A non-active fault within an active restraining bend: The case of the Hasbaya fault, Lebanon

Abstract

The Hasbaya fault is a 50-km-long fault branch of the Dead Sea Transform Fault within the Lebanese Restraining Bend. It lies within the intersection zone of Mount Lebanon and Anti-Lebanon chains, along the western flank of Mount Hermon. It is little studied, its tectonic behavior is unknown, and its role among the other active fault branches of the restraining bend is the least defined. It was mapped as a discontinuous array of fault segments, with minor displacements and tectonically undisturbed basaltic cover. We studied the Hasbaya fault with detailed field mapping, and combining geomorphology, structural geology, and active tectonic investigations. The results reveal little and localized faulting along the entire length of the fault, with no signs of tectonic correlation between the drainage network evolution and the tectonic activity of the fault. The absence of active-tectonic surface features along the Hasbaya fault trend indicates that it does not manifest enough surface evidence to be classified as a tectonically active structure within the Lebanese Restraining Bend, and subsequently does not appear to be a major source of seismic hazard in the region. It may be related to the subsurface structure that controls the monocline that forms the western flank of Mount Hermon, or it may represent the remnant of an old suture zone between Mount Lebanon and Anti-Lebanon as a part of the regional compression imposed across the restraining bend. Our results shed light on the role of the non-active Hasbaya fault in a zone of active faults within a restraining bend, which may provide a case with broader implications on comparable tectonic settings worldwide.