GPS measurements of present-day crustal deformation within the restraining bend of the Dead Sea fault system in Lebanon

Abstract

Lebanon and southwestern Syria comprise a prominent, 200-km long restraining bend along the Dead Sea fault system (DSFS) - the continental transform boundary between the Arabian and Sinai plates. Within this "Lebanese Restraining Bend", the DSFS splays into several prominent, left-lateral strike-slip faults, in addition to uplift owing to regional transpression. Hence, upper crustal deformation resulting from the relative motion between the Arabian and Sinai plates is likely distributed among multiple geological structures. We present new Global Positioning System (GPS) measurements that help constrain relative plate motion along this portion of the plate boundary and explore strain partitioning of the plate motion within the restraining bend. Our GPS observations were collected during 5 survey campaigns in Lebanon spanning more than 3 1/2 years. The regional survey network consists of 14 survey sites, along with one continuous GPS station (LAUG in Jbail, Lebanon). Our measurements are processed along with other continuous stations in the region and stabilized using the global ITRF2000 reference frame core sites. For tectonic interpretation we rotate this solution into the Arabian, Nubian and Sinai fixed plate reference frames. Across the restraining bend, we constrain the 4 - 6 mm/yr of plate motion, with 1-sigma uncertainties typically less than 1 mm/yr. The plate motion is particularly well constrained between the continuous GPS stations in Jbail and Damascus (Syria). Within the uncertainties, GPS-based velocities compare well with Holocene-averaged estimates of slip along the Yammouneh and Serghaya faults. Furthermore, displacement gradients also suggest small, but measurable, horizontal shortening across the Mt. Lebanon range. We develop our kinematic model further by applying an elastic block model to assess the kinematics of the restraining bend and constrain geodetic locking depths. These results provide critical constraints for documenting and assessing the earthquake hazard in Lebanon and nearby regions of Syria.