The 2021MW 6.2 Mamuju, West Sulawesi, Indonesia earthquake: partial rupture of the Makassar Strait thrust

On the 2021 January 15 (local date), an MW 6.2 earthquake struck the Mamuju and Majene regions of West Sulawesi, Indonesia. This event killed more than 100 inhabitants, leaving at least 30 000 people displaced from their homes, and damaged almost 8000 buildings within a radius of ∼30 km from the main shock's epicentre location (as shown on our damage proxy map). This event was generated by an active fault that continues to the Makassar Strait Thrust (MST) offshore West Sulawesi. The hazard potential of this fault remains poorly understood. In this study, we use seismic and Global Positioning System (GPS) data to investigate the source characteristics of the main shock. The results suggest that the main shock partially ruptured one segment of the MST, activated a secondary fault structure, and likely brought the updip unruptured section of the MST segment closure to failure. Our analysis of interseismic GPS velocities indicates that the Mamuju and Majene regions have a higher crustal strain rate than other nearby regions. The results (partial rupture of the MST segment, the updip unruptured section of the MST and high strain rate in the Mamuju and Majene regions) together suggest a significant seismic hazard potential in West Sulawesi, particularly in the Mamuju and Majene areas.