Preliminary seismicity and focal mechanisms in the southern Gulf of Suez: August 1994 through December 1997

摘要

This paper shows an evaluation of the seismic activity in the entrance of the Gulf of Suez using the data recorded by Hurghada Seis-mological Network (HSN), in the period between August 1994 and December 1997 and represents an extension for the work published by the previous investigators. Hypocentral locations were determined for 180 earthquakes (duration magnitude ranged between 1.6 and 4.3) selected from 300 recorded events. All these events are located with epicentral error and depth error of less than 2 km. The spatial distribution of these earthquakes indicates the presence of three active areas. These are Shadwan Island, Gubal Island and the area adjacent to the southern tip of Sinai Peninsula. Such pattern of activity implies a localization of stress below these areas. The concentration of the stress field in these areas may have been strongly controlled by ductile necking and or intrusion. Composite fault plane solutions were also constructed for each of the three active areas. The data for each area was divided into groups, according to geographical position and uniformity of polarity data. In Shadwan Island, the composite fault plane solution of 15 events shows almost pure dip-slip motion. The composite fault plane solutions in Gubal Island and the area adjacent to the southern tip of Sinai Peninsula indicate a mixed regime of both strike-slip and extensional faulting mechanisms. The stress regime obtained from the fault plane solutions in this study is predominantly NNE-SSW tensional stress field. This result is consistent with the present day stress field, which has a 010° ± 18° orientation. The overall results are correlated with the structural setting of the area known from other sources.