Tectonic evolution and seismic hazard analysis of the Damour-Beit ed Dine fault system -

Abstract

Tectonic deformation accommodated by rotating parallel faults is known as bookshelf faulting. Several examples from around the world show that it is an efficient mechanism in accommodating part of the strain generated from shearing on overlapping parallel transform faults. The Mt. Lebanon Range is dissected by several E-W faults, most likely activated as counter-clockwise (CCW) dextral bookshelf structures during the Cenozoic. Yet their kinematic evolution seems more complex due to the presence of an older, Mesozoic, normal component on many of these structures. Here we show that the 25Km long Damour-Beit ed Dine Fault, the southernmost of the E-W old Mesozoic normal faults in Lebanon, reactivated most-likely as a CCW, dextral bookshelf structure during the Cenozoic which translates into seismic hazard for the surrounding area. We also show that the Southern Central Mt. Lebanon (SCML) is characterized by WSW-ENE shortening responsible for the uplift of this area in the Cenozoic. Using morphotectonics and seismicity analysis we prove that the DBF is an active structure. The drainage pattern in the area readjusted to the active growth of the structures leaving wind gaps. Structural mapping show ~2Km of cumulative dextral displacement associated with the Late Miocene-present CCW bookshelf reactivation of the DBF, induced by the sinistral shear on the Lebanese Restraining Bend. The smaller scale NW-SE faults mapped north of the DBF, have similar Mesozoic-Cenozoic evolution. Their reactivation in the Cenozoic as CW, sinistral bookshelf faults resulted in their 10°-18° CW rotation relative to similar structures south of DBF. We also measured at least 3percent shortening in a 22Km distance along an E-W direction in the SCML. We suggest that folding in the SCML is also compatible with overall shortening and thrusting in Lebanon. Also, we compiled instrumental and historical seismicity catalogs of the area, converted to a uniform coda magnitude scale. We assessed the accuracy of earthquakes’ location for the