Frictional Fault Strength Analysis of Palu-Koro and Matano Faults, Sulawesi, Indonesia, from Earthquake Focal Mechanism Data

Sulawesi’s complex tectonic setting generates active Palu-Koro and Matano faults. Understanding earthquake mechanic is important for mitigation purpose. We performed fault strength analysis by examining its friction, through joint stress inversion and stress magnitude estimation approach, using focal mechanism data from International Seismological Centre bulletin. Friction was analyzed in four segments of the Palu-Koro Fault and two segments of the Matano Fault. Bootstrap and Jack-knife are applied to assess its uncertainty. From north to south, the friction pattern increases at the Palu-Koro Fault segments: Donggala (0.35<μs <0.56) to Palu segment (0.59<μs <0.76); then decreases sequentially: at Saluki (0.49<μs <0.55), Moa segment (0.31< μs <0.35), and further at the Matano Fault segment (Pamsoa-Ballawai) (0.26<μs <0.3). Regarding the 2018 Mw 7.5 Palu earthquake rupture, high friction at the Saluki segment coincides with and indicates its rupture termination. Seismicity records from 1977 to 2011 showed that the largest event occurred at Matano Fault has Mw less than 7.5. Low friction observed at Matano Fault correlates with small magnitude events and low fault strength.