Asymmetry of faults and stress patterns within the Dead Sea basin as displayed by seismological analysis

Abstract

The Dead Sea pull-apart basin (DSB), which is located within the Dead Sea Transform fault system, displays tectonic asymmetry between its eastern and western longitudinal zones. We investigate the seismological and mechanical signature of this asymmetry by the analyzing the hypocenter distribution and focal-mechanisms of 114 Mw = 1.5–5.2 earthquakes recorded from 1985 till 2012. The analysis indicates that the seismicity along the western longitudinal zone is deeper than the eastern one. Focal mechanism analysis indicates that about 50% of solutions are strike-slip, compatible with the plate motions along the Dead Sea transform. Comparison between the two longitudinal zones of the basin shows that the focal mechanisms in the eastern DSB are dominated by strike-slip faulting shallower than 12 km depth, whereas those in the western DSB are dominated by oblique faulting below 12 km depth. The b value of the Gutenberg-Richter magnitude distributions also show difference between the two zones with ~0.9 in the west and ~0.7 in the east zone.We develop stress-inversion analysis to identify the fault planes of the focal mechanisms by using friction-dependent selection process. The horizontal maximum compression (σHmax) trends NNW-SSE, with increasing value of the vertical stress component along the western part of the basin, corresponds to the oblique faulting in this zone. The optimal friction coefficient determined by the stress-inversion for the fault planes is μ ~ 0.5. Our analysis emphasizes the significant contribution of frictional dependent stress-inversion as an effective tool in seismotectonic analysis.