The Gulf of Aqaba earthquake swarm of 1983 January-April

Abstract

than 500 local earthquakes (ML Q 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 t o 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 foreshockaftershock 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. IntroductionAn earthquake swarm occured in the Gulf of Aqaba area (Fig. l), in the period 1983 January 21 to April 20, during which 60 shocks (1.7 Q M L Q 4.85) were recorded on the Jordan University Seismological Station, some 350 km distant. With no distinctive main shock, the level of activity fluctuated with time, reaching its highest on February 3 when a few large shocks (including the largest of the swarm) occurred and were widely felt in the Saudi town of Haql, Aqaba and the surrounding region, thus causing panic and concern. On February 8, a temporary seismic station was installed near Haql. Within its 72 days of operation, more than 500 shocks (0.0 G M L G 3.5) were recorded, showing a decreasing level of activity with time. By April 20, the level of seismicity in the Gulf seemed to have returned to normal.

Seismotectonic regionalization of the Red Sea area and its application to seismic risk analysis

“…The anticlockwise separation of the Arabian peninsula started during the process of rifting of the Red Sea and of the Gulf of Suez (Oligocene to earliest Miocene), went on through the formation of the Gulf of Aqaba graben and the Wadi Araba (El-Isa et al, 1984;Mechie and El-Isa, 1988) or Arava (Lyberis, 1988) transform fault (Middle Miocene), and continues to the present days.…”

زلزالية شبه جزيرة سيناء - مصر

“…Both swarms characterize the Jordan-Dead Sea transform and with mainshock-aftershocks types of earthquake activity. El-Isa et al (1984) attributed the swarm phenomenon to the subsurface magmatic activities and/or to the isostatic adjustments in the Gulf of Aqaba. The leftlateral distortion and dislocation of walls of an eighth century palace located west of the main trace of the Jordan fault (Reches and Hoexter 1981) indicate that not all the shear strain is accommodated along the main trace of the Jordan fault, but also some is distributed throughout a border area of the Jordan valley.…”

“…In 1972, an earthquake swarm occurred at the southern entrance of the Gulf of Suez. The 1983 Gulf of Aqaba earthquake swarm (El-Isa et al 1984;Merghalani and Bazari 1984;Shapira and Jarradat 1995) caused panic damages within and around the Gulf of Aqaba cities. An earthquake swarm occurred from August 1993 up to February 1994 south of the 1983 swarm.…”

Structural and Geotechnical Aspects of the 1995 Gulf of Aqaba Earthquake

“…Between January 21 and April 20, 1983, more than 500 earthquakes with local wave magnitude of M L = 4.8 or smaller occurred in the Gulf of Aqaba area 6) . The strongest shocks were felt in towns on the Gulf and caused widespread concern.…”