Stress partition on the Palu-Koro fault controlling the 2018 Mw 7.5 Palu earthquake and its seismic hazards

Abstract

The Mw 7.5 Palu earthquake struck the Palu-Koro fault on September 28, 2018 in the Sulawesi Island, Indonesia. Previous studies suggested that the predominantly unilateral southward rupture of this earthquake unzipped the central part of the Palu-Koro fault. Two seismic gaps were left to the north and south ends of the Palu-Koro fault. To date, the cause for earthquake generation has yet to be investigated. As a result, the reasons behind the earthquake rupture's southward unilateral propagation and termination remain unclear. The hazards of the two seismic gaps at the north and south ends of the Palu-Koro fault have yet to be explored. As such, the present study calculated the Coulomb stress change that was induced by historical large earthquakes within the target region. The stress partition and evolution on the Palu-Koro fault were examined before and after the 2018 Palu earthquake. We found that the 1996 earthquake (Mw = 7.9) on the Minahassa thrust triggered the 2018 Palu earthquake by promoting stress at the epicenter of the 2018 earthquake. The stress shadow close to the north of the epicenter of the earthquake acted as a stress barrier by preventing the earthquake northward rupture. However, the southward earthquake propagation was terminated by the stress shadow to the south of the rupture. These stress shadows were caused by the historical earthquakes on the Palu-Koro fault. Stress promotions in the two seismic gaps of the Palu-Koro fault produced by 2018 Palu earthquake have resulted in increased seismic and tsunami hazards, calling close attention to hazard prevention in central Sulawesi. Our results are important for understanding the stress migration and the induced seismic activity in the thrust and strike-slip faults system globally.