The Gulf of Aqaba earthquake swarm of 1983 January-April

Abstract

Summary. In the period 1983 January 21 -April 20, more than 500 local earthquakes (ML≤ 4.85) occurred in the Gulf of Aqaba area between latitudes 29°00′and 29°25′and longitudes 34°30′and 34°45′. Most of the activity including the largest shocks was restricted to the area between latitudes 29°07′and 29° 15′and longitudes 34°33′and 34°42′where the NW Atiya regional dyke crosses the area and is horizontally displaced by NE strike-slip faults. The first-motion directions of four large shocks, including the largest, at both UNJ and HLW stations are in agreement with a strike-slip mechanism at a NE-trending fault in this area. The b value showed a temporal increase with time from 0.43 to 0.69. This, together with other geological and geophysical observations may indicate that subsurface magmatic activity has affected the stressed crustal rocks, thus triggering earthquake activity. This swarm and historical information indicate that the Gulf of Aqaba-Dead Sea Jordan transform is characterized by both swarm and foreshock-aftershock types of seismic activity and therefore the relatively large proportion of non-seismic slip along the southern part of this transform may actually be higher if swarm-type activities are considered.