Rupture characteristics of the 2012 earthquake doublet in Ahar-Varzagan region using the Empirical Green Function method

On August 11, 2012, within several minutes, two shallow destructive earthquakes with moment magnitudes of 6.5 and 6.4 occurred in Varzagan, Azerbaijan-e-Sharghi Province, in norhwest of Iran. In this study, the Empirical Green Function (EGF) method was used for strong ground motion simulation to estimate the source parameters and rupture characteristics of the earthquakes. To simulate the first earthquake, two aftershocks with magnitudes of 5.6 and 5.2 were used as the EGFs. In the second event, an aftershock with a magnitude of 5 was used as the small event. The size of the main fault caused by the first event was about 18 km in length and 10 km in width. Also, the size of the asperity in the second earthquake was about 16 km in the strike direction and 11 km in the dip direction. The durations of the ruptures in the first and second events were more than 9 and 10s, respectively. The estimated fault plane solution showed strike-slip faulting for the first earthquake and a reverse mechanism with a strike-slip component for the second one. Strike, dip and rake of a causative fault of the first and second earthquakes were determined as 270, 81 and 175 degrees and 230, 57 and 134 degrees, respectively. In addition, the stress drop in the first and second events was calculated to be about 22 and 34 bar, respectively.