The active structure of the Dead Sea Depression

Abstract

The Dead Sea Depression is an ∼230-km-long and up to ∼10-km-deep structural-gravitational low along the southern Dead Sea Transform plate boundary between Africa and Arabia. Following an early Miocene–Pliocene deformation phase of localized strike slip faulting and intense fluvial deposition in confined pull-apart basins, delocalization of the Dead Sea Transform and formation of a shear zone over the entire current width of the Dead Sea Depression took place in late Pliocene–early Pleistocene time. Integration of relocated epicenters and focal mechanisms of ML 2.5 earthquakes with a range of structural and geophysical data shows that the late-phase asymmetrical shear zone consists of a distinct sinistral boundary fault in the east and a broad zone of distributed shear to the west. It is characterized by a penetrative, bimodal (NW and NE) structural orientation pattern reflected in earthquake focal mechanisms, segments of the western boundary fault system, fracture sets, geomorphic lineaments, and linear clusters of collapse sinkholes. These phenomena are a manifestation of a long-term persistent deformation field that involves at least the entire upper crust. The shear zone fault structure consists of normal-dextral, NE-oriented faults that extend northeastward from the western boundary fault and intervening NW-trending normal faults. These fault sets produce subsided, fault-bounded depocenters within the Dead Sea basin. The NE-oriented and axially extending blocks are expected to rotate in a clockwise sense with the relative sinistral plate motion, resulting in both normal-dextral and normal-sinistral slip events along the western boundary fault system. Since the Dead Sea Transform plate boundary is non-convergent and probably driven by sinistral basal flow, the Dead Sea Depression shear zone is internally contracting and subsiding. Partition of the relative plate motion between sinistral slip along the eastern boundary fault and distributed shear within the Dead Sea Depression may explain the apparent deficiency in seismic slip along the southern Dead Sea Transform relative to average long-term geological slip.