Seismotectonic investigation in northwest Zagros, Iran: analysis of Ezgeleh Mw 7.3 aftershocks

Zagros, on the Alpine-Himalayan belt, has undergone significant tectonic tension due to the convergence of the Arabian and Eurasian plates, resulting in numerous faults, folds, and thrusts. Despite extensive research, uncertainties persist regarding its seismotectonic features and active faults. This study aims to identify causative faults for earthquakes within this region by calculating focal mechanisms of 47 earthquakes that occurred in northwest Zagros and examining seismicity at depth. In this pursuit, 12 cross-sections have been delineated within the region. The spatial distribution of earthquakes within these sections, coupled with the computed focal mechanisms, serves as indicators of the causative fault. The study attributes a significant proportion of the recorded earthquakes to different segments of the Mountain Front Fault and estimates the length of some segments to exceed what is depicted in geological maps. Clear trends in the depth distribution of earthquakes and alignment of some features with previous studies suggest the activity of hidden faults and the influence of an arc in the study area. The collective results provide a comprehensive understanding of the proposed arc, further reinforced by the identification of a strike-slip fault intersecting the High Zagros Fault, serving as tangible evidence of the arc’s existence.