A Comprehensive Assessment for the Aftershock Sequence of August 11, 2012 Varzaghan-Ahar Doublet Mainshocks, NW Iran

In this study, an evaluation of regional, temporal and magnitude properties of the August 11, 2012 Varzaghan-Ahar aftershock sequence was performed based on the different variables such as the Gutenberg-Richter b-value, the Modified Omori p-value, fractal dimension Dc-value and the maximum aftershock magnitude Mamax value which commonly used to describe aftershock behaviors. b-value was computed as 0.73 ± 0.03 for the study area where catalog has a completeness magnitude Mc = 2.0. This b-value is relatively small from typical b≈1 and it can be due to the abundance of aftershocks larger than Mw = 4 in the region. Structural heterogeneity of the seismic source along with the compressive stress situation of the aftershock area could be another reason for this finding as well. p-value was estimated as 1.00 ± 0.03 where c-value took 0.342 ± 0.106 according to the analysis which shows that the number of aftershocks of the Varzaghan-Ahar mainshock shows a relatively fast decrease. Dc-value was computed as 1.84 ± 0.07. This large value indicates homogeneously distributed aftershocks and more clustering in smaller areas or larger scales. As a result, the smallest b-values (< 0.7) and Mamax values larger than 5.0 were obtained around the mainshock. In addition, the biggest p-values (> 1.2) were found in and around the mainshock including Varzaghan. The areas having the biggest p-value and the lowest b-value have great coseismic deformation and stress, respectively. Hence, we can say that coseismic deformation and stress distributions are very effective on the b- and p-value changes. Thus, particular attention on assessing the aftershock hazard may be directed on the understanding of these spatio-temporal aftershock variables.