Crustal structure of the Dead Sea Basin from local earthquake tomography

Abstract

New findings of the velocity structure of the crust across the Dead Sea Basin are obtained by applying tomography-based method to local earthquakes. We use P-wave traveltime of 614 earthquakes that occurred in the Dead Sea Basin in 1983-2009. At all depths, the Dead Sea Basin is characterized by lower velocities relative to both the eastern and western sides of the basin. There is significant seismic activity at a depth of about 20 km, mainly in the centre and the northern part of the basin. At shallow depths (<15 km) there is more seismic activity on the eastern side of the basin than on the western side, and the northern basin is generally more active than the southern basin. Asymmetry is also observed in the faults that border the Dead Sea Basin. The Arava Fault on the eastern side, with nearly vertical dip faulting, appears to be a clear boundary at all depths down to about 20 km. The depth extension of the Jericho Fault on the western side of the basin is definitely limited to less than 15 km. At greater depths of 20 km or more, the western side is only partially bounded by a fault. The concentration of earthquakes in the central part of the basin at depths larger than 15 km suggests that the Dead Sea Fault at those depths acts as one single fault that is located in, or near, the central axis of the basin. The existence of a number of clusters of earthquakes that spread from shallow depths of a few kilometres up to a depth of about 22 km, points to several defined faults that traverse the Dead Sea Basin. One such example is the aftershock sequence of the 2004 earthquake that occurred in the northern Dead Sea Basin. Seismic activity near Mt Sodom is relatively low and occurs at shallow depths down to 10 km, whereas at larger depths (≥ 15 km) it ceases. This implies that the whole structure is relatively shallow with no wide and deeper extension. Seismic activity near and within the Lisan Peninsula extends to somewhat larger depths (~15 km), and then it ceases. The occurrence of earthquakes at large depths suggests that the upper and the lower crust are relatively cool, as was also suggested by earlier studies, pointing to the fact that the heat flow is significantly below the global average value.