Mechanism for seismic supershear dynamic rupture based on in-situ stress: a case study of the Palu earthquake in 2018

Abstract

The Palu earthquake, with a magnitude of 7.5, severely devastated the region in Central Sulawesi, Indonesia, but the mechanism of dynamic rupture considering in-situ conditions is not well understood. The in-situ stress field and fault geometry play important roles in the evolution of the supershear rupture. This study investigated the in-situ stress field, critical factors including the inversion of principal stress orientation by the focal mechanism solution, and constraint magnitude using the improved lateral pressure coefficient polygon. Furthermore, the dynamic rupture process is simulated using the finite element method (FEM) considering the strike and in-situ stress magnitudes of the seismogenic fault. The result shows that the principal stress orientation rotates counterclockwise about 15° from north to south, and the northern part of the fault zone is less straight than the fault from Palu Bay to the south, which are two decisive factors for supershear in the north. The damage zones considering the peak acceleration and co-seismic displacement are enlarged in Palu City, which is attributed to the rupture mode. It provides plausible explanations for this supershear event and sheds light on different dynamic rupture processes and seismic hazards that can be predicted by fully understanding the regional in-situ stress field.

Keywords

• Supershear rupture
• in-situ stress
• focal mechanism solution
• shape ratio
• Palu earthquake