Seismic hazard in terms of peak ground acceleration and spectral acceleration values, have been computed for the first time in Egypt using both historical and instrumental earthquake data. For this purpose, an updated and unified earthquake catalogue, spanning the time period from 2200 B.C. to 2013, has been prepared for Egypt and its surrounding region. Moreover, new seismic source model includes the seismic activity in and around Egypt, consisting of a total of 88 seismic zones (for shallow- and intermediate-depth seismicity) has been considered in the current assessment.
The seismicity parameters (b-value, activity rate, and maximum expected magnitude) have been computed for the delineated seismic sources. Six well-known ground motion prediction equations were selected to model the ground motion attenuation for the different tectonic environments in Egypt. A logic tree design was setup, after a sensitivity analysis, to consider the epistemic uncertainty in the Gutenberg-Richter b-value, maximum possible magnitude, and the selected ground motion prediction equations.
Seismic hazard computations, for both rock and stiff soil site conditions, with 39.3%, 10% and 5% probability of exceedance in 50 years (return periods of 100, 475 and 975 years, respectively) were performed. Thus, both PGA values for all the territory and uniform hazard spectra for selected cities among the most important and populated ones in Egypt, were computed and compared with those values considered in the most recent Egyptian building code.
From the seismic hazard maps, as well as the uniform hazard spectra, it can be noticed that the maximum hazard values are observed at Nuweiba (Gulf of Aqaba), specifically around the epicentral location of the biggest earthquake event located in Egypt since 1900 until now, the November 22, 1995 (MW 7.2) Gulf of Aqaba earthquake. The PGA values, for rock site, for Nuweiba are 0.16, 0.29 and 0.38 g, and for Cairo are 0.06, 0.13 and 0.18 g, for return periods of 100, 475 and 975 years, respectively. While, the maximum seismic hazard values for Nuweiba and Cairo are observed at natural period of 0.1 sec, which equal to 0.16, 0.74 g and 0.98 g (for Nuweiba), and equal to 0.15, 0.32 and 0.44 g (for Cairo), for return periods of 100, 475 and 975 years, respectively.