Spatial and Temporal Stress Changes in the Aftershock Sequence Following the Nov. 12, 2017 Sarpol-e Zahab Earthquake

A devastating earthquake with moment magnitude of 7.3 hit Sarpol-e Zahab in the Zagros on November 12, 2017. An intense aftershock sequence was recorded by the permanent and dense temporary seismic networks, which installed rapidly in the epicentral region. The focal mechanisms of the November 2017 aftershocks were gathered (for about 50 events) and derived (for about 10 events) from P-wave polarities and/or waveform modeling, show predominantly thrust movements. The transpressional stress regime in the region is suggested as the driving force for the earthquakes. The temporal variation of the principal stress directions analyzed by subsequent stress inversion in several time intervals following the Nov. 2017 mainshocks. In addition, the spatial stress variations were studied implementing the stress tensor inversion in different clusters of events. These results suggest that the 2017 mainshock ruptures caused both spatial and temporal stress perturbations that continued in time showing a specific character, which was not observed before in the Zagros region.