The Van Fault, Eastern Turkey: A Preliminary Geological Slip Rate

Abstract:

We present a preliminary quaternary slip-rate study on the Van fault, the source of the 2011 Mw7.1 reverse-slip earthquake which caused heavy damage to the cities of Van and Ercis, eastern Turkey. From the InSAR solution, we see a strong depth cut-off at 10km depth, above which there was no slip on the fault. We have carried out an investigation of the geomorphological expression of the fault in quaternary material, to determine whether the fault reaches the surface and, if so, whether this upper section could fail in an earthquake. On the western segment of the Van fault, we observe quaternary scarps coincident with the surface projection of the fault segment identified by InSAR, which displace quaternary alluvial fan and lake-bed deposits. These are coincident with the observation of fault gouge in quaternary deposits at a road cutting, providing evidence for a fault reaching the surface and suggesting that the upper section is capable of rupturing seismically. We use structure-from-motion photogrammetry, differential GPS and terrestrial LiDAR to determine offsets on two generations of fault scarps, and the creep offsets from the period following the earthquake. Preliminary radiocarbon and OSL dates from two uplifted terrace surfaces allow us to estimate a late quaternary geological slip-rate for the fault. Following the GPS and InSAR solution of Dogan et al. 2014 (GRL v41,i7), we also present field evidence and satellite image observations confirming the presence of a splay fault within the northern suburbs of Van city, which experienced creep following the 2011 earthquake. This fault is observed to be particularly evident in the early high resolution satellite imagery from the declassified CORONA missions, highlighting the potential for these datasets in identifying faults in areas now covered by urban sprawl. It remains unclear whether this fault could fail seismically. The fault which failed in 2011 is a north dipping reverse fault, unmapped prior to the earthquake. We identify similar geomorphological structures in the surrounding region, highlighting the need for further detailed tectonic mapping of the region.