The Zandjan fault system: Morphological and tectonic evidences of a new active fault network in the NW of Iran

The Zandjan province is situated in the NW of Iran, at the junction between the southern termination of the Tabriz right-lateral strike-slip fault and the western end of the Alborz active mountain range. Despite this key location, in terms of active tectonics, there is no destructive earthquake reported in available historical seismicity catalogues. Even if a few low magnitude instrumental earthquakes have been recorded indicating that this area is actively deforming, the Zandjan region can be considered as a seismic gap. Based on detailed field investigations, digital elevation models (DEMs), satellite image and aerial photo interpretations, we have identified a major active fault network affecting this regions. It is mainly constituted by several west and est verging thrust faults, trending NW–SE to N–S, that clearly cut Late Quaternary to Holocene deposits. Evidences in the morphology indicate also that they accommodate some right-lateral slip component. This fault network can be divided into four major fault zones affecting Zandjan city (present day population over 500,000) and part of the Zandjan–Mianeh basin more to the west. Based on fault geometrical characteristics (fault length, segmentation…) and kinematics, the Zandjan fault system is certainly capable to produce moderate to large earthquakes (Mw = 6.5–7.0) and serious damages in the Zandjan city and surrounding areas. The study of these faults is, then, of major interest for seismic hazard assessment in Zandjan province where total population exceed 1.5 million but also to better understand present day geodynamic of NW Iran.

Research Highlights
► We identified and studied in the field a new fault network in NW Iran.
► The Zandjan fault network is mainly composed of NW–SE active thrust faults associated to right-lateral strike-slip faults.
► These active fault zones join together in the immediate vicinity of Zandjan City.
► Strong to moderate earthquakes could affect the town of Zandjan and surrounding region (up to 1.5 million people).