PALEOSEISMIC TRENCHING ALONG THE DEAD SEA TRANSFORM IN THE TABA SABKHA IN WADI ‘ARABAH, JORDAN

The Taba sabkha is a continental sabkha located in the Wadi ‘Arabah valley approximately 35 km north of the Gulf of Aqaba in Jordan. The sabkha, an area of approximately 55 km², forms the distal facies of several alluvial fans emerging from the basement rocks that surround the valley, and is a part of the larger Timna basin that developed along the active Dead Sea transform (DST) fault. The DST is a left-lateral transform boundary separating the Arabian and African plates, and is composed of a series of strike-slip fault basins arranged en-echelon. The Taba sabkha receives a nearly constant supply of sediment from discharge from short ephemeral streams (wadis) draining the nearby mountains and adjacent upland plateau, has almost no topographic expression, save for a small pressure ridge outlining the DST fault trace, and thus provides ideal conditions for preserving the evidence of ancient earthquakes by rapid burial. We excavated a 15 x 4 m paleoseismic trench to a depth of 2.5 m in the Taba sabkha at a site located west of the Dead Sea highway as a part of the Wadi ‘Arabah Earthquake Project to determine the number and frequency of earthquake events occurring along this southern DST fault segment. Analysis of the trench stratigraphy, which is dominated by sand, silt, and clay, shows evidence for at least three separate faulting events, with the most recent event located at a depth of 50 cm below the ground surface. These findings support the initial ground penetrating radar survey conducted at the southern end of the Taba sabkha by Abueladas (2005). Four radiocarbon dates indicate subsidence of the eastern side of the trench due to down-faulting. A radiocarbon date of 280 +/- 20 yr BP was collected from channel sediment that clearly scours the past two seismic events. However, a date of 1055 +/- 40 yr BP was collected from sediment deposited just below this erosional surface toward the center of the trench. At least two earthquakes occurred after a layer dated to 1535 +/- 25 yr BP, suggesting a shorter earthquake recurrence rate that contradicts previous estimations of up to a 1000 year repeat time for major earthquakes. These data, therefore, help to roughly constrain the two most recent seismic events, and also highlight the elevated earthquake hazard potential of the region along the southern Dead Sea transform.