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 seismichazard 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. Seismichazard 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 0:29g and 0:74g, respectively, for a return period of 475 years.

Probabilistic seismic hazard model for Cairo, Egypt: estimates and uncertainties

“…Dahshour and Cairo Suez district sources are treated as a single area source in contrast to previous studies (e.g. Adly 2010;Mohamed et al 2012;Ezzelarab et al 2016;Sawires et al 2016). This is done because they both hosted some foreshocks and aftershocks of the 12th Oct. 1992 earthquake.…”

“…Recently, more detailed seismic hazard studies were carried out (e.g. Deif et al 2011;Mohamed et al 2012;Ezzelarab et al 2016;Sawires et al 2016). However, these studies were based on just area source model interpretation of seismicity and referenced the hazard based on hypothetical common rock site conditions.…”

Identifying Potential Earthquake Sources in Continental Environments

“…Most of the newly released SHA studies for Egypt (e.g., Mohamed et al 2012;Sawires et al 2016b) characterize the seismic hazard in terms of peak ground acceleration (PGA) of horizontal component, which is defined to be poorly correlated with damage, and response spectrum (RS) at different periods rather than the other relevant parameters (e.g., frequency content, effective acceleration). One of the basic problems in the SHA studies is how much the earthquake catalog reflects the real seismic potential of the considered area.…”

Insight on seismic hazard studies for Egypt

“…About 80% of all SHA studies conducted until now about Egypt at different geographic scales are based on the traditional PSHA and despite of the presence of theoretical and practical limitations and poor performance of these approaches, as demonstrated by Panza et al (2014) and references therein, it is still in use in the construction of newly developed SHA maps at different scales (e.g. EzzElarab et al, 2016;Sawires et al, 2016b) upon which the current Egyptian Building Code is dangerously based. The different studies adopting the traditional PSHA method contribute to the development of the collection and revision of input data rather than to the critical revision and improvement of the methodology, elements that are crucially necessary to reach a reliable, as much as possible, estimate of hazard (Tables 1-3).…”