Microseismicity and seismotectonics around the Mosha fault (Central Alborz, Iran)

Abstract We present the results of a microearthquake study conducted during 5 months of 2006 with 44 portable seismological stations around the Mosha fault, the most prominent structure located east of Tehran, where several major earthquakes occurred during the historical time, in the Central Alborz (Iran). We recorded 538 earthquakes at more than 4 stations. Among these earthquakes, 148 were located with statistical uncertainties (ERH and ERZ) less than 3 km, a gap less than 180° and RMS less than 0.3 s. We also present the seismicity recorded by the Institute of Geophysics of the University of Tehran from May 1996 to July 2008. IGTU recorded almost 13,000 events during this time, 4428 were recorded in more than 4 stations and 599 with the same criteria as for the temporary network. Most earthquakes are located along the Mosha fault at depths ranging between 0 km and 20 km, with a maximum between 10 and 15 km, as it does at most of the other faults in Central Alborz. Cross-sections clearly show the Mosha fault, in its central part, dipping northward at an angle of 70°. We computed also 51 focal mechanisms. Most of them show left-lateral strike–slip motion associated with the Mosha fault. A few mechanisms, located south of the Mosha fault are consistent with normal faulting.