Source parameters and slip distribution of the 2018 Mw 7.5 Palu, Indonesia earthquake estimated from space-based geodesy

Abstract

The 2018 Mw 7.5 Palu earthquake is one of the most geometrically complex events ever recorded on Central Sulawesi Island. It caused devastating tsunamis and landslides after the mainshock, resulting in great casualties and damages to the infrastructures in Palu city and surrounding areas. In this study, we combined far-field InSAR, near-field SAR and optical sub-pixel correlation data to determine the fault geometry, source parameters and fault-slip distribution of this event along the Palu-Koro fault zone. Our best-fitting fault model contains three fault segments with variable strike angles, showing that the coseismic rupture is dominated by a left-lateral strike-slip motion accompanied by minor normal-slip and reverse-slip components. On the onshore segments, the maximum slip is up to ∼ 8.4m with a left-lateral strike-slip component of ∼ 6.8m at a depth of 4km on the central segment near Palu city, a normal-slip component of ∼ 4.3m in the left releasing step-over and a reverse-slip component of ∼ 3.2m in the offshore area near the Palu bay. On the offshore segment, the maximum slip is up to ∼ 4.2m with a normal-slip component of ∼ 1.8m. We argue that the offshore reverse-slip motion might have played a key role in the generation of the Palu tsunami. We also suggest that the linking normal segment contributed to the rupture propagation across the left releasing step-over from the central segment to the southern segment, while the linking reverse segment arrested the rupture propagation across the right restraining step-over to north. The Coulomb stress change reveals that there is possibility of future great earthquakes occurring on several major faults in the northeast of Palu city. Our results have great significance to qualitatively assess the risk of future seismic hazards in such a geometrically complex fault system.