Morpho-tectonics and geoelectric method applied to active faults characterization in South of Mashhad Plain, Northeast of Iran

Mashhad city, the second most populous metropolis of Iran, with a population of more than three million, lies between two seismically active regions of Binalood and Kopet-Dagh. In recent years, the city has grown around the South Mashhad (SM) fault zone in the south. Given the vital role of the SM fault in influencing the seismic risk of the city, this study is aimed at the evaluation of the fault’s characteristics and activity. The overall trend of the fault and evidence of its activities are investigated by morphotectonic studies, and the situation of fault zone was explored by different geophysical methods including resistivity, magnetic and microtremor array. Morphology studies have shown that SM fault results in the deviation of the river channels, replacement, and deformation of alluvial fans. The geoelectric studies have shown three segments of the fault, F1, F2, and F3, with the notable normal displacement. Magnetometry and microtremor array studies across F1 confirmed the normal displacement of the fault. It is concluded that SM fault is an active right-lateral and normal fault system that had a significant role in the development of Mashhad Valley.