Sequence signal processing of 2012 Ahar-Varzaghan earthquake (M-W 6.4) of NW Iran

摘要

Before starting seismic cycle of Ahar-Varzaghan 2012 event, a partial gap in the form of a pre-seismic calm sequence (seismicity rate, r = 0.46 event/year, b = 1.4) with duration of 303 days spatially has dominated over the entire seismogenic area. From April 17, 2012, to May 31, 2012, r significantly increased to 2.16, indicating strong foreshock sequence, and b value changed to 1.9, remarkably. In the last two months before the mainshock, foreshocks have partially migrated toward the earthquake fault (with a decrease in size, b = 2.0). Significantly, high rate of seismicity and low V-P/V-S (1.64) in the foreshocks sequence and also very high seismicity rate (17.3) and high V-P/V-S (1.76) in the aftershocks sequence make substantial differences between the seismic cycle and the background seismicity. Moreover, a significant E-W migration of the microseismicity was confirmed in the study area.