Geometrical and seismic parameters of the Qoshadagh fault and its role in evolution of the Sabalan Plio-Quaternary Volcano (Northwest of Iran)

In order to evaluate seismic hazard along Qoshadagh Fault (QDF, the causative fault of 11 Aug. 2012 Varzegan- Ahar earthquake), geometric and seismic parameters of the fault were investigated. QDF consists of a central E-W striking, dextral-reverse segment terminating at both ends into NW-SE striking splay arrays. Both eastern and western splay arrays form locally transtensional bends. The NW-SE striking splay faults form a large-scale transtensional horsetail pattern cutting through young lava flows of Mount Sabalan. The eastern segment of the Qoshadagh Fault has undergone local transtension and played an important role in the volcanic activity of Mount Sabalan. The extensional component of the splay fault pattern may have facilitated upper crustal magma migration and installation of the Sabalan Volcano. Volcano-sedimentary and lahar deposits have recorded syn-depositional normal faulting and soft-sediment extensional structures. The NW-striking fault splay has displaced dextrally the caldera wall by 720 ± 25 meters. The published 301 ka and 545 ka U-Pb zircon ages of ignimbrites associated with the collapse of the caldera (Ghalamghash et al- 2016), allows calculation of an average slip rate of 1.9 ± 0.6 mm.yr-1 over the past 500 ka. Combining the morphotectonic, fault slip, and timing and correlating of identified events in excavated paleoseismic trenches, we obtained an average rate of 1.7 ± 0.2 mm.yr-1 for the central QDF.