TEMPORAL VARIATION OF VP / VS AS A PREQURSORY IN AUGUST 11 , 2012 AHAR – VARZAQHAN EARTHQUAKE

On August 11, 2012, two earthquakes of Mw = 6.5 and Mw = 6.3 took place in part of the Western Alborz seismotectonic province, Ahar-Varzaqhan region.We processed the phase data recorded in 8 seismic stations during 2006-2012 using Wadati method. Temporal variations of Vp/Vs were studied as a tool in earthquake precursory researches in these earthquakes. We impose a number of restrictions on the computation. The number of stations involved in this process is more than 3 and recorded earthquakes with M ≥ Mc. Under these restrictions, the study shows that Vp/Vs in and around Ahar-Varzaqhan study area normal-low-normal process a few months before main shock occurrence.