Some Aspects about Seismology of 2012 August 11 Ahar-Vaezaghan (Azarbayjan, NW of Persia) Earthquakes Sequences

Abstract

In 2012 August 11 (12:23 UTC) a moderate earthquake with MW=6.4 (USGS) occurred between Ahar and Varzaghan towns in Azarbayjan Province at northwest of Iran. After eleven minutes another earthquake shook the area with MW=6.2 (USGS). These consecutive earthquakes followed by intensive sequences of aftershocks whereas the strongest one had MW=5.3 (USGS). In data processing including depth modification and focal mechanism solution, we used regional (Institute of Geophysics, University of Tehran (IGUT) and International Institute of Earthquake Engineering and seismology (IIEES) of Iran) and worldwide (ISC) seismological data. After processing westward fault propagation estimated using Building and House Research Center (BHRC) of Iran strong-motion records. Also depth of the mainshocks and some important aftershocks modified using pP phase travel times recorded with ISC stations (10-14 km) which are nicely situated in seismogenic part of crustal structure of the area. The focal mechanisms processed using first P motion method for the two mainshocks and dominant mechanisms calculated for the intense aftershocks (MN>4.0, IGUT) manifestly displayed a strike-slip movement on a steep south dipping nodal plane with near E-W strike without any interpretation using earthquakes location. These are associated with the Geological Survey of Iran (GSI) field observations.