Bayesian Moment Tensor Analysis of The 2012 Mw 6.3 Palu Earthquake Sequence for Updating The Palu-Saluki Segments and Its Impact on Coulomb Stress Distribution

Abstract

The Palu-Koro fault, part of the Central Sulawesi fault system, has produced many large earthquakes (Mw > 6). Palu earthquake on 18 August 2012 (Mw 6.3) which occurred close to the largest earthquake ever recorded in Central Sulawesi, the Donggala earthquake on 28 September 2018 (Mw 7.5), also caused notable damage around Palu, the capital of Central Sulawesi, Indonesia. We infer 16 earthquake events of magnitudes ranging from Mw 3.9 to 6.3, which occurred between 18 August and 31 December 2012 by applying Bayesian moment tensors inversion and get criteria A and B, using catalogue and waveform data from Meteorology, Climatology, and Geophysics Agency (BMKG) regional stations. Our results show that the 2012 earthquake sequence showed a left-lateral strike-slip mechanism, with the mainshock located west of Lake Lindu. Many aftershocks were distributed near the northern end of the Saluki segment of the Palu-Koro Fault. The inferred solution has strike of North-Northwest to South-Southeast and a dip angle of about 82.5°, updating vertical fault from National Earthquake Center (PusGeN). After Calculating the change in Coulomb stress on the fault using a new geometry based on the moment tensor solution, we find that the model shows larger stress changes, up to 5 bars, with a wider impact area compared to vertical fault. Hence, updating the geometry of the Palu-Saluki Segment is important in constructing seismic hazard analyses in the region.