IC/99/34

United Nations Educational Scientific and Cultural Organizationand

International Atomic Energy Agency

THE ABDUS SALAM INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS

DETERMINISTIC SEISMIC HAZARD IN EGYPT

A. El-SayedDepartment of Earth Sciences, Trieste University, Trieste, Italy,Geological Department, Mansoura University, Mansoura, Egypt

andThe Abdus Salam International Centre for Theoretical Physics, SAND Group,

Trieste, Italy,

F. VaccariDepartment of Earth Sciences, Trieste University, Trieste, Italy

andCNR-GNDT, Gruppo Nazionale per la Difesa dai Terremoti, Rome, Italy

and

G.F. PanzaDepartment of Earth Sciences, Trieste University, Trieste, Italy,

CNR-GNDT, Gruppo Nazionale per la Difesa dai Terremoti, Rome, Italyand

The Abdus Salam International Centre for Theoretical Physics, SAND Group,Trieste, Italy.

MIRAMARE - TRIESTE

April 1999

Abstract

The regional seismic hazard in Egypt is assessed using a deterministic approach, based

on the computation of synthetic seismograms at a set of grid points located at distances of 0.2°

from each other. The main input for this computation are earthquake sources and structural

models. The earthquake sources are parametrized using focal mechanism, seismogenic areas

and regional seismicity. A number of deep seismic profiles have been used to define the crustal

structures. Similar sets of gravity profiles have been used to define the density of the layers.

The peak displacement (DMAX), peak velocity (VMAX) and design ground acceleration

(DGA) are chosen and plotted to construct the seismic hazard maps. There are similarities

between computed and observed amplitudes of ground motion in terms of their values and

spatial distribution. The results obtained from the deterministic and probabilistic approaches are

comparable. The areas of high seismic hazard level are of great socio-economic importance.

1- Introduction

In Egypt, the population, archaeological sites and sensitive structures are concentrated

within a narrow zone around the Nile valley that occupies onlyl% of the total area of

the country. Nevertheless, both the population and the newly developed areas in this

zone are still growing rapidly.

In general, buildings in Egypt are not designed to resist earthquakes, therefore,

relatively small events can be the source of huge socio-economic disasters. The event

of October 12,1992 is an example of a small but damaging earthquake in Egypt. This

event has magnitude (mb) = 5.4, but still, 554 persons have been killed, about 20,000

people injured and over one billion US$ had been reported as property losses. This is

not the only destructive earthquake in Egypt, but similar events occurred in 778, 1303

and 1847. These earthquakes destroyed parts of big cities, like Cairo and Alexandria

(Ambraseys et al., 1994; El-Sayed, 1996).

The economic and social effects of earthquake disasters can be reduced through a

comprehensive assessment of seismic hazard and ri^k for areas like Egypt. Such a

study leads to increase public awareness, consequently upgrading the existing

buildings and engineering works as well as reliable earthquake resistant design for

new structures. Loss of life and property damage can be substantially reduced by

highly detailed, specific prediction of seismic ground motion and related damage

scenarios. With the knowledge of the geological structure and probable earthquake

source mechanisms, realistic ground motion at all sites of interest can be determined.

Instead of waiting for the earthquakes to occur and to record the ground motion in

Egypt using a dense network, we can map the ground motion by computing complete

synthetic strong motion records and testing their reliability against the available

information (e.g. Panzaet al., 1999a,b).

An attempt to estimate seismic hazard in Egypt using Poisson probabilistic seismicity

model has been done by El-Sayed (1996) after the destructive earthquake of October

12, 1992. The obtained results indicate that the level of seismic hazard is relatively

high in densely populated areas that can affect the socio-economic development of the

country.

The main aims of the present study are (1) to map the possible seismic ground motion

using a deterministic approach, (2) to create a synthetic seismogram database for the

studied area for further investigation, and (3) to compare the results obtained with the

deterministic and the probabilistic approaches.

2- Method

A deterministic approach to estimate the seismic hazard has been developed by Costa

et al. (1992 and 1993) and subsequently applied to several regions of the world (e.g.

Orozov-Stanishkova et al., 1996; Radulian et al., 1999; Alvarez et al., 1999; Aoudia et

al., 1999; Panza et al., 1999a). The procedure uses the available information on the

earth structure parameters, the seismic sources and the level of seismicity of the area

to compute synthetic seismograms. Once calibrated against the available information,

the synthetic seismograms allow us to estimate in a rather realistic way the

engineering parameters needed to assess the seismic hazard, even in those areas where

scarce (or none) historical or instrumental information is available. Moreover, the

method allows us to evaluate the influence of different input parameters on the final

result. The immediate outcome of the procedure are maps showing the distributions of

the peak displacement (DMAX), peak velocity (AMAX) and design ground

acceleration (DGA), over the investigated territory. The details of the technique are

given by Costa et al. (1993) and Panza et al. (1999a). As shown by Aoudia et al.

(1999), the method can directly include information on maximum possible magnitude

based on geological studies.

The deterministic approach followed in the present paper is completely different and

complementary to the probabilistic one as in general proposed. It highlights some

issues largely overlooked in the probabilistic approach: (a) the effect of crustal

properties on attenuation are not neglected, (b) the ground motion parameters are

derived from synthetic time histories and not from over simplified attenuation

"functions"; (c) the resulting maps are in terms of design parameters directly, and do

not require the adoption of probabilistic maps to design ground motion, (d) such maps

address the issue of the deterministic definition of ground motion in a way which

permits generalization to locations where there is little seismic history.

3- Input

The input data needed to compute synthetic seismograms consist of four main

sections: earthquakes catalogue, seismogenic zones, focal mechanisms, and structural

models.

The earthquakes catalogue used in this study has been assembled for the area located

between latitude 20°-35<>N and longitude 22°-38°E for the time period 184 bC-1998.

The temporal distribution of the reported events shows that our catalogue contains

three periods of observations that are represented by the historical (184 bC-1899),

early instrumental (1900-1960) and recent instrumental period (1961-1998).

Ambrasyes et al. (1994) revised the existing historical catalogues for Egypt and

produced a catalogue of historical earthquakes with location and Mf magnitude

(equivalent to Ms) given for most of the events. We use this catalogue for the period

(184 b C - 1899).

For both early and recent instrumental periods, the information has been assembled

from computer files stored at WDC.A, published catalogues, CD products of the ISC

and NEIC (Table 1). The duplicate events were removed after reviewing the various

sources, giving the preference to the sources that included more complete and recent

information.

Different agencies report different magnitudes, i.e., some agencies report ML, others

Ms, m,, Mw, ML or MD (see Table 2). The difference between these values can be as

large as one magnitude unit. Moreover, the same kind of magnitude reported by

different agencies for the same event may differ by 0.5. Consequently, the acritical

compilation of data from different catalogues could be a source of large errors. To

minimize these errors all the compiled data should be homogenized to the same

magnitude. In our case, we have used the duplicates, i.e., the magnitude reported for

the same event by different agencies, to construct linear relations between the

different magnitudes (Table 2). In our compilation, for each earthquake, we give three

magnitudes (mb, Ms and ML), either reported or obtained from other magnitudes. The

largest of them is considered for the calculation of the synthetic seismograms. The

distribution of the collected earthquake epicenters is shown in Figure 1.

Tectonic evidence suggests that the earthquakes in the area are shallow events

concentrated in the crust; and there is nothing in the macroseismic data to indicate the

contrary (Ambraseys et al., 1994). The recent part of the instrumental observation

supports the tectonic evidences and only in areas close to Crete and Cyprus few

earthquakes at intermediate depths are recorded.

The completeness of the catalogue for the two periods of instrumental observation has

been analyzed. The early part of the catalogue is complete up to the events of

magnitude 5.0 and larger, while after 1960's it seems to be complete for the events of

magnitude 3.5 and larger. However, this difference in completeness does not affect

our calculations since in the deterministic procedure we use events of magnitude 5.0

and larger.

The seismogenic zones represent areas that are characterized by a specific level of

seismicity, stress regime and tectonic behavior, which is assumed to be homogeneous

within the zone. A large amount of geologic, tectonic and seismological information

has been analyzed to define these zones.

The primary features of active plate tectonics in the vicinity of Egypt are discussed in

detail by many authors: McKenzie (1970), McKenzie et al. (1970), Neev (1975), Riad

(1977), Ben-Avraham (1978), Ben-Menahem et al. (1976), Garfunkel and Bartov

(1977), Sestini (1984) and Mesherf (1990). There are three major plate boundaries

located near Egypt: the African-Eurasian plate margin, the Levant transform fault, and

the Red Sea plate margin. They separate the African, Eurasian and Arabian plates. A

piece of the African plate, called the Sinai block or subplate, is partially separated

from the African plate by the spread-apart or rifting along the Gulf of Suez

(Woodward-Clyde Consultants, 1985). In addition to these plate boundaries, there is a

megashear zone running from southern Turkey to Egypt (Neev, 1975; Kebeasy, 1990)

marked by relatively moderate and scattered seismicity (Fig. 2). The interaction

between the mentioned plate boundaries has created active areas in/and around Egypt.

In general, four major seismogenk zones can be identified in Egypt, namely: (1) Gulf

of Aqaba-Levant zone, (2) Northern Red Sea-Gulf of Suez, (3) Suez-Cairo-

Alexandria fault zone and (4) Eastern Mediterranean-Cairo-Fayoum zone (Kebeasy,

1990; Maamoun and Ibrahim, 1978; Reborto et al., 1992; Mohammed, 1993; El-

Sayed and Wahlstrom, 1996). In addition to these zones, Kebeasy (1990) defined

other local seismic zones, e.g., Gilf El-Keber, Aswan and Qena local source zones (8,

9 and 10 in Fig. 2). Since distant earthquakes have caused considerable damage in

Egypt, three remote seismogenic zones, i. e., Egypt-Mediterranean-Coast, Cyprus and

Crete (5, 6 and 7 in Fig. 2) have been included in this study. Figure 2 shows the major

seismogenic zones used in the present study.

The focal mechanisms database that may describe the geodynamic characteristics of

the seismogenic zones in Egypt is based on the Centroid Moment Tensor (CMT)

catalogue. In total, there are 41 CMT focal mechanism solutions available for the

studied area. CMT solutions are reported only for events with magnitude > 5.0. The

distribution of the earthquake epicenters shows that, in some active areas, the energy

is released through small earthquakes, i.e., M < 5.0, consequently, such areas do not

have any focal mechanism solution in the CMT database. There is a relevant number

of focal mechanism solutions available for earthquakes with magnitude 4.0 - 5.0

(Abo-Elenean, 1993), from which only the events that have a well-constrained focal

mechanism were selected. The focal mechanism database that we have assembled

contains 57 events (Fig. 3 and Table 3).

Egypt is characterized by complicated tectonics. Hence, focal mechanism solutions of

events that occur within the same seismogenic zone are different (Fig 3). With our

approach, it is preferable to choose one representative focal mechanism for each

seismogenic zone (Fig 3, Table 3). The selection of the representative events is based

on the known tectonics of the area as well as on the size of the earthquake. For

example, there are 10 focal mechanisms available for the Gulf of Aqaba-Levant

seismogenic zone, and the focal mechanisms of these events are considerably

different; based on the known tectonics, the mechanism of the largest event of the

November 22, 1995 (Ms=7.3) is chosen as representative for the whole zone.

The regional polygons are the surface boundaries of different structural models that

characterize the lithospheric properties of the studied area. These structural models

are represented by a number of flat layers. The thickness, density, P- and S-wave

phase velocity and quality factor are given for each of these layers.

In the present study, the Egyptian territory is subdivided into five regional polygons

(Fig. 4), that take into account the available tectonic, geological and geophysical

characteristics described by Mesherf (1990) and Said (1990). The thickness of the

earth's crust, the density and the P-wave and S-wave velocity models are taken from

deep seismic sounding and Bouguer anomaly profiles published by the Egyptian

General Petroleum Company (GPC). These data are stored in the Atlas of Geology at

Cornell University, USA (Barazangi et al., 1996). The S-wave velocity is assigned to

be Vp/1.73. The quality factors are taken from Xie and Mitchell (1990). For the

uppermost part of the crust there is a large number of geological wells that are drilled

as deep as 3.5 km (Said, 1981), as well as shallow seismic profiles (El-Gamili, 1982;

Marzouk, 1995 and Mohammed, 1995) that give the details of the upper 300 meters.

These detailed profiles are concentrated in the Nile Delta and Nile valley area. Due to

the lack of specific models, for the upper mantle we have considered a standard

continental model (Harkrider, 1970; Du et al., 1998).

4- Calculations

The calculation of the set of seismograms is made as follows, starting from the basic

knowledge of the seismicity and of the structural models.

4.1- Definition of seismic sources and observation points

The seismic sources used in the computation of the synthetic seismograms are defined

in two steps: (1) discretization of the observed seismicity and (2) smoothing of the

discretized seismicity within the seismogenic zones.

For the discretization of the seismicity the studied area is subdivided into cells (0.2°

by 0.2°). The magnitude of the strongest earthquake occurred within a cell is assigned

to the cell.

The smoothing procedure is applied to account, though in a rough way, for the source

dimension of the largest earthquakes, and for the location errors that may be

particularly severe for historical events (Costa et al., 1993; Panza et al., 1999a). The

seismogenic zctnes are introduced into the procedure as natural boundaries in the

smoothing process. After the smoothing of seismicity, only the sources falling within

the seismogenic zones are taken into account for the computations of synthetic

seismograms.

Each seismic source is represented by one double couple located in the center of each

cell. This source replaces all the events falling within the cell and its strength is

determined according to the maximum magnitude in the cell after smoothing. The

orientation of the double-couple source is determined on the basis of the available

fault plane solutions.

The observation points are placed at a grid with dimension of 0.2° by 0.2° over the

whole studied area. They do not overlap with the sources, because the sources are

placed in the center of each cell falling within the seismogenic zones, whereas, the

observation points are placed at the corners of the grid.

4.2- Ground motion parameters

When the seismicity, the source mechanisms, the structural models and the

observation points are defined, synthetic signals are computed using the modal

summation technique (Panza, 1985; Panza and Suhadolc, 1987; Florsch et al., 1991).

To study the ground motion in Egypt, around 2500 seismic sources are used. The

horizontal P-SV (radial) and SH (transverse) components of motion are computed andi

rotated to the common reference system (NS and EW direction), then their vector sum

is calculated. The total number of seismograms expected for the above configuration

would exceed 32 million. To reduce the computations, the source-receiver distance is

kept below an upper threshold (90 km at most), which depends on magnitude (Costa

et al., 1992; 1993; Panza et al., 1999a). At each observation point all seismograms

generated by different sources are examined and the largest component of ground

motion is selected for further analysis.

The synthetic signals are computed to obtain the peak ground displacement (DMAX),

velocity (VMAX) and acceleration (AMAX) up to a maximum frequency of 1 Hz.

The design ground acceleration (DGA) is obtained through extrapolation using

standard code response spectra. Since there is no building code available for Egypt,

the EC8 for the soil A (European code) is used in this study. The choice of the soil A

is justified by the fact that in all structural models the topmost S-wave velocity is

greater than 0.8 km/sec.

Since we compute complete time series it is possible to consider other parameters,

like Arias (1970) intensity or other'integral quantities (e.g., Uang and Bertero, 1990;

Decanini and Mollaioli, 1998) which are of great interest in seismic engineering.

To estimate the effects of distant earthquakes in Egypt, calculations have been carried

out taking into account only the large events reported in the Gulf of Aqaba, Cyprus

and Crete, and allowing source-receiver distances in the range of 100-1000 km (e.g.

see Fig. 6).

5- Results and Discussion

5.1- Effect of local earthquakes

The spatial distribution of DMAX, VMAX and DGA (Fig. 5), due to sources located

at most at an epicentral distance of 90 km, shows that the highest accelerations are

concentrated in the Nile Delta, Northern Red Sea and its two extensions (Gulf of

Suez-Gulf of Aqaba), and Aswan. For these areas the peak ground acceleration varies

from 0.005g to 0.34g. The results obtained from the probabilistic approach (El-Sayed,

1996) varying from 0.005g to 0.4g are in agreement with the result of the

deterministic approach. Based on the conversion table given by Panza e al. (1999a),

these values correspond to intensities in the range V-XL

In the Nile Delta DGA can be as high as 0.15g, corresponding to intensity in the range

VIH-IX (Panza et al., 1999a), and agrees with the value, 0.2g, obtained by El-Sayed

(1996) using the probabilistic approach. Intensity IX (MSK) has been reported for the

area in 1847 (Sieberg, 1932; Maamoun et al., 1984; Ambraseys et al., 1994). In 1992

an earthquake occurred to the south of the Nile Delta, with epicenter and magnitude

(Table 2) similar to those assigned to the 1847 event (Sieberg, 1932; Maamoun et al.,

1984), nevertheless, the observed intensities for the two events are K (1847) and VI

(1992) (Sieberg, 1932; Maamoun et al., 1984; Helwan Institute of Astronomy and

Geophysics, 1993; Ambraseys et al., 1994). The latter observed intensity value is in

very good agreement with the intensity (VI), calculated using the conversion table

given by Panza et al. (1999a). The large difference between the 1847 and 1992

intensities may be due to: (1) the large uncertainties associated with historical

parameters, i.e., the event of 1847 may have a larger magnitude or can be located

closer to the Nile Delta, (2) the focal depths may be different. For example, if we

assume that the event of 1847 has a magnitude 6.4 (instead of 5.9) and a focal depth

of 8 km (instead of 22 km), the calculated intensity, using the conversion table given

by Panza et al. (1999a), is VIII, a value quite close the reported one. In 1992 the event

has been moderate (mb = 5.4), but caused considerable damage, therefore larger

events in this area could be the source of a huge social disaster.

In the areas of high economic importance (the largest Egyptian oil fields) of the Gulf

of Suez, DGA can be as high as 0.25g (intensity around X). The results obtained by

using the probabilistic method (El-Sayed, 1996) indicate that the maximum expected

intensity and acceleration are X and 0.35g, in satisfactory agreement with the results

of this study. In 1969, an earthquake with magnitude 6.9 occurred in this area,

generating a great quantity of surface lineaments and dislocations implying a MSK

10

intensity of IX-X (Maamoun et al., 1984). At the time of the earthquake, the area was

not populated and there were only few oil wells, located far from the epicenter.

Presently, the area is relatively highly populated and there is a large number of drilled

wells along the Gulf of Suez. Therefore, such intensity could be a source of major

danger today.

In the region of the Aswan High Dam, DGA can be as high as 0.14g (intensity around

VEH). This result agrees well with the value of the probabilistic approach (0.15 g)

given by El-Sayed (1996). For this area the largest reported earthquake has m < 6.

The most recent earthquake is that of November 14, 1981 (mb=5.1). This earthquake

caused considerable damage in Aswan, but obviously did not affect the stability of

the High Dam. '

5.2- Effect of distant earthquakes

Distant earthquakes of magnitude 7.3 and larger can generate in the northern part of

Egypt intensity up to VIE. Such intensity is a source of danger for the poorly

constructed buildings, which are common in the high-populated area of the Nile Delta

(Fig. 6). This is confirmed by both recent and historical observations.

In fact more than half of the earthquakes that affect the Nile Valley and the Delta

originate from epicenters outside Egypt. These are generally large-magnitude

earthquakes in the Hellenic arc or in the Dead Sea system. Recent examples are the

events of March 31, 1969 (Northern Red Sea), November 22, 1995 (Gulf of Aqaba

Ms = 7.3) and October 9, 1996 (southern Cyprus Ms = 7.0). These earthquakes are

felt throughout the Nile Valley with isolated damage at epicentral distances greater

than 300 km (Ambraseys et al., 1994; El-Sayed 1996).

This phenomenon is due to the presence of thick unconsolidated, water saturated

sediments in the Nile graben (El-Sayed, 1996) that, in the case of distant earthquakes,

may allow the generation and propagation of local surface waves (Faeh et al., 1994)

that will affect mainly the taller buildings. Detailed site effect studies are needed to

quantify ground motion amplification in the Nile graben. The existing seismic

11

profiles, geological wells, gravity and magnetic data as well as the seismograms that

will be recorded with the seismic stations recently installed by the Helwan Institute of

Astronomy and Geophysics will help to further carry on this work.

5.3- Comparison between observed and model data

The event of November 22, 1995, which is located in the Gulf of Aqaba, can be used

to compare the observed and the calculated DGA values. This earthquake (Ms =7.3)

has triggered strong motion accelerographs belonging to the Jordanian and Israeli

network at Aqaba and Eliat cities, respectively. A preliminary analysis of the strong

motion records indicates that at the port city of Eliat (a distance of about 90 km from

the epicenter), the peak ground accelerations for the EW, NS and vertical components

are 0.09g, 0.08g and O.llg, respectively. From the Jordanian network, two recorded

values for the horizontal peak ground acceleration at two stations at epicentral

distance of about 96 km1 (one on sandy soil, the other on the rocky soil in Aqaba) is

O.lOg and 0.05g, respectively. There are no recording stations near to the epicenter. In

the city of Nuweiba, located 40 km North of the epicenter, the surveyed damage

suggests that the horizontal peak ground acceleration's in the range 0.16g-0.25g and

the vertical peak ground acceleration is in the range 0.16g-0.20g (Osman, 1996).

These observed values are comparable with the values we calculated for this

earthquake (considering distance and azimuth); in fact we got maximum values of

0.16g and 0.07g and 0.06g at distances of 43 km, 93 km and 96 km, respectively. The

points of the real and calculated

The earthquakes of 1955 (Alexandria offshore), 1969 (Gulf of Suez), 1982 (Aswan)

and 1992 (Cairo) are associated with maximum MSK intensities VIII, IX, VII and VI,

respectively (Maamoun et al, 1984). For these events the ground accelerations

calculated and converted into the corresponding intensity ranges, using the relation

given by Panza et al. (1999a), give VII-VIE, IX-X, V-VI and V-VI, respectively.

In general, the local match between synthetic computations and the few observations

available for the Gulf of Aqaba earthquake encourages the extension of the reliability

of our calculations to the rest of the area, where no surveys or observations are

12

available. Recently, a digital seismic network has been installed in Egypt by the

Helwan Institute of Astronomy and Geophysics and it is presently under testing. As

new data will be available they will be easily incorporated in our hazard maps.

6- Conclusion

The results obtained with the probabilistic and the deterministic approach are in

general very similar. The considerable differences in some areas may be related to the

following factors: the probabilistic methods (1) are very sensitive to the completeness

of the catalogue and (2) are using simple attenuation laws that oversimplify the wave

propagation phenomena.1

Earthquakes that are located within the Egyptian territory can generate ground

acceleration up to 0.15g, 0.25g and 0.35g (VIH-IX, IX-X and X-XI, MSK) in the

highly populated area of the Nile Delta, in the Gulf of Suez and in the Gulf of Aqaba,

respectively. These values are extremely high for the existing built environment and

could cause severe damage and huge socio-economic losses due to the high economic

importance of the areas.

Distant earthquakes, located as far as the Gulf of Aqaba, Cyprus and Crete (300-

800km) can generate ground acceleration up to 0.08g (VIII) in northern Egypt. The

energy in this case is carried by long period surface waves that could be mainly a

source of danger for tall buildings, long bridges and lifelines.

7- Acknowledgements

This work was carried on at the Department of Earth Sciences, Trieste University

(DST-UTS), Italy. Financial support was provided by ICTP, Italy. The first author is

highly indebted to Professors G. Furlan, Head of TRIL program ICTP and Refat EI-

Sherif, Head Geology Department, Mansoura University, for providing an excellent

opportunity to to visit DST-UTS and to produce commendable results for Egypt.

Thanks also to Drs. Marrara, Costa, Aoudia, Vecchies, Peresan, Sarao and all

members of the seismology group of DST-UTS who provided moral support and

rendered their services as and when required. Our thanks also to Professor Ota

Kulhanek, Uppsala University, Sweden, for his encouragement to start this work,

13

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Mesherf, W. M.: 1990, Tectonic. In R. Said (Editor), The Geology of Egypt. A.A.Balkema, Rotterdam, The Netherlands, 113-155.

McKenzie, D.: 1970, Plate tectonics of the Mediterranean region. Nature, 326: 239-243.

15

McKenzie, D., Davies, D. & Molnar, P.: 1970, Plate tectonics of the Red Sea and eastAfrica. Nature, 226: 243-248.

Mohammed, A. :1993, Seismic Microzoning study and its applications in Egypt.Ph.D. Theses, Ain Shams Univ., Egypt.

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17

Table 1. Catalogues used as sources in this study.

Source Catalogue

Ambraseys et al. (1994)

Poirier and Taher (1980)

European-Mediterranean Seismological Center

Gutenberg and Richter (Seismicity of the Earth)

International Seismological Bulletin data base

The Seismological bulletin of Israel

Preliminary Determination of Epicenters

International Seismological Summaries

Seismicity of Egypt (Maamoun et al., 1984)

Earthquake data file of the Mediterranean and

surrounding area

Covered

period

742-1981

528-1160

1902-1985

1904-1952

1964-1996

1907-1993

1869-1995

1913-1963

1900-1984

1901-1975

Number of

events

250

21

228

24

9893

4031

1611

110

216

236

18

Table 2. Relationships between magnitude determined by different agencies. IPRG =

seismological bulletin of Israel, ISC = International Seismological Center, PDE =

Preliminary Determination Epicenters, ATH = Athens, HLW = Helwan, EMSC =

European Mediterranean Seismological Center, MED = Mediterranean, mb = body

wave magnitude, ML = local magnitude, MD = duration magnitude and Ms =surface

wave magnitude.

Equation

ML(n>RG) = (1-02 0.29) + (0.74 0.07) ir^ ( i S Q

mb(PDE) = (0.43 0.08) + (0.91 0.02) ir^ (ISC)

ML(ATH) = (1-12 0.35) + (0.72 O.O^m^isC)

MD(HLW) = (1-97 0.27) + (0.55 0.07) mb (ISC) :

nyEMSC) = (0-73 0.20) + (0.73 0.05) mb (ISC)

Ms(EMSC) = (l-83 0.28)+ (0.60 0.06)mb(iSC)

ML(EMSC) = (0.96 0.20) + (0.98 0.04) mb (ISC)

MS(MED) = (0.89 0.20) + (0.79 0.04) mb (ISC)

ML(HLW) = (0.08 0.10)+ (1.01 0.02)mb(iSQ

Number of event used

127

460

34

23

125

51

29

139

Maamounet al., 1984

L9

Table 3. Events shown in Fig 6 and their focal mechanism parameters. Columns (1)Event number, (2) date, (3) origin time, (4) latitude (°N), (5) longitude (°E), (6) depth(km), (7) body wave magnitude, (8) strike, (9) dip, (10) slip in degrees and (11)bibliographical source of the solution: CMT, ABU and HU denote the HarvardCentroid Moment Tensor catalogue, Abo- Elenean (1993) and Huang and Solomon(1987), respectively.

11234567891011121314151617181920212223242526272829303132333435363738

1955 09 121969 03 311972 06 281974 04 291977 09 111978 03 071978 12 091979 04 231979 05 151979 06 151981 09 131981 11041982 09 171983 01 031983 03 191984 03 201984 07 021984 08 241984 08 241985 07 221985 09 271986 05 221986 10 021987 01 021987 04 091987 06 281988 06 051988 09 051989 03 171989 03 281989 06 141989 08 271990 07 091991 03 191991 10 051992 10 121992 10 201992 10 27

306 09 2407 15 5409 49 3520 04 3923 19 2722 33 4907 12 5613 015506 59 221134 1423 25 2509 05 3422 22 2900 12 2421 41 4921 36 060147 0906 02 2506 29 042132 3516 39 4819 52 2110 12 4610 144603 00 0400 50 2018 26 5820 03 3605 42 5313 29 1418 06 400121 171122 1412 09 2718 48 2613 09 5901 57 5809 44 46

432.2027.6127.7030.5234.5134.1924.000.5434.3834.8234.5623.8833.7033.9734.7530.1825.8632.8832.3834.1634.0534.1234.6530.4632.3932.5527.9834.5134.5134.0634.3034.2534.4534.6029.5229.7428.5128.84

529.6033.9133.8031.7222.9925.4526.4035.5924.8024.4225.1332.3822.9023.8924.8932.1033.8534.9134.8128.4026.9426.7229.1632.2228.9724.4933.7326.6525.5324.6826.1026.2826.2426.1332.5830.6333.1633.11

633.06.06.033.036.842.06.515.015.033.015.015.023.4102.065.010.010.039.028.015.043.833.215.020.010.015.017.015.017.055.915.015.033.015.031.022.010.010.0

76.16.15.94.85.85.45.35.15.65.64.85.16.05.45.64.75.15.15.05.45.55.15.35.04.65.24.54.94.85.45.15.05.15.44.35.93.83.4

8 9 10 1134 36 10 ABU294 37 -18 HU288 40 -103 HU78 8574225241

-176 ABU28 10014 40

197 40 -4172 4 -20216 11 10256 65 -11146 72 -15

34 9336 7039

134 56 048 -34

1324

67135 76227 37

37 -53-13

99136 80186 36 -30326 40 -7256 49 -80

5510

223 19 33

CMTCMT

58 150 ABUCMTCMTCMTCMTCMTCMTCMTCMTABU

21930358 39 13127 75 154281 45 -110 CMT54 51 151 ABU

CMTCMTCMTCMTCMTABUABUCMTABUCMT15 55 -11

77 10 -118 CMT67 53 29 CMT102 8 -68 CMT

CMT129 27 -106 CMT245 36 -33 CMT283 50 -132 ABU136 42 -75 CMT275261

6348

122 ABU-170 ABU

20

39404142434445464748495051525354555657

1992199319931993199419951995199519951995199519951996199619961996199619961997

10030808090509111111121202101010111201

27220303282908222223071021091010272013

1102110312 4316 3309 3804 5812 1304 1522 1618 07180103 2704 5913 1001 1004 5400 4407 2110 19

44501423373722265726015256592451252028

28.8534.7428.6228.3630.6534.8929.4929.0728.3229.3134.7934.3729.0334.5034.5834.7534.4727.7534.09

33.1234.4134.4034.0832.8032.6332.2634.7334.2134.4824.1523.3734.3732.0931.3432.0332.0333.0431.74

19.015.015.015.023.015.013.018.415.015.015.021.015.023.019.033.032.624.033.0

3.95.36.05.73.85.34.26.25.05.35.25.05.16.45.44.95.04.45.3

312343139142270224117196202199319289132481391476212397

4627361349208559677762230775362486576

-117133-122-123-140132-6-15-3712375-104170124-168-6311

ABUCMTCMTCMTABUCMTABUCMTCMTCMTCMTCMTCMTCMTCMTCMTCMTABUCMT

21

Figure Captions

Figure 1. Distribution of earthquake epicenters in the studied area for the time period1900 - 1998.

Figure 2. Distribution of earthquakes and seismogenic zones in Egypt and its vicinity(modified from Kebeasy, 1990). Numbers identify seismogenic zones mentioned inthe text.

Figure 3. (a) Focal mechanism solutions available for the studied area. The numbersin the figure are the same as in Table (3). The size of each beach ball is proportionalto the size of the earthquake, (b) Representative focal mechanism for each seismiczone.

Figure 4. (a) Regional polygons used in this study, (b) Crustal models considered foreach polygon.

Figure 5. Distribution of the computed (a) ground displacement, DMAX, (b) groundvelocity, VMAX, and (c) design ground acceleration, DGA. Both DMAX and VMAXare calculated for frequencies up to lHz.

Figure 6. Map of design ground acceleration distribution computed for the event of1996, in the Gulf of Aqaba and examples of the ground motion traces. Seismogramsare computed up to frequencies of lHz. The peak value of ground motion parametersis given above §ach trace, d = distance in km and Az = azimuth in degrees.

22

* + +• + #

Magnitude<5.0

O 5.0-5.4A 5.5-5.9# 6.0-6.4

6.5-6.97.0-7.4

Figure (1)

23

Magnitude+ <5.0

O 5.0-5.4A 5.5-5.9# 6.0-6.4

6.5-6.97.0-7.4

25° 35°

Figure (2)

24

35°

Figure (3a)

25

Figure (3b)

26

Crete Cyprus

Mediterranean Sea

Figure (4a)

27

0 2

0 10

10

•3 20

30

40

0 500 1000 1500

40

3 4

1 .

0

10

20

30

40

0 2 4 6 8

1 •

. 1 . . .

0 1 2 3 4 0 2 4 6 8V

10

20

30

40

1 •-

n .. :

IV0 1 2 3 4 0 2 4 6 8

0

0 I 2 3 4, 0 2 4 60

1•£

Q

30

20

30

40

•

•

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

n) )

•

0 500 1000 1500

L

0 500 1000 1500

L L_j

•

0 500 1000 15000

10

20

30

40

• 1 1

0 500 1000 15000

10

20

30

40

L

Qp

Qs

•

Density (g/cm3) Velocity (km/s) Q

Figure (4b)

28

Mediterranean Sea

0.5-1.01.0-2.02.0-3.53.5-7.07.0-13.4

25 30°

Figure (5a)

VMAX(cm)• 0.0-0.5

0.5-1.01.0-2.02.0-4.04.0-8.08.0-15.015.0-30.030.0-36.0

Figure (5b)

30

DGA(cm/s2). 0.000-0.005+ 0.005-0.0ld

0.010-0.02(jv 0.020-0.04Cf

0.040-0.0800.080-0.1500.150-0.300)

«. 0.300-0.338

0 +OOQO +

QOOOO+OOOOOO++OOOOO+

•j-foooo+t

Figure (5c)

31

= 657km = 469km = 290° d = 30Okm

liill/iAvV^v™^—^^-

1.56 (cm/s)

2.11 (cm/s1)

0 100 200 \ 300Time (s)

0/ 100 200 300Time (s)

0 100 200 / 300Time fs)

0.82 (cm/s)W*H

1.59 (cm/s1) 2.13 (cm/s:)

0 100 200 300Time (s)

z = 22T d = 395km

0 100 200 300Time (s)

z = 204° d = 388km

2.11 (cm/s)

0.92 (cm/s)

1.38 (cm/s1)

0 100 200 3001 line (s)

Az=188" d = 414km

Figure (6)

32