Source study of 2017 Hojedk triplet earthquake sequence, southeast Iran

Abstract

In December 2017, a triplet earthquake sequence of Mw 5.8–6.1 occurred near Hojedk, southeast Iran. The sequence was not destructive, but occurred in a highly seismically active region that previously experienced the 1981–1998 Sirch-Golbaf earthquake sequence and destructive 2003 Mw 6.6 Bam earthquake. We apply a waveform inversion method based on the modeling of regional seismic broadband data to derive the point source and kinematic rupture parameters of the triplet and its five significant aftershocks. The choice of an earthquake source model with a reduced number of parameters and a sequential inversion process with several iterations result in unique and stable earthquake source solutions. Within the inversion process, we combine the modeling of low- and high-frequency seismological data to retrieve the moment tensor and the kinematic source parameters. Synthetic seismogram and spectra are generated for an accurate regional velocity model. Our results suggest that the triplet ruptured a segmented fault system, with centroid locations aligned along a single lineament. Estimation of rupture directivity suggests the activation of SE-NW structure. In conclusion, we suggest that the triplet was associated with the failure of one or more aligned blind thrust faults, oriented SE-NW and dipping to the NE, in a restraining bend between strike-slip faults in a region that is a part of the greater system of the present continental shortening in Iran.