Updated Probabilistic Seismic‐Hazard Values for Egypt

Abstract

Seismic hazard in terms of mean peak ground acceleration (PGA) and spectral acceleration (SA) values has been computed for Egypt using both historical and instrumental earthquake data. For this purpose, an updated earthquake catalog, spanning the time period from 2200 B.C. to 2013, has been compiled for Egypt as well as its surrounding regions and is prepared to be used in a new probabilistic seismic‐hazard assessment of Egypt. The earthquakes sizes were unified in terms of the moment magnitude scale. A new seismic source model for the seismic activity in and around Egypt, consisting of a total of 88 seismic zones (for shallow‐ and intermediate‐depth seismicity), was considered in this new assessment. The seismicity parameters have been specifically computed for 35 seismic sources covering the Egyptian territory and the Eastern Mediterranean region. A logic‐tree design was set up to consider the epistemic uncertainty in the Gutenberg–Richter b ‐value, maximum possible magnitude ( M max), and the selected ground‐motion prediction equations. Seismic‐hazard computations for rock‐site conditions with 10% and 5% probability of exceedance in 50 years were carried out. In addition, uniform hazard spectra for twelve, among the most important and populated cities in Egypt, are computed and compared with the most recent Egyptian building code values. It is interesting to highlight that the maximum hazard values are observed at the Gulf of Aqaba region, specifically around the epicentral location of the biggest Egyptian recorded earthquake of 22 November 1995 ( M w 7.2) Aqaba earthquake. The obtained seismic‐hazard values for Nuweiba city (located in this region) for mean PGA and SA (0.1 s) are 0.29 g and 0.74 g , respectively, for a return period of 475 years.