STUDY OF SEISMIC ACTIVITY AND ITS HAZARD IN SOUTHERN EGYPT

Abstract

Before installation Aswan seismic network, a few number of large earthquakes occurred in Red Sea and one in Gulf El-Kebir had been reported in the upper Egypt in the Catalog of the International Seismological Center, because the closest station to record earthquakes in upper Egypt was Helwan station, it is not possible to locate the small magnitude earthquakes in upper Egypt. The first seismograph installed in upper Egypt that was capable of recording small local earthquakes were the Soviet short-period (SMK) instruments installed at Aswan and Abu-Simbel in 1975. On June 1982 a telemetry seismic network installed around the northern part of the High Dam Lake and another station was installed in 1990 ip Marsa Alam town along the Red Sea coast to observe and detect the seismic activities at Abu-Dabbab area and the Red Sea. The earthquakes, which occurred in upper Egypt and observed by many

seismic stations, are located and plotted on a geographic map of all studied regions, new seismicity map for the southern part of Egypt was designed. According to the spatial distribution of earthquakes located m the studied

areas, seven areas having different seismicity level have represented in southern part of Egypt and known as Shadwan Island, the Red Sea, Abu Dabbab, the Eastern Desert, Aswan, Abu-Simbel and the Western Desert area. A seismicity map was conducted for every active zone in upper Egypt, the relationship between the geologic structure and earthquakes was studied in every investigated area. The frequency­ magnitude relationship for the data located in each area was plotted and exhibits a good fit to a line. The focal mechanism solution of the significant earthquakes in each active area was evaluated by using the polarity of first arrival techniques. Using the seismicity map of upper Egypt and its vicinity during the period from 1900 to 2001 the probabilistic seismic hazard analysis was conducted in detail. The objective was to evaluate the probability of exceedance for different levels of ground shaking due to earthquakes, which occurred in the studied areas and vicinity during the period from 1900 to 2001. The probability approach was used to assess the seismic hazard of the studied area using area source model. The probabilistic