the pattern and kinematics of deep deformation of 2012 ahar-varzaghan earthquake doublet (mw 6.4 and 6.2), a new seismotectonic interpretation

The 11th august 2012 ahar-varzaghan earthquake doublet mw 6.4 and 6.2 occurred near the city of ahar, northwest iran, in aregion where there was no major mapped fault or any well-documented historical seismicity. to investigate the active tectonics andthe state of pre and post-seismic stress distribution of the source region, we applied a combination of coulomb stress change, b-valuemapping, and the fry method. inferred coulomb stress field reveals the e–w-striking (dextral) fault responsible for the first eventand the nne–ssw-striking (sinistral reverse) fault for the second event. the high slip stress-released regions in the obtained b-valuemap and the dominant anisotropies of aftershocks on regional stress-parallel cross-sections achieved by the fry method, together withthe distribution of aftershocks mechanisms, merely highlight the particular wedge-shaped structures namely the rhombic structures.the clockwise block rotation about the vertical axis under the right-lateral regional shear between the kura basin to the north and thecentral iranian block to the south and nw-oriented coeval shortening leads to the formation of rhombic structures. the results ofthis study improve our understanding of the kinematics of active deformation in nw iran and have important implications forseismic hazard assessment of the region and potential future failure area.