Mechanical contrast and asymmetric distribution of crustal deformation across plate boundaries: Insights from the northern Dead Sea fault system

The distribution of permanent deformation near strike-slip plate boundaries and the underlying controlling variables are commonly poorly understood. Here we examine the crustal deformation across the northern Dead Sea fault system based on paleomagnetic observations and mechanical modeling. We focus our investigation on the region of the Lebanese restraining bend where the fault system strikes obliquely to the general Sinai-Arabia plate motion. We construct a series of crustal elasto-plastic models in which kinematics is based on geodetic measurements, and the geometry of the plate boundary is constrained by gravity data. Both the observed regional vertical axis rotations and the model results display significant counterclockwise rotations (as much as ~50°) confined to the northern Sinai microplate located west of the bend. On the other hand, relatively minor rotations (<~10°) are displayed for the adjacent Arabian plate. Our results, validated by structural evidence, suggest that the northern Sinai microplate is mechanically weaker than the adjacent crust of the Arabian plate. This mechanical contrast, along with the oblique convergence and change of slip rate along the Dead Sea fault system, is required to simulate the observed rotations. We propose that the crustal mechanical contrast across plate boundaries is a key parameter responsible for the distribution pattern of permanent vertical axis rotations.