New GPS observations on fault slip rate and locking depth for the northern Dead Sea Fault System in western Syria: Implications for tectonics and earthquake hazards

The Dead Sea fault system (DSFS) is the transform plate boundary between the Arabian and Sinai plates in the eastern Mediterranean region. Along part of the northern DSFS in northwestern Syria, paleoseismic and historical studies document repeated large earthquakes over the past 2000 years, although the region has not experienced a large (magnitude > 7) earthquake in more than 800 years. We present new Global Positioning System (GPS) measurements that provide the first direct observations of near-field deformation associated with the DSFS in northwestern Syria. A network of 34 stations, including a closely spaced profile across the fault, was surveyed in 2000 and 2007. Preliminary velocities demonstrate left-lateral shear with 1-sigma uncertainties less than 1 mm/yr. These velocities are consistent with an elastic dislocation model involving a slip rate of 1.4 - 2.0 mm/yr and a locking depth of 10 - 22 km. This geodetically determined slip rate is less than that reported farther south along the central section (Lebanese restraining bend) and southern section (Dead Sea and Wadi Araba) of the transform and consequently requires some deformation to occur away from the transform. One possibility may be north-south shortening within the southwestern segment of the Palmyride fold belt of central Syria. This difference in slip rates along the transform is also consistent with differing estimates of total fault slip that have occurred since the mid Miocene: 20 - 25 km along the northern DSFS versus about 45 km along the southern DSFS. These new GPS measurements, when viewed alongside the paleoseismic record and the modest level of present-day seismicity, suggest that the reported recurrence rate of large earthquakes along the northern section of the DSFS may be overestimated owing to temporal clustering of large historical earthquakes. Hence, a revised estimate of the earthquake hazard may be needed.