The Coulomb Stress Changes and Seismicity Rate due to the 1990 M w 7.3 Rudbar Earthquake

We investigate correlation between the Coulomb stress changes and the spatial distribution of the aftershocks of the 1990 Mw 7.3 Rudbar earthquake that occurred on and off the Rudbar fault. The Coulomb stress changes indicate that the Rudbar mainshock encouraged parts of the Kelishom and Kashachal strike-slip faults (located east of the main rupture), as well as parts of the Manjil Thrust fault (located south of the main rupture). The central part of the Manjil Thrust, which is sandwiched between two stress shadow zones, experienced an increase in Coulomb stress. We observe that the events before and after the Rudbar mainshock have different spatial distribution patterns. We find that most of the aftershocks occurred in an area between the Kabateh and Zardgeli segments where the static Coulomb stress is high, while few aftershocks occurred in the stress shadow zone that extends to the northwest and southeast of the Rudbar rupture. The aftershocks that occurred in the stress shadow zones at the northwest of the Baklor segment were related to the continuation of the background seismicity after the mainshock. A burst of seismicity following the Rudbar earthquake at the south of the Zardgeli segment provides evidence for dynamic stress triggering for the aftershocks that affected these region for first 1–3 months after the mainshock. We also compare the Coulomb stress changes with the seismicity rate and find the regions with high seismicity rate are in good agreement with the high stress such as is found in the western end of the Baklor and an area between the Kabateh and Zardgeli segments. To validate the effects of the Coulomb stress on the seismicity rate, we resolved stress changes on the aftershock nodal planes and recognize that the aftershocks located between the Kabateh and Zardgeli segments and the surrounding areas were brought closer to failure.

Coulomb Stress Changes; Seismicity Rate; Rudbar Earthquake