Aftershocks properties of the 2013 Shonbe Mw 6.3 earthquake, central Zagros, Iran

Abstract

The spatial and temporal seismicity parameters, stress state as well as the partitioning of the seismic energy of the Shonbe earthquake sequence have been investigated. The geodetic data and the stress tensor inversions of the focal mechanisms before and after the Shonbe main shock indicate the same NE–SW trend of the greatest principal stress. This stress orientation demonstrates a non-heterogeneous stress state in that region of the central Zagros which can be confirmed by the fractal dimension and the estimated p-value. The aftershock focal mechanisms show a diversity which may be associated with the approximately uniaxial stress field acting nearly perpendicular to the main-shock fault plane in which the co-seismic stress release is nearly complete. The spatial distributions of the b and p-values have been investigated and compared. The high p-value regions (e.g. far to the southeast, south and southwest of the main shock) are approximately consistent with the high b-value regions and the low p-value regions (e.g. the limited areas at the north- northeast of the main shock) are nearly consistent with the low b-value regions. The limited areas surrounding the main shock and also at the east-southeast of the main shock the p-values are not in agreement with the b-values which may be attributed to the local tectonic features in those regions. The seismic moment ratio and the Bath’s law have been used to constrain the energy partitioning between the main shock and the aftershocks. It is found that a high fraction of the energy is released by the Shonbe main shock and nearly one third of the energy released by the aftershocks. This may be associated with the high stress imparted by the blind thrust main shock to the overlying crust in which promotes failure in the surrounding area and is often relieved by secondary faults and typically produce a high number of aftershocks.