Microseismicity and seismotectonics of the North Tabriz fault (Iran)

International audienceWe present the results of a microearthquake study conducted in 2004 with 31 portable stations around the city of Tabriz, which is crossed by an active fault and has experienced several destructive earthquakes in the recent history. From April 24 until July 24, we recorded 80 earthquakes by more than 4 stations. We complement these data with earthquakes recorded by the 8 permanent seismological stations of the Tabriz network operated by Institute of Geophysics of the University of Tehran from August 1995 until March 2008. Among a total of 6377 events, only 394 earthquakes were recorded by more than 5 stations and located with statistical uncertainties (ERZ and ERH) less than 5 km and a Gap less than 270°. Most of these earthquakes are located along the Tabriz fault, at a depth ranging from the surface to 20 km, comparable to other studies conducted in Central Alborz. We computed 22 focal mechanisms most of which show right-lateral strike-slip motion along east-southeast planes, consistent with the geologic evidence for Quaternary slip. We do not see any peculiar pattern near the Tabriz pull-apart basin, or at both ends of the North Tabriz fault, where it terminates in EW trending reverse faults. This suggests that the fault is simpler (more mature) at depth than at the surface