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

Abstract

Summary On the 15th of January 2021 (local date), an MW 6.2 earthquake struck the Mamuju and Majene regions of West Sulawesi, Indonesia. This event killed more than one hundred inhabitants, leaving at least thirty thousand people displaced from their homes, and damaged almost eight thousand buildings within a radius of ∼30 km from the mainshock'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 mainshock. The results suggest that the mainshock partially ruptured one segment of the MST, activated a secondary fault structure, and likely brought the up-dip 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 up-dip 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.

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