Tsunami hazard and risk assessment for Alexandria (Egypt) based on the maximum credible earthquake

Abstract

Throughout its history, the northern coast of Alexandria has experienced devastating earthquakes and tsunamis impacts from tsunamigenic sources in the Eastern Mediterranean. The most hazardous tsunami events for Northern coast of Egypt were related to the earthquakes of 365 in Crete with Mw8.5, 1222 in Cyprus with Mw 7–7.5, and 1303 in Rhodes Island with Mw8.0.The 365 and 1303 earthquakes were accompanied by tsunamis that resulted in widespread destruction and subsequent fatalities along the coast of Alexandria as evidenced by the available historical reports for the Mediterranean region, geomorphologic and paleo-tsunami investigations accomplished recently.In this work, for each tsunamigenic source, i.e., West Hellenic Arc, East Hellenic Arc, and Cyprian Arc, the maximum credible earthquake (MCE) is defined then modeled with NAMI-DANCE. The comparison of the tsunami inundation maps of MCE scenarios computed for each tsunami source shows that the East Hellenic arc (EHA) is the most hazardous source for the Alexandria coast, with a tsunami wave height of 5.5–6.0 m, while the Cyprian arc (CA) is the least hazardous source.The aggregated tsunami inundation map for Alexandria defines the furthest boundary between inundated and non-inundated lands and is associated with hazard levels based on water heights. This map shows that the coasts of Al Amereya district and Borg Al Arab city are expected to be more affected than the others districts. It also indicates that the west side of Alexandria, called Al Sahel Al Shamally, is expected to have less impact than the eastern side, because it is naturally protected by a barrier of carbonate material parallel to the shoreline.The exposure analysis shows that more than 85,000 people are located in the tsunami hazard zone (representing 15.8% of Alexandria governorate's population). Regarding buildings and infrastructure, the most exposed district is Al Amereya with 65.8% of total exposed objects. Among the buildings, the residential ones are the most exposed and about 21% can be classified as highly vulnerable.In terms of risk assessment, the Al Amereya district is identified as the area with the highest tsunami risk.