ABSTRACTThe Coulomb Stress Changes Due to Rigan Earthquakes and their Aftershocks

On December 20, 2010, an earthquake with a moment magnitude of 6.5 has been occurred in south-east of Rigan in south of Kerman province. The second strong event was happened 37 days after the first event on January 27, 2011 with a moment magnitude of 6.2 in south-west of the first event. Previous studies indicated that the occurrence of an earthquake can change the distributed stress in surrounding region and caused triggering other events. We have calculated the coulomb stress changes due to the first earthquake in the hypocenter of the second earthquake in order to investigate the effect of first event on the second event. This study showed that the stress has increased about 2.8 bar (0.28 MPa) in the hypocenter of the second earthquake. Right-lateral displacement on the causative fault of the first event based on the tectonic and stress pattern of the region can be a cause of left-lateral displacement on the second event causative fault. Besides, in order to investigate the effect of the stress change on aftershocks distribution, we have calculated the coulomb stress changes due to these events on optimally oriented faults. Our calculations showed that more than 70 percent of these aftershocks distributed in places where the coulomb stress changes have been increased and have a positive amount. Coulomb stress changes due to these earthquakes on the surrounding right-lateral faults have been calculated and showed that the stress has been decreased on the central and north-west parts of bam fault and has been increased in the south-east part of this fault.