Evidence of active faulting in the Azarshahr-Tabriz fault zone of northwestern Iran

The 1641 Dehkhwargan-Tabriz earthquake (Ms 6.8) is the only destructive earthquake to have occurred in Azarshahr-Khosrowshahr-Osku region of northwestern Iran. Ambiguities regarding the causative fault of this earthquake were a motivation to someway declare its mechanism. In this study, by conducting a field survey in an area between Tabriz and Azarshahr, and use of satellite imagery and aerial photographs, we provide geologic and geomorphic indications to identify the poorly known Azarshahr-Tabriz fault zone (ATF), which passes through the meizoseismal region of the 1641 earthquake. Our observations highlight the presence of a sinistral active fault zone that extends ~40 km in length from south of Tabriz to the northeast and north of Azarshahr to the southwest. The ATF is a structural assemblage of several fault strands with a variety of extensional and compressional mesoscale structures. We estimated slip rates ranging from ~0.01 mm yr−1 to 1 mm yr−1, based on drainage offset measurements, which demonstrate a relatively stable tectonic environment located immediately south of the well-known seismically active dextral North Tabriz fault.