Structure and Dynamics of the Dead Sea Transform in the Middle East

Despite numerous efforts to study large transform systems, especially at the San Andreas Fault (SAF) system, the processes responsible for large continental-scale shear zones, one of the key elements of plate tectonics, and their relation and interaction with the crust and upper mantle are still not fully understood. The Dead Sea Transform (DST), at the border between Israel and Jordan, has for a long time been considered a prime site to examine large shear zones, but due to the political situation in this area no geoscientific profile has crossed the DST. Moreover, studies of historical earthquakes of the past few thousand years, paleoseismic studies and instrumental earthquake studies demonstrate that a number of damaging earthquakes have occurred along the DST. The DST therefore poses a considerable seismic hazard to Israel, Jordan, and the Palestine Authority. A geophysical profile crossing the DST, the boundary between the African and Arabian plates in the Middle East, and the border between Israel and Jordan, has been completed for the first time. High-resolution seismic tomography and magnetotelluric sounding of the shallow crust show drastic lateral changes in material properties within a narrow zone around the DST. The seismic basement is offset by 3-5 km under the DST, and strong lower-crustal reflectors are imaged east of the DST. The seismic velocity sections show a steady increase in the depth of the crust-mantle transition (Moho) from 26 km at the Mediterranean to 38-39 km under the Jordan highlands, but only small topography of the Moho under the DST. These observations can be linked to the left-lateral movement of the two plates of 105 km in the last 17 Ma accompanied by strong deformation within a 20-30 km wide zone cutting through the entire crust. Sub-horizontal lower-crustal reflectors and deep reaching deformation zones occur in the DST (originating in a relatively homogeneous cold and stable lithosphere; slow relative plate motion of ca 0.5 cm) and also in the San Andreas Fault system (originating in a strongly heterogeneous, hot lithosphere; fast relative plate motion of ca. 3.5 cm). The fact that lower-crustal reflectors and deep deformation zones are observed in transform systems of such different origin could suggest that these structures are fundamental features of large transform plate boundaries.