Volkan Karabacak, Uwe Ring, I. Tonguç Uysal

In the easternmost segment of the North Anatolian Fault (NAF) zone there are discrepancies in earthquake characteristics arising from differences between geodetically determined and geologically observed slip rates. We investigated the spatial distribution of deformation across a NAF fault segment, Turkey. Field observations were conducted on the offset of physiographic features along the principle fault and on a carbonate-filled fissure system a few hundred meters away from the main slip zone. Considering the rheology of the geological units, we propose distributed deformation across the principal fault strand in a stretching zone causing sigmoidal simple-shear rotation of the carbonate-filled fissure system. Since the fissure system is made up by previously dated alternating carbonate bands formed during distinct rupture events, the sigmoidal deformation provides an opportunity to understand the off-fault deformation rate in the stretching zone. Comparing displacement data of the sigmoidal carbonate vein with isotopic age results indicates an off-fault deformation of 15.72±2.83 mm per year for the Holocene, which corresponds to at least 50% of the geodetically estimated annual slip across the fault. The results indicate that distributed deformation needs to be taken into account in terms of the discrepancies on earthquake characteristics of active fault systems.