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Alexandria , as a second major city of Egypt, becomes nowadays a site for new developmental projects. Therefore, the seismic hazard analysis would be essential to mitigate the earthquake disaster in the region. The seismic hazard maps of different non-exceedence probability for Alexandria are presented. The obtained results indicate that Alexandria is highly affected by earthquakes are generated north of Red Sea and its two branches (Gulf of Suez and Gulf of Aqaba). Recently, the southwest Cairo (Dahshour district) is reported as a source region and poses an effect on the new constructions in Alexandria. Detailed seismic hazard estimation has been carried out for three important constructions: Alexandria Library, Stanley Bridge and the fort of Qaitbay (old Alexandria lighthouse). At the three sites, four intensity levels have been examined. The annual expected number of earthquake, the return period, and the probability of occurrence were calculated for each intensity level. The obtained results indicate that the return period of intensity 5.0 for the Alexandria Library and Stanley Bridge is about 47 years with 2.0% probability of occurrence. Thus, Alexandria Is and area of moderate seismic hazard.
On May 28, 1998, a moderate size earthquake of magnitude 6 occurred at lat, 31.45°N; long. 27.63°E. It was strongly kit in the northern part of Egypt. This study presents its intensity distribution based on the field observations and 280 MMI questionnaires describing the situation in the northern part of Egypt immediately after the mainshock. These reports indicate that this earthquake caused a strong shaking in Cairo and in many localities along the Nile Delta area. Cracks on buildings were observed in several places in Mersa-Matruh province, the western area of the Mediterranean Sea coast in Egypt, but cracks on ground were only observed on the sea beach area of Ras E1-Hekma village. Based on these data, the intensity-distribution map is presented here; its isoseismals are of non uniform distribution. The attenuation of MM intensity (I) with epicentral distance (D in km) of the studied shock is determined using a simple relation of type log I = log Io - mD, where Io is the epicentral intensity and m is constant. According to the variation in m constant, the isoseismal map of the studied area is divided into two zones, (a) and (b) of which zone-a is characterized by a higher m. The interpretation of the remarkable change in the m-value is attributed to the obvious variations in geological structures between zone-a and zone-b.
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