Stress triggering and aftershock properties induced by the Dalparri blind thrust fault at NW Zagros: The 18 August 2014 Mormori earthquake

Abstract

Abstract The Coulomb stress changes induced by the Mormori earthquake and their influences on the neighboring regions have been investigated. The central section of the Siah Kuh anticline and the southern section of the Kaseh Mast anticline have been encouraged to failure while, the Kabir Kuh anticline, the eastern and western sections of the Siah Kuh anticline and the northern section of the Kaseh Mast anticline have been inhibited from failure. A limited area of the positive Coulomb stress change zone on the top right of the Dalparri blind thrust has been detected in the cross-sectional view of the Coulomb stress changes that can be considered as the location of a back thrust. The Mormori aftershocks have been plotted on the stress change map and it is found that a little less than half of the events occurred in the increased Coulomb stress zones along the strike of the Dalparri anticline axis. Six out of nine large aftershocks with M ≥ 5 occurred in the positive Coulomb stress lobe. The estimated b-value map of the Mormori region has been compared with the Coulomb stress change zones and it is observed that the low and high b-value regions have some consistency with the positive and negative Coulomb stress zones near the north and northwest of the main shock, west of the Kaseh Mast anticline and the south and southwest of the western end of the Dalparri Fault, respectively. In contrast, the central and northern negative Coulomb stress change lobes have not consistency with the low b-values in these regions. By examining the modified Omori relation of the aftershocks, it is inferred that the moderate-fast decay rate in the Mormori region may be related to the local stress reduction due to the occurrence of several large aftershocks.