Present-day tectonic stress regime in Egypt and surrounding area based on inversion of earthquake focal mechanisms

Abstract

Stress field inversion is performed in Egypt on the basis of 219 focal mechanism solutions in the period from 1955 to 2007. For this purpose Egypt is divided into six seismotectonic zones: the northern part of the Gulf of Suez, southern Gulf of Suez, and Gulf of Aqaba, Cairo-Suez district, Dahshour zone and the Aswan Zone. The entire Gulf of Suez is currently under extensional stress field, with NE–SW trending horizontal extension. In the Gulf of Aqaba, the strike-slip regime predominates with sub-horizontal σ1 and σ3 axes trending NNW and ENE, respectively. A normal dip slip with small strike-slip component due to a nearly sub-vertical σ1 and sub-horizontal NNE striking σ3 characterizes Cairo-Suez district and Dahshour zone. Aswan seismic zone shows mainly strike-slip stress regime with a slight extension component (horizontal NW σ1 and NNE σ3). The stress field derived in this study indicates a prevailing tension stress (σ3 horizontal) which agrees well with the general tectonic frame of northeastern African, which is subjected to tensional stresses. Generally, extensional and/or extensional-strike slips are dominating the Egyptian territory. These regimes are compatible with the kinematics of the Red Sea–Gulf of Suez rift and Gulf of Aqaba transform plate boundary. Furthermore, the inferred stress in the present study (SHmin directed NNE–SSW) for the Cairo-Suez, Dahshour, and Aswan areas is similar to the East African Rift stress fields “Congo and Sudan” especially (Bosworth et al., 1992; Delvaux and Barth, 2010), whose origin is attributed to the far field effects of ridge push in the Atlantic and Indian Oceans (Zoback, 1992).