Updating the geometry of the saluki segment: bayesian moment tensor analysis of the 2012 M_W6.3 palu, indonesia, earthquake and implications for coulomb stress transfer

The Palu-Koro Fault System in central Sulawesi, Indonesia, is known to produce medium-to-large earthquakes, including the M_W6.3 event on August 18, 2012, and M_W7.5 event in 2018. However, the subsurface fault geometry, particularly its dip angle, remains poorly constrained, which may lead to an underestimation of stress transfer and inaccurate hazard assessments. In this study, we performed Bayesian moment tensor inversion on 19 focal mechanisms (M_W≥ 3.8) from the 2012 M_W6.3 earthquake sequence to update the geometry of the Saluki segment within the Palu-Koro Fault System. The analysis yielded a dip angle of 83°±4.5°, a rake of 7.33°±5.52° (left-lateral strike-slip), and a 345.2°±3.87° strike (NNW–SSE). This geometry substantially influenced the Coulomb stress change calculations, producing a ~ 300 kPa (3 bar) decrease in the maximum stress; however, polarity reversals in 12 of the 54 Saluki subfaults were observed in this study. The stress redistribution from the 2012 event predominantly affected the Saluki segment, along which gentle dips produced broader stress perturbations. Although the Palu-Saluki zone accumulated significant stress, the Makassar Strait segment (i.e., where the 2018 rupture occurred) exhibited limited seismicity after 2012, which suggests that its failure required additional stress contributions beyond the transfer that occurred in 2012. Nevertheless, These results underscore that even moderate adjustments to fault geometry (e.g., dip) can substantially influence stress interpretations and hazard assessments.