ORIGINAL PAPER

Multi-seismotectonic models, present-day seismicity and seismichazard assessment for Suez Canal and its surrounding area, Egypt

Mohamed Ahmed El-Eraki1 • Abd el-aziz Khairy Abd el-aal2 • Shaimaa Ismail Mostafa1

Received: 3 February 2015 / Accepted: 13 July 2015

� Springer-Verlag Berlin Heidelberg 2015

Abstract Suez Canal is the most important navigational

water stream in the world. It separates the eastern part of

the Nile Delta from northern Sinai and controls 40 % of

ship movement in the world. There is also the new Suez

Canal project, which is one of the most important new

projects in Egypt. The purpose of this study is to assess

seismic hazards at and around Suez Canal. The technique

used in hazard estimation is the probabilistic seismic haz-

ard approach (PSHA). Alternative seismotectonic source

models were included in the hazard assessment to account

for the epistemic uncertainty. Contour maps were produced

for ground motion on rock for spectral periods 0.2, 0.5, 1

and 2 s, as well as Peak Ground Acceleration (PGA) for

return periods of 75, 475, 975 and 2475 years (equivalent

to 20, 10, 5 and 2 % probability of exceeding ground

motion in 50 years, respectively). The Uniform Hazard

Spectra (UHS) was also estimated for some cities inside the

study area on rock for return periods of 75, 475, 975 and

2475 years. The results show that the highest hazard level

is at the southeastern part of the study area with maximum

expected spectral acceleration of 280.3 cm/s2 (gal) at a

spectral period of 0.2 s for a return period of 475 years.

The results of this study can be used for seismic micro-

zonation, seismic risk mitigation and for earthquake engi-

neering purposes.

Keywords Probabilistic seismic hazard approach �Uniform hazard spectra � Peak ground acceleration �Microzonation and seismic risk

Introduction

The study area includes the eastern part of the Nile Delta,

Suez Canal and north western Sinai (Fig. 1). The area is

characterized by a thick section of sedimentary deposits

that is prone to amplify the seismic waves in the case of an

earthquake. Suez Canal is the most important water stream

in the world. It allows ships and containers coming from

Mediterranean countries, Europe and America to reach

Asia, rather than taking the Ras El-Ragaa El-Saleh long

way. It controls 40 % of ship movement in the world and

connects the whole world. The study area was affected by

several historical and instrumental earthquakes. Therefore,

it is important to estimate its seismic hazard activity for

earthquake-resistant structure design and risk mitigation.

Seismic hazard is defined as the probability of earth-

quake occurrence or earthquake effects of a certain severity

within a specific period of time, in a given area (Coburn

and Spence 1992). In other words, it is the probability that

ground-motion amplitude exceeds a certain threshold at a

specific site. The hazard can be assessed using probabilistic

or deterministic seismic hazard approaches. In this study,

the probabilistic seismic hazard assessment (PSHA) is

chosen for performing the hazard analysis because it is

widely considered as seismology’s most valuable contri-

bution to earthquake hazard assessment (Reiter 1990;

Frankel 1995; Woo 1996; Giardini 1999; Bommer et al.

2004; Deif et al. 2009; El-Hussain et al. 2010; Rafi et al.

2013; Ur-Rehman et al. 2013a, b).

& Shaimaa Ismail Mostafa

High_Dam83@yahoo.com

1 Geology Department, Faculty of Science, Zagazig

University, Zagazig, Egypt

2 National Research Institute of Astronomy and Geophysics

(NRIAG), Helwan, Egypt

123

Bull Eng Geol Environ

DOI 10.1007/s10064-015-0774-1

PSHA was first introduced by Cornell (1968), and since

then has been widely adopted and modified (McGurie

1978; Bender and Perkins 1987). This technique uses the

most available amount of data to build up a model of

earthquake-producing processes to understand the nature of

the earth’s crust features that are causing earthquakes in a

region. It addresses the chance of failure by estimating the

chance of exceeding the design ground motion. Estimating

the chance of strong ground motion at a given level is the

most critical input for seismic zoning and building code

design.

However, there is an element of uncertainty in the

hazard calculation that needs to be factored into the cal-

culations (El-Hussain et al. 2010). The Aleatory variability

and epistemic uncertainty are used in seismic hazard

analysis, and while they are not commonly used in other

fields, the concepts are well known. Aleatory variability is

the natural randomness in a process. It is a result of our

simplified modeling of a complex process. Epistemic

uncertainty is the scientific uncertainty in the simplified

model and is characterized by alternative models. The

standard deviation of the ground motion from the modeled

values is used to account for ground motion variability. In

this study, the epistemic uncertainties are treated by taking

alternatives for the ground motion attenuation relation-

ships, which in turn implicate several different estimates of

the ground motion.

PSHA technique was applied to produce 5 % damped

spectral acceleration values on rock for peak ground

acceleration (PGA) and spectral periods of 0.2, 0.5, 1 and

2 s for return periods of 75, 475, 975 and 2475 years to

define approximate uniform hazard spectra (UHS) at each

site using a grid of 0.1� 9 0.1�. The produced seismic

hazard results are key input parameters to be used by

seismic risk studies to yield estimates of the expected

losses from earthquakes.

Geology and tectonics

Suez Canal is a very long channel connecting the Port Said

Governorate on the Mediterranean Sea to the Suez

Governorate on the Gulf of Suez, which is an extension of

Fig. 1 Location map of the

study area

Fig. 2 Structural zones of the region of the east Nile Delta (El-

Fayoumy 1968)

M. A. El-Eraki et al.

123

the Red Sea (Fig. 1). It separates the eastern part of the

Nile Delta and northern Sinai. The eastern part of the Nile

Delta is characterized by low relief and its surface gently

slopes towards the north. It takes a rolled shape to the south

and its land rises up to a moderately elevated plateau

(Bayoumy 1971; Abd El Gawad 1997).

The surface of the study area is composed mainly of

Quaternary deposits. It consists of sabkha deposits, sand

dunes, marsh, clay, silt, sand, gravel, evaporites, undiffer-

entiated Quaternary deposits, alluvial fans, wadi deposits,

recent coastal deposits and stabilized dunes that cover most

of the surface in northern Sinai. Nile silt, Neonile deposits,

prenile deposits and protonile deposits were also found on

the surface of the western bank of Suez Canal (GPC and

CONOCO 1987).

Tertiary rocks are presented on its surface by Mokattam

Group (middle Eocene), Maadi Formation (upper Eocene),

Gebel El-Ahmer Formation (Oligocene) and Hagul For-

mation (upper Miocene). However, these Tertiary rocks are

represented on the surface of the eastern bank of Suez

Canal by Maadi Formation (upper Eocene) and Gharandal

Group (lower Miocene). To the south of northern Sinai,

undifferentiated upper cretaceous deposits, including

Matulla, Wata and Halal Formations, were found to be

represented on the surface with Sudr Formation, while the

upper cretaceous rocks appear in the eastern Nile Delta at

its southwestern side, and are represented by Abu Roash

and Khoman Formation (GPC and CONOCO 1987).

The subsurface structural framework of northern Egypt

is complicated, as it lies in the unstable or mobile shelf of

the northeastern Africa (Said 1962). It was affected by the

interaction of African, Eurasian and Arabian tectonic

plates. According to El-Fayoumy (1968), the East Nile

Delta region is divided into five different structural zones,

each of them with its specific characteristics (Fig. 2):

(a) the mobile belt (at the north), (b) the hinge belt (at the

middle), (c) the metastable belt (at the south), (d) tafro-

geosyncline of the Gulf of Suez (at the east) and (e) tafro-

geosyncline of the Nile Delta (at the west).

The main structural elements of the east Nile Delta are

formed by faults and folds. Faults generally trend in two

directions, namely the NNW-SSE (Suez trend) and the

ENE-WSW trend (Syrian Arc trend). The age of NNW-

SSE faults seems to be younger than that of the older ENE

structural trend (El-Dairy 1980). The faults at the eastern

Nile Delta are of normal type and strike mainly in two

directions; these are the E-W and NW–SE directions. They

have a relatively minor importance with regard to folding

and are recorded only at a few localities on the surface,

e.g., Gebel Subrawit, Gebel Iwabid (El-Fayoumy 1968).

Northern Sinai is characterized by well-exposed NE–

SW doubly plunging folds that extend northeastward to the

Dead Sea Transform forming the major part of the Syrian

Arc System (Krenkel 1925). These folds and their associ-

ated faults were formed by dextral transpression on a set of

ENE–WSW pre-existing faults (Youssef 1968; Moustafa

and Khalil 1988, 1989; Moustafa et al. 1991; Abd El-Aal

et al. 1992).

Sinai is surrounded by the Northern Red Sea, Gulf of

Suez, Aqaba-Dead Sea and Cyprian Arc active seismic

zones. The Northern Red Sea is an active rift in the last

stages of continental rifting (Meshref 1990). It is charac-

terized by its wide main trough, which is bounded by steep

continental slopes with a general orientation of NW–SE,

except for the northernmost part, which is characterized by

an E–W slope. Most of the faults in the Suez rift strike are

grossly parallel to its trend and delimit many blocks that

Fig. 3 Seismicity and main seismic trends in East Mediterranean

region

Table 1 Focal mechanism

parameters of the 28 December

1999 earthquake and its

aftershocks (Abd El-Aal 2010b)

Earthquake date Coordinates Magnitude (Mw) Focal mechanism Remarks

Latitude Longitude Strike Dip Rake

28 Dec 1999-M 30.29 31.45 4.5 137 72 -39 Mainshock

28 Dec 1999-AF1 30.25 31.5 3 130 70 -35 Aftershock

28 Dec 1999-AF2 30.26 31.44 3.2 140 75 -37 Aftershock

Multi-seismotectonic models, present-day seismicity and seismic hazard…

123

are usually tilted. The border faults are the most obvious

faults that separate the intensely faulted blocks from the

uplifted shoulders, which were slightly affected by the rift

faulting (Colletta et al. 1988).

Aqaba Dead Sea system is a left lateral strike slip fault

that consists of en echelon faults with extensional jogs. The

main faults of this system are trending N-S to NNE–SSW

(Heimann and Ron 1987). Cyprian Arc lies between the

African and Eurasian plates. Its western part is highly

deformed and seismically active, and may confirm the

postulation of transcurrent fault (Wong et al. 1971; Maa-

moun et al. 1980; Ben-Avraham and Nur 1986). Seismic

activity and gravity anomalies indicate that the northward

subduction of the African plate beneath the Turkish Plate is

the mode of convergence along the western segment of the

Cyprian Arc (Ben-Avraham et al. 1988).

Seismicity

Seismicity is the study of the distribution of earthquakes

and their characteristics within a particular region. It is

important in the assessment of seismic hazards for a defi-

nite region. In Egypt, seismicity is due to the interactions

between African, Arabian, and Eurasian plates and the

Sinai sub-plate. The activity tends to occur along seismic

trends (Fig. 3): Gulf of Suez rifting, Levant-Aqaba trend,

Red Sea rifting and Mediterranean coastal dislocation

trend.

Egypt is considered to be one of the few regions in the

world where evidence of historical earthquake activity has

been documented during the past 4800 years. Many events

were reported to have occurred in and around Egypt, and to

have caused damage of variable degrees in different

Fig. 4 Seismicity and seismotectonic source model (option 1) Fig. 5 Seismicity and seismotectonic source model (option 2)

Fig. 6 Seismicity and seismotectonic source model (option 3)

M. A. El-Eraki et al.

123

localities; these include: 2200 BC (Sharkia province

earthquake) and 27 January 859 AD (Belbeis earthquake)

(Ambraseys 1961; Maamoun 1979; Ibrahim and Marzouk

1979; Poirier and Taher 1980; Savage 1984; Kebeasy 1990;

Ambraseys et al. 1994).

Concerning recent earthquake activity in Egypt, the

recording of earthquakes started in 1899 with the Helwan

station. The instruments of this station have been upgraded

several times. The Egyptian National Seismological Net-

work consists of 66 seismic stations covering all the known

seismic sources in Egypt (Abd el-aal 2013; Abd el-aal and

Samy 2013). The study area was affected by several

earthquakes of variable magnitudes. The epicenter of the

28 December 1999 earthquake and its aftershocks

(Table 1) occurred in the Abu Zabal seismic zone. The

epicentral area was affected by three normal fault trends in

the E–W, NW–SE, and NE–SW directions. Abu-Hammed

Table 2 Seismicity recurrence parameters for seismotectonic source

model (option 1)

Zone Mmax Mmax obs. Mmin b b k

1 5.72 5.22 3.5 1.47 0.64 3.175

2 6.02 5.52 3 2.95 1.28 9.444

3 4.88 4.62 3 2.15 0.93 3.565

4 6.89 6.7 3 1.85 0.81 1.293

5 4.9 4.72 3 1.57 0.68 1.936

6 6.19 5.9 3 1.84 0.8 0.198

7 4.92 4.42 3 3.35 1.46 5.504

8 4.38 4.22 3 3.2 1.39 7.105

9 4.92 4.42 3 3.2 1.39 2.637

10 5.41 5.03 3 2.22 0.97 2.854

11 4.95 4.17 3 2.16 0.94 1.601

12 6.5 6 3 1.93 0.84 0.092

13 4.92 4.42 3 2.66 1.15 1.182

14 6.54 6.33 3 1.26 0.55 0.162

15 4.72 4.22 3 2.7 1.17 1.158

16 6.24 6.05 3 1.14 0.5 13.677

17 5.41 5.03 3 1.5 0.65 6.351

18 5.07 4.65 3 1.39 0.6 1.673

19 7.34 7.21 3 1.15 0.5 21.745

20 6.4 6.33 3 1.38 0.6 12.15

21 7.02 6.92 3 1.15 0.5 60.269

22 5.42 5.37 3 1.27 0.55 7.872

23 5.3 5.2 3 1.19 0.52 2.329

24 5.7 5.62 3 1.15 0.5 3.224

25 5.79 5.67 3 1.18 0.51 1.041

26 6.53 6.1 3 1.22 0.53 0.066

27 6.62 6.12 3 1.35 0.58 1.234

28 5.92 5.54 3 1.46 0.63 2.565

29 6.71 6.21 3 1.57 0.68 1.618

30 6.76 6.51 3 1.16 0.51 2.339

31 6.8 6.72 3 1.15 0.5 13.352

32 5.19 5.12 3 1.2 0.52 3.431

33 6.03 5.96 3 1.22 0.53 6.341

34 7 6.91 3 1.1 0.48 5.182

35 6.79 6.71 3 1.14 0.5 29.769

36 8.01 7.9 3 1.18 0.51 30.08

37 7.13 7.01 3 1.23 0.53 7.039

38 4.64 4.12 3 1.74 0.76 1.752

Back ground 4.74 4.62 3 2.18 0.95 4.65

Table 3 Seismicity recurrence parameters for seismotectonic source

model (option 2)

Zone Mmax Mmax obs. Mmin b b k

1 5.95 5.52 3 2.7 1.17 11.299

2 4.84 4.62 3 2.19 0.95 4.181

3 6.88 6.7 3 1.81 0.79 1.215

4 4.84 4.68 3 1.89 0.82 3.026

5 6.46 6.33 3 1.29 0.56 0.165

6 5.26 5.03 3 2.57 1.12 7.496

7 4.58 4.42 3 3.32 1.44 12.052

8 5.87 5.4 3 2.86 1.24 0.347

9 7.31 7.21 3 1.05 0.46 17.429

10 7.01 6.92 3 1.1 0.48 27.117

11 5.42 5.37 3 1.32 0.57 7.065

12 5..9 5.82 3 1.07 0.47 2.814

13 6.52 6.3 3 1.2 0.52 0.092

14 6.51 6.21 3 1.33 0.58 4.043

15 6.8 6.72 3 1.07 0.47 17.07

16 7.39 7.3 3 1.09 0.48 5.148

17 7.92 7.9 3 1.09 0.47 4.387

Back ground 6.15 5.62 3 2.11 0.92 5.493

Table 4 Seismicity recurrence parameters for seismotectonic source

model (option 3)

Zone Mmax Mmax obs. Mmin b b k

1 5.79 5.52 3 2.54 1.1 9.648

2 6.91 6.7 3 1.67 0.73 0.77

3 6.46 6.33 3 1.29 0.56 0.165

4 7.31 7.21 3 1.06 0.46 19.057

5 6.8 6.72 3 1.13 0.49 1.091

6 7.91 7.9 3 1.06 0.46 5.034

7 5.93 5.62 3 2.54 1.1 0.455

Back ground 6.13 5.79 3 2.7 1.17 0.744

Multi-seismotectonic models, present-day seismicity and seismic hazard…

123

earthquake (29 April 1974) was located at 31.63�E and

30.59�N, with moment magnitude (Mw) equal to 5.11. It

was affected by two planes trending ENE–WSW and

NNW–SSE, with left lateral strike-slip motion along the

second plane (Mousa 1989; Hassib 1990). Ismailiya

earthquake, 1987 (Mw = 5.28) was located at 32.22�E and

30.46�N. It was affected by strike-slip with two nodal

planes trending N 68�E and S 24�E, with an 80� dip angle

for both (Megahed and Dessoky 1988).

Gulf of Suez was affected by several earthquakes and is

characterized by different levels of seismic activities. The

highest seismic activity is at its southern end. Its importance

comes from the presence of earthquake swarms. The

mechanism of faults responsible for the earthquakes at

Shadwan Island [31 March 1969 (MW = 6.9)] are normal

faulting with the T-axis perpendicular to the strike of the

Gulf. The 1969 earthquake was preceded by 35 large fore-

shocks during the last half of March 1969, and was followed

by a large sequence of aftershocks (Kebeasy 1990). Another

swarm in the southern Gulf of Suez, recorded at Gubal

Islands, shows reverse faulting with theP-axis perpendicular

to the strike of the Gulf (Hurukawa et al. 2001).

The Gulf of Aqaba is characterized by a high level of

seismic activity. A number of seismic swarms occurred in

this zone, such as the 1983 earthquake swarm. More than

500 events were recorded from 21 January up to 20 April.

Another earthquake swarm occurred from August 1993 up

to February 1994. The strongest event of this swarm

occurred on 3 August 1993 (MW = 6.1), and was followed

by more than 600 events (El-Rayess 2010). The largest

earthquake in the Gulf of Aqaba occurred on 22 November

1995 (MW = 7.3). This earthquake caused widespread

damage in the surrounding area, with an extending effect

reaching Cairo city (El-Hadidy et al. 1998). In November

2002, an earthquake swarm took place at the middle of the

Gulf. These earthquake swarms indicate that the Gulf of

Aqaba has been the most active part during the last two

decades, and correlate with the field evidence of recent

activity (Garfunkel 1974; Ben-Avraham et al. 1979; Eyal

et al. 1981).

Input for PSHA in the area of interest

To perform PSHA calculation at a given site, the following

input parameters are needed (Cornell 1968; McGuire 1976;

Reiter 1990):

1. An earthquake catalogue.

2. A seismotectonic source model.

3. Seismicity recurrence characteristics for the seismic

sources, where each source is described by an earth-

quake recurrence relationship. This relationship

indicates the chance of an event of a given size to

occur anywhere inside the source zone during a

particular period of time. A maximum earthquake is

chosen for each seismic source, representing the

largest event to be considered.

4. A predictive ground motion model describes the

attenuation of amplitudes of ground motion as a

function of distance and magnitude. Different models

are constructed for different frequencies and local

tectonic site conditions.

Earthquake catalogue

The starting point for seismic hazard assessment is

preparing an earthquake catalogue. This catalogue contains

information about the location, time of occurrence, size and

depth of earthquakes. The seismic data used in this study

includes updated earthquake catalogues. All the available

data from many catalogues were gathered and compiled in

one catalogue including historical (from 93 AD to 1899)

and instrumental (from 1900 to 2011) earthquake data.

The instrumental earthquake data were gathered from

the International Seismological Center Bulletin (ISC)

(http://www.isc.ac.uk/), data collected by the European

Mediterranean Seismological Center (EMSC) (http://www.

emsc-csem.org); Preliminary Determination of Epicenters

‘‘online bulletin provided by the National Earthquake

Information Center (NEIC) for the period from 1900 to

2007’’ (http://earthquake.usgs.gov/earthquakes/); Aswan

seismic Bulletin, Egyptian Research Institute of Astronomy

and Geophysics (www.nriag.sci.eg); Bulletins of the

Egyptian National Seismic Network for events that

occurred after 1997 in Egypt and its surrounding area;

Catalogue provided by the Aswan Regional Seismic Center

starting from 1982, and published data from Maamoun

et al. (1984), Abd el-aal 2008, 2010a, b and Abd el-aalet al.

(2015). Also, published data on historical earthquakes were

also considered (Ambraseys 2001; Ambraseys et al. 1994).

Any duplication of events in the resultant catalogue was

removed and only events with magnitude C3 were selected

to perform the analysis. All events in this catalogue are in

moment magnitudes scale, which is the most reliable

magnitude scale. Also, dependent events (foreshocks and

aftershocks) were removed (catalogue declustering) to

satisfy the spatial and temporal principles of earthquakes

independency. The resultant total number of dependent

events is 10,640 events.

Seismotectonic models

Seismotectonic source model is defined as the geographic

distribution of seismic sources and the specification of all

M. A. El-Eraki et al.

123

Fig. 7 Seismic hazard on rock for seismotectonic source model (option 1) for spectral periods of 0.2, 0.5, 1 and 2 s, as well as PGA (a, b, c,d and e, respectively) for 475-year return period

Multi-seismotectonic models, present-day seismicity and seismic hazard…

123

source characteristics required for the seismic hazard

analysis (Abd el-aalet al. 2015; El-Hussain et al. 2010). A

source zone can be idealized as a point source, line

source, area source, volume source or dipping plane (Lee

and Trifunace 1985). The seismotectonic model was

constructed here as an area source where every point has

the same probability of being the epicenter of a future

earthquake. The model was constructed on the basis of

geology, structure, tectonics, seismicity and geophysical

studies.

In this study, 38 seismic source zones were defined, as

well as a background seismic zone, which was defined to

model the floating earthquakes that are located outside

these distinctly defined source zones (Fig. 4). For hazard

computation in the current study, two additional seismo-

tectonic source models were used (Figs. 5, 6). The alter-

native models were included in the hazard assessment to

account for the epistemic uncertainty.

To model the seismicity in each zone, we need knowl-

edge of the magnitude of completeness (Mc) below which

only a fraction of all events in a magnitude bin are detected

by the network (Stepp 1972; Kijko and Graham 1999;

Rydelek and Sacks 2003; Wiemer and Wyss 2000, 2003).

The cumulative number of events in each bin versus time

was plotted going backward from the time of most recent

event. The time at which the slope of the cumulative plot

begins to noticeably decline was identified as the com-

pleteness level of the catalogue.

Seismicity recurrence parameters

The seismicity of a seismogenic zone is quantified in terms

of the following relationship:

logNðMÞ ¼ a� bM

where N is the number of earthquakes of magnitude M or

greater per year, a is the activity and defines the intercept

of the above recurrence relationship at M equals zero

(Gutenberg and Richter 1944) and b is the slope, which

defines the relative proportion of small and large

earthquakes.

The Gutenberg and Richter (1944) relationship impo-

ses the unrealistic assumption that the maximum potential

earthquake for any region under consideration is

unbounded and unrelated to the seismotectonic setting.

All seismic zones were assumed to generate earthquakes

according to a doubly bounded exponential distribution

(Cornell and Vanmarcke 1969). The following truncated

exponential recurrence relationship is therefore commonly

used:

N �Mð Þ ¼ aexp �b M �Mminð Þ½ � � exp½ðMmax�MminÞ�

1� exp½�bðMmax�MminÞ�

where a = N(Mmin), Mmin is an arbitrary reference mag-

nitude, Mmax is an upper bound magnitude where

N (m) = 0 for M[Mmax, and b = b ln10.

The maximum likelihood procedure of Wichert (1980)

was used to obtain the parameters of the doubly bounded

exponential distribution of the seismogenic zones. This

procedure can be used to estimate the activity parameters band k (the number of occurrences per year of a hazardous

event) where there are varying levels of completeness in

the catalogue, like the current catalogue case.

It is important to define the maximum earthquake for

each seismic zone. This is because it has a considerable

influence on the hazard, especially at long return periods

and short distances from the site of interest. Regression

relationships between earthquake magnitude and fault

parameters have been developed in the past several decades

(Slemmons 1977; Bonilla et al. 1984; Wells and Copper-

smith 1994; Hanks and Bakun 2002). Many studies have

been done to estimate the maximum magnitude using fault

parameters (e.g., Slemmons 1982; Berberian and Yeates

1999; Wells and Coppersmith 1994). The methods avail-

able for estimating Mmax can be classified according to

four procedures: (1) in the case of the presence of paleo-

seismological studies, the results of these studies indicate

the maximum magnitude; (2) when the seismic history is

available, the maximum magnitude is estimated using the

statistical procedure proposed by Kijko (2004); (3) when

consistent data regarding fault type and its total length are

available, it is assumed that portions from 20 to 40 % of

the total fault length could rupture in one earthquake and

then the maximum magnitude is estimated; (4) in any

remaining case, the maximum magnitude is estimated by

adding 0.5 magnitude units to the largest known magnitude

in the zone. In this study, procedures 3 and 4 have been

used for estimating the maximum magnitude Mmax for each

seismic zone and fault.

The recurrence parameters were obtained using

MATLAB code AUE program (Kijko 2004). This program

was used for estimating the recurrence parameters. It takes

into account both the incompleteness of the seismic cata-

logue and the temporal variation of seismicity. It could

estimate the area characteristic seismic hazard parameters:

Mmax, k, and the b-value of Gutenberg–Richter (Tables 2, 3and 4).

Predictive ground motion models

Seismic hazards assessment requires the prediction of

strong ground motion from earthquakes. Theoretical

models have been developed for the estimation of ground

motion prediction equations (attenuation models) and

simulation of time series. In hazard analysis, a ground

M. A. El-Eraki et al.

123

Fig. 8 Seismic hazard on rock for seismotectonic source model (option 2) for spectral periods of 0.2, 0.5, 1 and 2 s, as well as PGA (a, b, c,d and e, respectively) for 475-year return period

Multi-seismotectonic models, present-day seismicity and seismic hazard…

123

Fig. 9 Seismic hazard on rock for seismotectonic source model (option 3) for spectral periods of 0.2, 0.5, 1 and 2 s, as well as PGA (a, b, c,d and e, respectively) for 475-year return period

M. A. El-Eraki et al.

123

motion model is used to predict accelerations from the

complete spectrum of magnitude and distance. The scarcity

and lack of ground motion acceleration records in Egypt

makes it necessary to apply already developed ground

motion scaling relationships.

In the present study, the hazard was calculated in terms

of peak ground acceleration (PGA) and response spectrum.

PGA is the most widely used and simplest strong motion

parameter. Response spectrum is the most important

characterization of ground motion in earthquake engi-

neering (El-Hussain et al. 2010). Abrahamson and Silva

(1997) and Youngs et al. (1997) models were applied in

terms of Mw to compute ground motion for rock site

Fig. 10 UHS on rock at some cities for return periods of 75, 475, 975 and 2475 years (a, b, c and d, respectively) for seismotectonic source

model (option 1)

Fig. 11 UHS on rock at some cities for return periods of 75, 475, 975 and 2475 years (a, b, c and d, respectively) for seismotectonic source

model (option 2)

Multi-seismotectonic models, present-day seismicity and seismic hazard…

123

conditions. These models were used in comparison to each

other to ensure the accuracy of the results.

PSHA was performed using CRISIS 2007 software

(Ordaz et al. 2007). This program accommodates for the

effect of the aleatory uncertainty in the hazard computation

by specifying bounds for the recurrence parameters, the

maximum magnitude of each seismogenic zone and the

predicted ground motions. It uses tabulated ground motion

values to define the level of ground motion corresponding

to a particular magnitude distance scenario. The distance

metrics are handled in a straightforward manner using the

software package CRISIS 2007. It also facilitates the

Poisson occurrence model characteristics; this model was

chosen to be the model for the occurrence of ground

motion at a specific site.

Method

The PSHA technique uses the largest possible amount of

data, combining seismological, geological and geophysical

data to build up a model of the earthquake-producing

processes. The probability that the value Z will be excee-

ded within t years is given by the equation:

Pt zð Þ ¼Xk

j¼1

Zm¼Mmax

m¼Mmin

Pt mð ÞZRmax

r¼R0

P rð Þ P A� Zð Þm; rð Þdmdr

where j is a seismogenic zone, m is the magnitude, Pt (m) is

the probability of occurrence of a magnitude m earthquake

in zone j within t years Pt mð Þ ¼ 1� exp �tnðmÞ

h ih i, r is the

distance to the energy source, P (r) is the probability that

the earthquake of magnitude m in zone j will occur at a

distance r from the analyzed site/geographical point, and

P (A C Z) is the probability that given the magnitude of the

earthquake and the distance to the source, the ground

motion A at the site will exceed the ground motion level

Z. This equation is based on the assumption that the ran-

dom temporal occurrence of the earthquakes in zone j obey

Poisson distribution laws (Abd el-aal et al. 2012).

PSHA results

Probabilistic seismic hazard assessment was conducted in

the area of study through a grid of 0.1� 9 0.1�. Three

alternative seismotectonic source models were used to

account for the epistemic uncertainty. Abrahamson and

Silva (1997) and Youngs et al. (1997) attenuation relations

models were used in comparison to each other to ensure the

accuracy of the results. Seismic hazard was conducted for

return periods of 75, 475, 975 and 2475 years. Only the

results of the return period of 475 years are presented here.

The results of the two attenuation models were very

close to each other, implying the accuracy of the estimates.

Only the results using the Youngs et al. (1997) attenuation

model are presented here. Also, the results of the alterna-

tive seismogenic source models are presented. Contour

maps were graphed for PGA and spectral periods of 0.2,

0.5, 1 and 2 s (Figs. 7, 8 and 9) for rock site conditions.

Fig. 12 UHS on rock at some cities for return periods of 75, 475, 975 and 2475 years (a, b, c and d, respectively) for seismotectonic source

model (option 3)

M. A. El-Eraki et al.

123

The hazard maps revealed that the most hazardous region is

located at the southeastern part of the study area. This is

consistent with the tectonic setting of the area where this

region is affected by the triple junction between the Afri-

can, Eurasian and Arabian plates and the Sinai subplate.

The results are presented in terms of uniform hazard

spectra (UHS) for six important cities inside the study area.

These cities are Port Said, Ismailia, Suez, Cairo, Zagazig

and Damietta. UHS was estimated on rock sites for return

periods of 75, 475, 975 and 2475 years. These return

periods correspond to 20, 10, 5 and 2 % probability of

exceeding ground motion in 50 years period (which is the

expected design life for a building). The 475-year return

period event is the most common standard used in the

industry for assessing seismic risk, and it is also the basis

for most building codes for seismic design. UHS computes

the hazard at a suite of spectral periods using response

spectral attenuation relationships. The results of UHS

(Figs. 10, 11 and 12) show that the most hazardous region

in the study area is Suez city, whereas the lowest values are

shown towards the north at the Mediterranean Sea in the

cities of Port Said and Damietta.

Conclusion

This study highlights the degree of seismic hazards related

to earthquake activities in the study area (including the

cities of Port Said, Ismailia, Suez, Cairo, Zagazig and

Damietta). The hazard maps denote ground motion on

rock. Thus, the current analysis did not consider the

amplification of soil or basin response. Historical and

instrumental database were incorporated in the analysis,

and their magnitudes were converted to a uniform moment

magnitude scale. The definition of the boundaries of the

seismotectonic source zones was carried out depending on

the existing geological, structural, tectonic, seismological

and geophysical data. The geometry of the seismogenic

zone pattern affected the hazard results.

PSHA results are based on the assumption that in the

future, the location of major seismic activity will be

essentially limited to the restrictedly defined seismic zones.

The effect of uncertainty was taken into consideration

through the use of alternative seismotectonic source mod-

els and different ground motion relations. The application

of two different attenuation models in comparison to each

other gave very close results, confirming the stabilization

of the results.

Contour maps of peak ground acceleration and 0.2, 0.5,

1 and 2 s spectral accelerations for rock conditions for a

return period of 475 years were made. The computations

were made for points distributed on a grid at 0.1� intervalsin both directions, and this defines the spatial distribution

of the maps. Almost all the hazard maps, and even the long

period one (2 s), have the same features. The effect of the

background zones for the area of interest on the hazard

results is almost negligible, as it combines areas of very

low to moderate seismic activities. These maps highly

reflect the general tectonic setting of the studied area. The

highest activity is shown at the southeastern part of the area

of study and decreases towards the north direction.

The results of the present study have been compared

with the results of previous studies of seismic hazards in

northern Egypt and are found to be close. The UHS results

reflect the ground shaking at each period. These results

could be used to assess the chance of failure by estimating

the chance of exceeding the design ground motion, and in

some cases, by estimating the probability of failure of the

structure using probabilistic risk analysis.

Acknowledgments The authors thank the Egyptian National Seis-

mic Network, which provided the earthquake catalogues and soft-

ware. Figures were generated by ARC GIS and Golden software

(Surfer and Grapher).

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