Relocation and Stress Analysis of the 2018 Mandali-Sumar Earthquake Sequence, Iraq-Iran Border

Abstract

The 2018 Mandali-Sumar earthquake sequence has started in January 2018 at the Iraq-Iran border within the Low Folded Zone of the Zagros Fold-Thrust Belt. To study the fault that is responsible for this earthquake sequence, the relocation of 32 earthquakes was conducted. In addition, moment tensor solutions of 9 large earthquakes were collected to know the fault motion and stress regime in the study area. The Computer Programs in Seismology (CPS) was used to analyze waveform data taken from 33 seismic stations located in Iraq and Iran to relocate earthquakes. The location of the earthquake sequence based on the IRSC bulletin shows a scattered spatial distribution, but the results of the relocations show that the earthquakes of the sequences are aligned in a longitudinal feature parallel to an anticline limb located in Ilam and Kermanshah provinces near the Iraqi border. The moment tensor solutions indicate that the sequence is related to a thrust fault with a 342º strike direction, 35º NE dip angle, and 76º rake angle. The TENSOR program was used to perform formal stress inversion of moment stress axes, which revealed that the azimuth of the maximum horizontal stress axis is 63º. The epicenters of the sequence are located between the Mountain Front Fault to the NE and the Zagros Foredeep Fault to the Southeast. We believe that the 2018 Mandali-Sumar earthquake sequence is related to displacement on the surface of the Zagros Foredeep Fault within the uppermost basement and the lowermost Phanerozoic cover.