FOCAL MECHANISM ANALYSIS OF THE 1988, 1993, 1994, 1995, AND 1996 SOUTHERN RED SEA EARTHQUAKE SEQUENCES

Since 1967 to 1996, seven earthquake sequences have occurred along the southern Red Sea region, even though in general the seismicity has been described as moderate. Focal mechanism solutions were obtained for twenty seven earthquakes derived from previous and recent southern Red Sea swarms. The earthquakes are clustered along the segments of the axial trough and are located in two regions, (I) latitudes 19.5N and (II) 16.6N, respectively. The fault mechanisms show two styles: region (I) normal faulting with a few events showing strike-slip components, while region (II) is characterized by left-lateral strike-slip motions. The general trend of the T-axes for region (I) conforms with the NE movement of the Arabia plate, while the T-axes of region (II) are oblique to it. These contrasted styles of faulting indicate two different tectonic regimes. Region (I) lies in the Rift Valley and region (II) lies in the proposed Southern Transitional region. The Rift Valley region attains the most advanced stage of evolution that is manifested by organized spreading and existence of true transform faults. The Southern Transitional region is characterized by strike-slip processes and unorganized spreading that indicates its transitional nature.