Seismic hazard maps of Egypt based on spatially smoothed seismicity model and recent seismotectonic models

Abstract

An earthquake catalogue of Egypt is a vital element for seismotectonic and seismic hazard studies using different approaches. Therefore, an updated earthquake catalogue for Egypt and its circumference is collected. The collected earthquake catalogue includes the historical and the instrumental seismic records. Data sets of all earthquakes with a magnitude (M), M ≥ 3, on any magnitude scale mentioned in local, regional, and international sources are included. The collected catalogue contains 5894 earthquakes. Contaminated events, low reliability, and duplicate events are identified using the available current knowledge and then have been removed. Special priorities were considered through the removing process. The processed catalogue contains 4776 earthquakes. We searched for the moment magnitude (Mw) of each earthquake in the original data sources and publications. When Mw is not available, the moment magnitude is calculated through empirical relationships which are obtained in the current study using the orthogonal regression method. The catalogue is de-clustered aiming to eliminate the dependent events using three de-clustering techniques. Completeness test of the entire catalogue is performed. Based on the processed catalogue, the spatial diversity of the Egyptian seismic activity is represented for the first time. The a-value, b-value, and the maximum estimated magnitude of the recently delineated Egyptian seismic source zones are calculated. Probabilistic seismic hazard assessment (PSHA) is calculated using two recently delineated seismotectonic models, two different smoothed seismicity maps and three ground motion prediction equations (GMPEs). Different seismotectonic models and GMPEs are put into the logic-tree practice for treating the epistemic uncertainties accompanying the hazard calculations. The produced seismic hazard maps represent the peak ground acceleration (PGA) and the spectral acceleration (SA) corresponding to 0.2 and 1 s (s) natural vibration periods for 475 and 2475 years return periods (RPs). The produced hazard maps illustrate that the Gulf of Aqaba area is exposed to the highest acceleration, while the Western Desert is exposed to the lowest ones. For instance, the map of PGA for 475 years RP shows PGA values of 0.229 g close to the Gulf of Aqaba and 0.005 g at the Western Desert.