Focal mechanism of the August 18th 2012 Mw6.3 Palu-Koro earthquake and its implication of seismic hazard

The Palu-Koro fault is a left-lateral strike-slip fault in Sulawesi within the active triple junction generated by the ongoing fast convergence of the Pacific-Philippine plate, the Indo-Australian plate and the Sunda plate. There are densely populated areas that are susceptible to earthquakes occur along the fault, and the August 18th 2012, Mw6.3 earthquake is one of such events. To better understand this earthquake and the seismic hazard in the region, we estimated source parameters of this earthquake using the Cut and Paste (CAP) inversion method with regional broadband waveform data. Our results show that the best solution of this event is 339°, 71°, −16° and 11 km for strike, dip, rake and centroid depth, respectively. Inversions using stations within different distance ranges, i.e. 0-5, 0-10° and 0-20°, reveal consistent solutions, suggesting the robustness of our result, which is also in agreement with that from the other agencies, i.e. USGS and Global CMT. We further verify the centroid depth by modeling the depth phases recorded at the teleseismic distance, which also confirm the depth of 11km. Finally we analyzed the Coulomb stress caused by this earthquake and historical events to investigate the interaction between the earthquakes in the region. Our analysis also shows that the unclamping effect from the 1996 Mw7.9 megathrust in the Minahassa Trench promoted the occurrence of the 2012 Mw6.3 event. High slip-rate across the fault and Coulomb stress analysis suggest that more attention should be paid to the segments along the Palu-Koro fault that did not rupture in the previous earthquake circle.Published versio