1. AN UPDATED SEISMIC HAZARD ASSESSMENT FOR EGYPT
EIGHTH INTERNATIONAL CONFERENCE
ASSIUT
ON THE GEOLOGY OF AFRICA
AN UPDATED SEISMIC HAZARD ASSESSMENT FOR EGYPT
Rashad Sawires1,2*, José A. Peláez2,
Raafat E. Fat-Helbary3, and Hamza A. Ibrahim1.
1 Geology Department, Assiut University, Assiut, Egypt.
2 Department of Physics, University of Jaén, Jaén, Spain.
3 Aswan Regional Earthquake Research Centre, Aswan, Egypt. *

2. Motivation of the study Declustered shallow seismicity (h ≤ 35 km).
Largest instrumental events (magnitudes equal or above MW 5.0) that have been taken place in Egypt in the last 50 years.

3. Motivation of the study
ECP-201 (2011) is still depending on a seismic hazard assessment that do not consider neither the historical earthquake events nor an up-to-date earthquake catalogue and seismic source model.
(ECP-201, 2011)
Thus, there is an urgent need to estimate up-to-date seismic hazard values and to supply this information for application and use in improving seismic zoning maps and building design and construction.
Seismic hazard zoning map for Egypt (modified after ECP-201: 2011 and Riad et al., 2000).

4. Objectives/ METHODOLOGY
Seismic hazard is defined as the probability of occurrence of an earthquake or earthquake effects of certain severity, within a specific period of time, in a given area.
An earthquake recurrence model that describes the recurrence of events in time within the seismic source zones.
The overall purpose of this work was to carry out a probabilistic seismic hazard assessment for Egypt, in terms of mean horizontal peak ground acceleration (PGA), and spectral acceleration (SA) values.
The output results could be used to modify and update the seismic action in the upcoming building codes.
A seismic source model that defines the spatial distribution of earthquakes within the region of concern.
A ground-motion attenuation model that describes mathematically the manner in which earthquake ground-motions decrease with distance from an earthquake source for various magnitude levels.
A probability model for calculating the expected maximum amplitude of ground-motion within a given period of time corresponding to a chosen probability level.
Schematic description of the classical PSHA methodology.

5. Data and methodology
1. A Seismic Source Model

6. 2. An Earthquake Recurrence Model
Data and methodology
2. An Earthquake Recurrence Model
b-values, annual rates of earthquakes, approximate completeness periods, and maximum observed and expected magnitudes for the delineated seismic sources.
(*) The most recent event, (**) Macroseismic surface-wave magnitude (after Ambraseys et al., 1994).
A Calculated using Robson-Whitlock-Cooke procedure.
B Equal to maximum recorded magnitude.
C Taken from Deif et al. (2009, 2011).

7. 3. Ground-Motion Attenuation Equations
Data and methodology
3. Ground-Motion Attenuation Equations
GMPE
Region
Magnitude
Type and Range
Distance
Definition (km)
Spectral
Period
Site Conditions
Faulting
Mechanism
Horizontal
Component
Definition
Ambraseys
et al. (1996)
Europe +
Middle East MS
( )
rjb
(0 – 200)
PGA,
0.1 – 2.0 s
Rock (VS ≥ 750 m/s),
Stiff Soil (750 ≤ VS < 360 m/s),
Soft Soil (360 ≤ VS < 180 m/s),
Very Soft Soil (VS ≤ 180 m/s).
Not Considered
Larger
Abrahamson and Silva
(1997)
Worldwide MW
(4.4 – 7.4)
rrup
(0 – 220)
0.01 – 5.0 s
Rock/ Shallow Soil (VS > 600 m/s)
Deep Soil (VS < 150 m/s)
Reverse/
Oblique-slip/
Others
Average
Zhao
et al. (2006)
Japan
( )
(0 – 300)
0.05 – 5.0 s
Rock (VS ≥ 600 m/s),
Hard Soil (600 ≤ VS < 300 m/s),
Medium Soil (300 ≤ VS < 200 m/s),
Soft Soil (VS ≤ 200 m/s).
Normal/
Strike-slip/
Unspecified
Geometric
Mean
Boore and Atkinson
(2008)
California +
Taiwan
(4.27 – 7.9)
(0 – 280) s
NEHRP B (VS ≥ 760 m/s),
NEHRP C (760 ≤ VS < 360 m/s),
NEHRP D (360 ≤ VS < 180 m/s),
NEHRP E (VS ≤ 180 m/s). Cont. Function.
Tavakoli and Pezeshk
(2005)
Eastern North
America
(5.0 – 8.2)
(0 – 1000)
0.05 – 4.0 s
Hard-rock Sites
Youngs
et al. (1997)
(8.5 – 550.9)
0.075 – 3.0 s
Rock (VS > 750 m/s),
Soil (VS ≤ 750 m/s).
Interface/ Inslab
Characteristics of the considered GMPEs in the present study.

8. Data and methodology 4. Sensitivity Analysis
PGA (for a return period of 475 years) corresponding to different values of Mmax for the selected cities.
PGA values (for a return period of 475 years) corresponding to different values of beta for the selected cities.
PGA values (for a return period of 475 years) corresponding to different values of activity rates for the selected cities.
PGA (for a return period of 475 years) corresponding to applying different GMPEs for the selected cities.
Administrative map of Egypt showing the geographical distribution of the selected cities considered in the hazard computations.

9. 4. Logic-tree Formulation
Data and methodology
4. Logic-tree Formulation
Logic trees were originally introduced as a tool for treating uncertainties when performing seismic hazard assessment by Kulkarni et al. (1984).
Nowadays, logic trees are widely used for seismic hazard analysis and have become a standard feature of PSHA (Coppersmith and Youngs, 1986; Reiter, 1990; Bommer et al., 2005).
Cheng et al. (2007)
Aldama-Bustos et al. (2009)
Petersen et al. (2008)
Sutiwanich et al. (2012)
Kolathayar and Sitharam (2012)
Logic-tree framework applied in the present study.

10. SEISMIC HAZARD COMPUTATIONS
The computations was performed using the CRISIS 2014 software code (Ordaz et al., 2014) for grid points covering the Egyptian territory at a spacing of 0.1° x 0.1° (about 10 km x 10 km).
The final seismic hazard for Egypt were computed for both rock and stiff-soil site conditions for mean PGA and for 5% damping SA at 0.1, 0.2, 0.3, 0.5, 1.0, 1.5 and 2.0 s spectral periods, with a 39.3%, 10% and 5% probability of exceedance in 50 years, which correspond to return periods of 100, 475 and 975 years, respectively.

11. For a return period of 475 years
SEISMIC HAZARD RESULTS
Region
For a return period of 475 years
Significant Events
Rock site
Stiff-soil site
PGA SA
(0.1 s)
(0.2 s)
Gulf of Aqaba
0.36 g
0.89 g
0.76 g
0.41 g
0.93 g
0.97 g
MW 7.2, November 22, 1995
mb 5.8, August 3, 1993
Aswan region
0.30 g
0.71 g
0.64 g
0.34 g
0.75 g
0.81 g
MS 5.6, November 14, 1981
ML 5.6, April 23, 1982
Gulf of Suez/
Southern Sinai
0.19 g
0.50 g
0.40 g
0.23 g
0.52 g
MS 6.9, March 31, 1969
mb 5.7, June 28, 1972
Red Sea
(Abu Dabbab)
0.48 g
0.39 g
0.22 g
0.49 g
MS 5.3, November 12, 1955
mb 5.1, July 2, 1984
Surroundings
of Cairo
0.14 g
0.35 g
0.31 g
0.17 g
0.38 g
0.37 g
MS 5.9, October 12, 1992
of Alexandria
0.09 g
0.20 g
0.11 g
0.24 g
0.25 g
mb 6.5, September 12, 1955
MW 5.2, June 27, 2015

12. SEISMIC HAZARD RESULTS
UHS, damped at 5%, for different locations and for rock and stiff-soil site conditions, for the different computed return periods.

13. SEISMIC HAZARD RESULTS
City
Soil
100 years
475 years
975 years
PGA
(g)
SAmax
Tmax
(s)
0.2 s
SA (g)
1.0 s
Nuweiba R
0.156
0.382
0.1
0.331
0.063
0.294
0.742
0.642
0.146
0.383
0.978
0.848
0.204 S
0.178
0.406
0.404
0.076
0.332
0.806
0.2
0.175
0.433
1.000
0.1/0.2
0.245
Aswan
0.093
0.222
0.202
0.043
0.189
0.456
0.417
0.105
0.252
0.617
0.563
0.149
0.106
0.246
0.052
0.213
0.514
0.124
0.284
0.703
0.176
El-Tur
0.085
0.211
0.184
0.036
0.174
0.434
0.365
0.077
0.235
0.593
0.493
0.097
0.227
0.223
0.044
0.198
0.459
0.457
0.091
0.267
0.625
0.126
Sharm
El-Sheikh
0.082
0.212
0.173
0.029
0.145
0.392
0.304
0.055
0.182
0.508
0.386
0.072
0.095
0.231
0.035
0.165
0.413
0.065
0.206
0.530
0.496
0.084
NEW
Capital
0.154
0.137
0.030
0.142
0.348
0.299
0.197
0.487
0.411
0.166
0.037
0.159
0.367
0.078
0.219
0.108
Hurghada
0.070
0.177
0.150
0.027
0.134
0.349
0.286
0.054
0.463
0.373
0.080
0.190
0.032
0.371
0.360
0.064
0.199
0.474
Fayoum
0.060
0.130
0.283
0.058
0.186
0.461
0.390
0.160
0.033
0.153
0.354
0.351
0.071
0.488
0.100
CAIRO
0.324
0.280
0.062
0.441
0.379
0.086
0.167
0.148
0.075
0.475
0.104
Suez
0.151
0.131
0.285
0.443
0.388
0.090
0.164
0.353
0.201
0.484
0.107
6th of
October
0.061
0.133
0.028
0.310
0.268
0.059
0.163
0.162
0.141
0.334
0.450
0.099
Zagazig
0.125
0.122
0.305
0.261
0.067
0.155
0.139
0.325
0.442
Seismic hazard values obtained at the selected cities for the three computed return periods and for both types of soil site conditions.

14. Mean PGA values (g) for selected cities.
PRESENT STUDY
ECP-201 (2004, 2008, 2011)
Study
ECP-201 (2004, 2008 and 2011)
The current work
Matruh
0.13
0.05
Alexandria
0.09
El-Arish
0.03
Cairo
0.15
Suez
Nuweiba
0.20
0.29
Sharm El-Sheikh
Hurghada
0.25
Assiut
0.10
0.07
Aswan
0.19
Possible Causes for differences:
The unified earthquake catalogue.
The seismic source model.
Ground-Motion attenuation models.
Application of logic-tree approach.
Mean PGA values (g) for selected cities.

15. Summary and Conclusions
Eighty-eight seismic sources covering the seismic activity (shallow and intermediate-depth) in different tectonic regions have been proposed. Seismicity parameters (b-values and activity rates) have been estimated for the defined seismic sources. In addition, the maximum expected magnitude for each seismic source was computed.
A sensitivity analysis is also performed in order to evaluate the effect of different input parameters on the computed seismic hazard level.
Six well-known Ground-motion attenuation models were selected in the current study to account for the epistemic uncertainty associated with not knowing the true attenuation characteristics of the region.
Uncertainties in Gutenberg-Richter b-values, Mmax values and the GMPEs have been incorporated in the seismic hazard assessment using a logic-tree framework.
The seismic hazard has been computed using the well-known total probability theorem, for both rock and stiff-soil site conditions, and for mean PGA and SA at 0.1, 0.2, 0.3, 0.5, 1.0, 1.5 and 2.0 s, for return periods of 100, 475 and 975 years.

16. Summary and Conclusions
The seismic hazard maps and the UHS delineate the Gulf of Aqaba region with relatively higher seismic hazard from the rest of the country, which is characterized by its relatively moderate hazard levels. This region was experienced the biggest recorded earthquake since 1900 (MW 7.2, November 22, 1995 Aqaba event).
Other seismic hazard nuclei appear in the surroundings of Nasser’s Lake, in the southern part of the Gulf of Suez, at the western coast of the Red Sea near the city of Marsa Alam, in the Greater Cairo region, and in the surroundings of Alexandria.
A comparison of the computed hazard values with those considered ones in the most recent Egyptian building code has been performed. Differences were noticed especially for some very important cities (e.g., Nuweiba and Aswan).
It is concluded that a change in the seismic hazard representation of the current Egyptian building code is required in terms of the definition of the seismic hazard zoning maps, seismic hazard values, and new definition of the elastic response spectra for each city.

17. AN UPDATED SEISMIC HAZARD ASSESSMENT FOR EGYPT