Co-seismic stress transfer and magnitude-frequency distribution due to the 2012 Varzaqan-Ahar earthquake doublets (Mw 6.5 and 6.4), NW Iran

The Coulomb stress changes imparted by the 2012 Varzaqan-Ahar earthquake doublets to the surrounding area have been examined and correlated with the spatial distribution of the aftershocks. The stress changes due to the first main shock show that the western half of the South Ahar Fault, the southeastern half of the magnetic lineament ML1, the northeastern end of the ML2, the entire length of the ML3, a large part of the ML4 and the northeastern half of the ML5 were brought closer to failure. Whereas the entire length of the Khajeh Fault, a part of the North Tabriz Fault, the western half of the ML1, a large part of the ML2, the northwestern end of the ML4 and the southwestern half of the ML5 were moved away from failure. Along the length of the ML1, some aftershocks were clustered in the southeastern and central sections, while around the western section there is no earthquake clustering. The epicentral distributions of the aftershocks exhibit that most of the events were concentrated in the increased Coulomb stress zones. The b-value distributions in the map view and in the cross-sectional view have been investigated. The map view shows that the low b-value regions (e.g., the north-northwest, east-northeast and southeast of the main shock) are in good agreement with the positive Coulomb stress change zones. The crosssectional view indicates that the high b-value regions correlate with the areas of high co-seismic slip release. Therefore, surrounding the hypocenter and the western end of the first main shock fault have high b-values, more slip and positive stress drop, while the central sections of the fault have low b-values, less slip and negative stress drop. (C) 2016 Elsevier Ltd. All rights reserved.