Analyses of seismicity parameters of the August 11th, 2012, Ahar-Varzaghan earthquakes in north-western Iran

Abstract

North-western Iran (Azerbaijan province), one of the most seismic regions of the country, has experienced many seismic events during its long history. The recent dual earthquake with Mw = 6:4 and Mw = 6:3 struck the Ahar-Varzaghan area in Azerbaijan province in 2012.8.11 and caused a lot of fatalities. In this paper, the varieties of several seismic parameters, such as the b-value of the Gutenberg-Richter relation and standard deviation, Z, have been investigated to explore the temporal and spatial changes of seismicity patterns. Calculating and comparing these data before and after the occurrence of earthquake demonstrate some information about anomaly preceding main shocks. Temporal variations of b-value show a clear decrease before the 2012 Ahar- Varzaghan dual earthquakes. Considering the spatial changes in the b-values, it is possible to recognize a zone with abnormal low b-values around the epicenter of these events. The variation of the b and Z-values around the epicenter shows preparedness of the region before the occurrence of the main shock of Ahar-Varzaghan earthquake.