Uplift and subsidence at the periphery of the Lebanese Restraining Bend, Northern Dead Sea Fault

Abstract

Bends and stepovers in strike-slip fault systems along active plate boundaries are widespread and introduce stress heterogeneities, affecting the regional strain field. The strain field associated with these complex fault structures has been extensively studied. Asymmetric uplift of the Lebanon Mountains, located at the fringe of an active plate boundary, the Dead Sea Fault system (DSF), together with subsidence of the Lower Galilee in northern Israel provides an exceptional example of the complex deformational pattern associated with a restraining bend. The deformation field with respect to the restraining bend is expressed by the asymmetric uplift of the Lebanon Mountains, west of the DSF. This asymmetry along with the subsidence of the Lower Galilee, an extensional region in northern Israel, could not be explained only by the impact of the restraining bend, ignoring additional regional tectonic features. We present the results of 3-D numerical modeling of the distributed deformation, utilizing damage rheology for brittle rock deformation of the seismogenic crust overlaying viscoelastic mantle. We use available geological and regional seismicity data to implement the realistic lithosphere structure and to delineate the major faults in the model as localized weak zones. The modeling results highlight the impact of several factors on the spatial distribution of crustal deformation, demonstrated by running different model scenarios. These scenarios allow us to isolate the impact of each tectonic element and show the strain pattern resulting from their superposition, starting with a restraining bend acting in a homogeneous layered crust. Our modeling results suggest that the extension observed in the Lower Galilee region and the asymmetric uplifted pattern west of the Lebanese Restraining Bend is the outcome of three interacting factors, which are the sinistral strike-slip motion along the Lebanese Restraining Bend, the significant variations in the crustal structure (depth to Moho), and the slow extension of the Irbid-Azraq rift zone.