Coseismic slip distribution of the 14 January 2021 Mamuju-Majene, Sulawesi, earthquake derived from GPS data

The 14 January 2021 Mw 6.2 Mamuju-Majene earthquake occurred in West Sulawesi, Indonesia, preceded by three earthquakes with Mw 5.7, Mw 5.2 and Mw 4.3. The fault responsible for the mainshock remains an enigma. Using static Global Positioning System (GPS) data surrounding the epicentre, we estimated the coseismic displacements of the mainshock. Significant coseismic displacements were estimated at stations located northward and southward from the epicentre. Inversion of GPS data was performed along with two possible fault sources; they are the Makassar Strait Central fault and the Mamuju fault. While the Makassar Strait Central fault is an offshore sloping fault where the location of the most southern segment of the fault is in off the western coast of the Mamuju region, the Mamuju fault is a nearshore fault that runs northward from off the western coast of Majene to Mamuju. During our investigation, we found a larger misfit between GPS data and the resulting model on the coseismic slip modelling along the Makassar Strait Central fault. We also found that the Coulomb stress change using the coseismic slip along the Mamuju fault model explains aftershocks better than the other models. This study suggests that the 2021 Mamuju-Majene earthquake occurred along the bending fault plane of Mamuju fault with the cumulative seismic moment of four earthquakes occurred on 14 January 2021 is 6.6 × 1018 N·m, or equivalent to Mw 6.4.