The Effect of Ground Condition on Seismic Amplification in the 2021 Mamuju Earthquake Sulawesi

A shallow earthquake occurred in the West Sulawesi Province of Sulawesi Island, Indonesia, with a moment magnitude (Mw) of 6.2 on January 15, 2021, at 02.28 local time. The epicenter of the earthquake was in Majene, ~ 32 km from the provincial capital, Mamuju. The earthquake was caused by the tectonic movement of the Makassar Strait Thrust fault, leading to thousands of buildings being damaged and hundreds of people dying in the city of Mamuju. The objective of this study was to investigate the relationship between ground conditions and large seismic amplification that might occur. Therefore, a series of geotechnical investigations were undertaken. Non-linear and equivalent linear site-specific response analyses were also conducted to model the estimated ground response propagated by earthquakes. Our findings suggested that the earthquake generated a large seismic amplification due to the ground conditions in the city. The computed seismic amplifications were 1.4–2.67 in the period of 0.4–2 s, which coincided with the resonant periods of two–five-story buildings in the city. These results would be beneficial in mitigating the seismic hazards in the city, in the near future.