Active faulting in the Gulf of Aqaba: New knowledge from the M-W 7.3 earthquake of 22 November 1995

On 22 November 1995 the largest earthquake instrumentally recorded in the a rea, with magnitude M-w 7.3, occurred in the Gulf of Aqaba. The main ruptur e corresponding to the strike-slip mechanism is located within the gulf of Aqaba, which forms the marine extension of the Levantine fault, also known as the Dead Sea fault. The Levantine fault accommodates the strike-slip mov ement between the African plate and the Arabian plate. The Gulf of Aqaba it self is usually described as the succession of three deep pull-apart basins , elongated in the N-S direction. Concerning historical seismicity, only tw o large events have been reported for the last 2000 years, but they are sti ll poorly constrained. The seismicity recorded since installation of region al networks in the early 1980s had been characterized by a low background l evel punctuated by brief swarmlike activity a few months in duration. Three swarms have already been documented in the Gulf of Aqaba in 1983, 1990, an d 1993, with magnitudes reaching at most 6.1 (M-w). We suggest that the geo metry of the rupture for the 1995 event is related to the spatial distribut ion of these previous swarms. Body-wave modeling of broadband seismograms f rom the global network, along with the analysis of the aftershock distribut ion, allow us to propose a well-constrained model for the rupture process. Northward propagation of the rupture has been found. We have demonstrated t hat three successive subevents are necessary to obtain a good fit between o bserved and synthetic wave forms. The total seismic moment released was 7.4 2 x 10(19) N-m. The location of the subevents shows that the three stages o f the rupture involve three different segments within the gulf. Substantial surface breakage showing only normal motion (up to 20 cm) affecting beachr ock was observed along the Egyptian coast. We show that these ruptures are only a secondary feature and are in no case primary ruptures. The stress te nsor derived from striations collected in quaternary sediments shows radial extension. This result supports landsliding of the beach terraces under th e action of the earthquake shaking.