Coseismic Coulomb stress changes imparted by the 1996 Minahasa M w7.9 earthquake on the 2018 Palu M w7.5 earthquake and expected seismicity rate changes

The Mw7.5 Palu earthquake that occurred on September 28, 2018, in Indonesia caused much damage to the city of Palu. Preliminary investigations indicated that the Palu-Koro Fault (PKF) hosted this damaging event. We calculated the seismicity before and after the 1996 Minahasa Mw7.9 earthquake and found that the seismicity on the PKF was enhanced after this earthquake. The earlier earthquake added Coulomb stress changes (∆CFS) to the seismogenic fault plane. We calculated the ∆CFS produced by the Palu earthquake on a specified received nodal plane; the results suggest that many aftershocks occurred in the region of increased ∆CFS. This region was consistent with the region of increased seismicity. The ∆CFS on neighbouring faults increased, and up to 55.282 bar of stress was observed on the PKF. Furthermore, we calculated the expected seismicity rate and found that it will require ~50 years to recover to its original level.