Approximately 4 yr of campaign and continuous Global Positioning System (GPS) measurements across the Dead Sea fault system (DSFS) in Lebanon provide direct measurements of interseismic strain accumulation along a 200-km-long restraining bend in this continental transform fault. Late Cenozoic transpression within this restraining bend has maintained more than 3000 m of topography in the Mount Lebanon and Anti-Lebanon ranges. The GPS velocity field indicates 4-5 mm yr(-1) of relative plate motion is transferred through the restraining bend to the northern continuation of the DSFS in northwestern Syria. Near-field GPS velocities are generally parallel to the major, left-lateral strike-slip faults, suggesting that much of the expected convergence across the restraining bend is likely accommodated by different structures beyond the aperture of the GPS network (e.g. offshore Lebanon and, possibly, the Palmyride fold belt in SW Syria). Hence, these geodetic results suggest a partitioning of crustal deformation involving strike-slip displacements in the interior of the restraining bend, and crustal shortening in the outer part of the restraining bend. Within the uncertainties, the GPS-based rates of fault slip compare well with Holocene-averaged estimates of slip along the two principal strike-slip faults: the Yammouneh and Serghaya faults. Of these two faults, more slip occurs on the Yammouneh fault, which constitutes the primary plate boundary structure between the Arabia and Sinai plates. Hence, the Yammouneh fault is the structural linkage that transfers slip to the northern part of the transform in northwestern Syria. From the perspective of the regional earthquake hazard, the Yammouneh fault is presently locked and accumulating interseismic strain

Evidence of long-term, late Cenozoic uplift, as well as strike-slip faulting, is revealed by topographic and geological features along the northern 500 km of the Dead Sea fault system

Recent neotectonic, palaeoseismic and GPS results along the central Dead Sea fault system elucidate the spatial distribution of crustal deformation within a large (c.180-km-long) restraining bend along this major continental transform. Within the ‘Lebanese’ restraining bend, the Dead Sea fault system splays into several key branches, and we suggest herein that active deformation is partitioned between NNE–SSW strike-slip faults and WNW–ESE crustal shortening. When plate motion is resolved into strike-slip parallel to the two prominent NNE–SSW strike-slip faults (the Yammouneh and Serghaya faults) and orthogonal motion, their slip rates are sufficient to account for all expected strike-slip motion. Shortening of the Mount Lebanon Range is inferred from the geometry and kinematics of the Roum Fault, as well as preliminary quantification of coastal uplift. The results do not account for all expected crustal shortening, suggesting that some contraction is probably accommodated in the Anti-Lebanon Range. It also seems unlikely that the present kinematic configuration characterizes the entire Cenozoic history of the restraining bend. Present-day strain partitioning contrasts with published observations on finite deformation in Lebanon, demonstrating distributed shear and vertical-axis block rotations. Furthermore, the present-day proportions of strike-slip displacement and crustal shortening are inconsistent with the total strike-slip offset and the lack of a significantly thickened crust. This suggests that the present rate of crustal shortening has not persisted for the longer life of the transform. Hence, we suggest that the Lebanese restraining bend evolved in a polyphase manner, involving an earlier episode of wrench-faulting and block rotation, followed by a later period of strain partitioning.

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S U M M A R YThe left-lateral Yammouneh fault (YF) is the main active branch of the Dead Sea Transform Fault (DSTF) within the Lebanese restraining bend. Despite the overall transpressional setting, a series of sedimentary basins have developed along the trace of the YF. Consequently, palaeoseismic studies within these basins provide an opportunity to study the processes of coseismic growth of the basins, as well as elucidate earthquake behaviour of the fault, in general. Geodetic measurements of contemporary fault slip within the Lebanese restraining bend indicate that the YF accommodates most of the expected left-lateral strike-slip motion, despite the apparent lack of present-day seismicity. We studied the YF, using combined investigations of remote imagery, geomorphology and palaeoseismology. The active fault trace along a 51 km strip was delineated as relatively young surface ruptures and fault scarps that affect Holocene deposits with intermittent offset geomorphic markers. Seven closed basins that occur along-strike of the YF, were found to be related to faulting, with at least three of them displaying evident pull-apart settings. We concentrated our work on the rhombohedral Yammouneh basin, an actively evolving example of pull-apart basins, which is presently obliquely cut by the active fault, with an apparently young age of 1.4 ± 0.3 Myr. 3-D correlation and analysis of palaeoseismic investigations exposed a composite shear zone with a total subsidence that exceeds 1.6 m over the past 4000-4400 yr. Stratigraphic and geochronological constraints suggest the occurrences of at least five large faulting events during that period. By correlating the stratigraphy and ages of this trench with a previously published study located nearby, a combined palaeoseismic history for the past five events is constructed. This suggests a mean recurrence period of 1020-1175 yr for large earthquakes along this section of the YF. Our results suggest a subsidence rate due to faulting of about 0.36-0.40 mm yr −1 within the Yammouneh pull-apart basin. The geometrical relationship between the active fault trace and the older fault traces suggests that the basin may have evolved in a two stage process in which the original releasing fault bend developed a cross-cutting fault, accommodating most of the subsequent strike-slip displacement. The role of the YF in controlling basin evolution is further supported by the correspondence of the active fault with the boundary of the present depocentre. Our results highlight the interrelation between active strike-slip faulting and the coseismic incremental evolution of fault-related sedimentary basins, which may provide a conceptual model with broader implications on analogous tectonic systems worldwide.