NEARLY A MILLENNIUM OF SEISMIC QUIESCENCE IN AQABA, JORDAN ALONG THE SOUTHERN DEAD SEA TRANSFORM

The city of Aqaba, Jordan with a population of 70,000 straddles the seismically active Dead Sea Transform plate boundary at the northern shore of the Gulf of Aqaba. Earthquake awareness in Aqaba was significantly heightened after the 1995 Mw 7.3 Nuweiba earthquake when amplification of peak ground acceleration caused local damage. Our analysis of borehole data clearly demonstrates that the sediments along the beach front are susceptible to liquefaction. Furthermore, our paleoseismic data indicate that 800-900 years have lapsed since the last ground-rupturing earthquake. The strike-slip, Aqaba fault emerges from the gulf and appears to cross both the 7th-11th century Islamic walled city of Ayla and the 3rd-6th century Byzantine ruins and terminate under the city. The fault morphology is today totally obscured by urban development within the modern city of Aqaba. The location of the Aqaba fault is constrained to lie east of several distinct, NW-trending cross faults. These cross faults are active and marked by distinct fault scarps. Structurally, the normal to oblique slip on the cross faults indicates active NE-directed extension that produces subsidence at the head of the Gulf of Aqaba. Our paleoearthquake data from trenches excavated across the cross faults indicate repeat motion on the faults with the latest scarp forming around A.D. 1045-1278 (probably in the historical earthquakes of 1212 or 1068). The ancient Islamic walled city of Ayla is known from Arabic historians to have been completely destroyed in the earthquake of March 18, 1068. Archaeological excavations at Ayla revealed walls that were tilted, slumped, and shifted completely off their foundations. Recent excavations of a monumental Byzantine mudbrick structure (perhaps a church) indicate that a portion of this building collapsed in the earthquake of May 19, 363 A.D. This date is derived from over 100 coins of Constantius II (337-361 A.D.) found beneath tumbled mudbrick walls. Subsequent inhabitants repaired wall join separations and fissures in the standing walls. These fissures were later faulted to the surface of the cultural debris and sediments dated to the 7th-8th century. One 4th century wall at the south end of the site appears to be offset by at least two earthquakes. These data indicate primary tectonic faulting in Aqaba in the 4th and 11th century.