:2011–2038

Klinger Y, Avouac J, Dorbath L, AbouKaraki N, Tisnerat N (2000) Seismicbehaviour of the Dead Sea fault alongAraba Valley, Jordan. Geophys J Int142:769–782

Maamoun M (1985) Shukeir earthquakeJune, 12th, 1983, Gulf of Suez, Egypt:Radiation pattern of first motion and itstectonic implication, HIAG Bull, 5,Ser B

Maamoun M, Ibrahim E (1978) Tectonicactivity in Egypt as indicated by earth-quakes. Bull HIAG No. 170

Maamoun M, Megahed A, Allam A (1984)Seismicity of Egypt. Bull HIAG 4(SerB):109–162

Megahed A, Dessouky M (1988) TheIsmailia (Egypt) earthquake of January2nd, 1987 (Location, Macroseismicsurvey, Radiation pattern of first mo-tion and its tectonic implications). In:1st Conference on environmental stud-ies and research, Cairo-Egypt

Meshref W (1990) Tectonic framework. In:Said R (ed) The geology of Egypt. A. A.Balkema, Rotterdam, pp 113–155

Mousa HH (1989) Earthquake activity inEgypt and adjacent regions and itsrelation to the geotectonic features.MSc Thesis, Faculty of Science,Mansoura University

318 M. El-Hefnawy et al.

Papadopoulos GA (1987) Seismicity andrelated phenomenon in the HellenicArc, Third symposium on the geologyof Libya, Tripoli, pp 27–30

Papazachos BC (1990) Seismicity of theAegean and surrounding area. Tec-tonophysics 178:287–308

Papazachos B, Papazachos C (1997) OnGreek earthquakes. Ziti publications,Thessaloniki, pp 1–340

Poirier JP, Taher MA (1980) Historicalseismicity in the Near and Middle East,North Africa, and Spain from Arabicdocuments (VIIth–XVIIth century).Bull Seism Soc Am 70:2185–2201

Rhoades d, Dowrick D (2000) Effect ofmagnitude uncertainties on seismichazard estimation. In: Proceedings ofthe 12th world conference on earth-quake engineering, Auckland, NewZealand Paper 1179 on CD-Rom,pp 1–8

Ron H (1984) Paleomagnetic investigationof the fault structure of Galille-North-ern Israel (In Hebrew with English ab-stract). PhD Thesis, Hebrew University,102 pp

Rotstein Y, Burner I, Hofstetter A (1993)High resolution seismic imaging of theCarmel fault and its implications to thestructure on MT. Carmel Isr J Earth Sci42:55–69

Salamon A, Hofstetter A, Garfunkel Z,Ron H (2003) Seismotectonics of theSinai subplate—the eastern Mediterra-nean region. Geophys J Int 155:149–173

Shamir G, Bartov A, Fleischer L, Arad V,Rosensaft M (2001) Preleminary seismiczonation, Geological survey of IsraelReport No GSI/12/2001, GeophysicalInstitute of Israel Report No GII 550/95/01/ (1), pp 9

Thenhaus P, Algermissen ST, Perkins D,Stanley LH, Williams HD (1993)Probabilistic estimates of the seismicground motion hazard in western SaudiArabia, in earthquake risk reduction inthe Eastern Mediterranean region,Cairo, Egypt

Weimer, Zuniga (1999) Zmap program,from the Internet

Probabilistic assessment of earthquake 319