Tsunami scenario triggered by the activity of the Mentawai Fault Zone offshore western Sumatra Island

Abstract

Subduction zones worldwide pose tsunami risks, mainly linked to megathrust activity near subduction trenches. However, tsunamis can originate from various sources, including marine volcanic eruptions, submarine landslides, and strike-slip earthquakes. In the Sumatra subduction zone, a seismic gap in the Mentawai region heightens the tsunami risk. This region’s tectonics are complex due to the oblique subduction of the India-Australia oceanic plate beneath the Eurasian continental plate, leading to the sliver faults system of Mentawai Fault Zone (MFZ) and Sumatra Fault Zone (SFZ). The SFZ on Sumatra Island has limited tsunami potential, except at its northern and southern offshore extensions. In contrast, the MFZ, situated in the marine Northern Bengkulu basin, holds a higher tsunami-generation potential. This study aims to assess the MFZ activity in generating tsunamis, estimate the maximum wave height, and analyze propagation, and arrival times at several crucial sites in Western Sumatra Province. We utilized the COMCOT tsunami model to simulate scenarios with two fault mechanisms, i.e., strike-slip and back thrust, and two magnitudes (Mw 7.6, and 8.2). The results indicate that the most hazardous tsunami, generated by a strike-slip fault with Mw 8.2, produces a 2-meter tsunami on the east coast of Siberut Island and the west coast of Padang City, West Sumatra. The scenarios reveal that Mentawai Island’s eastern part lacks evacuation time, with an almost instantaneous tsunami arrival. In contrast, western Sumatra, including Pariaman and Padang City, has 13 to 20 minutes for evacuation planning. Thus, disaster risk reduction strategies in these locations should consider these findings.