Strain partitioning of active transpression within the Lebanese restraining bend of the Dead Sea Fault (Lebanon and SW Syria)

Abstract

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.

Measurement of Anomalous Radon Gas Emanation Across the Yammouneh Fault in Southern Lebanon: A Possible Approach to Earthquake Prediction

“…1, represents the most important structure because it connects the southern and the northern parts of the DSFS. This fault has a strikeslip displacement of 4-6 mm year -1 , while the Roum Fault shows a strike-slip rate of 1 mm year -1 Daeron et al 2004;Nemer and Meghraoui 2006;Gomez et al 2007). A recent study by Gomez et al (2007) showed that the Yammouneh Fault accommodates most of the expected strike-slip motion, which indicates that this fault is accumulating strain.…”

“…This fault has a strikeslip displacement of 4-6 mm year -1 , while the Roum Fault shows a strike-slip rate of 1 mm year -1 Daeron et al 2004;Nemer and Meghraoui 2006;Gomez et al 2007). A recent study by Gomez et al (2007) showed that the Yammouneh Fault accommodates most of the expected strike-slip motion, which indicates that this fault is accumulating strain. These authors deduce that the fault's present day lack of seismicity is likely a reflection of the slow rate of strain accumulation in a locked fault system.…”

“…2). The choice of the El-Khiam basin, which is located on one segment of the Yammouneh Fault, for measurement of temporal radon variability, is based on the fault's seismic activity (Gomez et al 2007), and the required homogeneity of the soil cover present in this location. In addition, the content of Ra-226 in the fault zone and its correlation with the measured Rn emissions can be evaluated.…”

“…The geological nature and structure of DSTF has been investigated by many researchers worldwide (Walley 1988;Butler et al 1998;Butler and Spencer 1999;Beydoun 1999;Meghraoui et al 2003;Gomez et al 2003Gomez et al , 2006Gomez et al , 2007. In addition, studies of the seismicity and tectonic activity of the DSTF, including its branching faults within Lebanese territory, have been carried out by Mohamad et al (2000), Gomez et al (2001), Tapponnier et al (2001), Meghraoui et al (2003), Nemer and Meghraoui (2006), Reilinger et al (2006), Nemer, Meghraoui et al (2008), Alchalbi et al (2009), and Palano et al (2013).…”

“…The variability of radon gas concentrations due to seismic activity along a fault plane boundary shows positive results related to the stress and strain behavior of the faults. Careful study of this relationship can be a way to verify stress/strain and energy accumulation along the Yammouneh Fault system, as stated by Gomez et al (2007).…”