Abstract

Studies have indicated that submarine landslides played an important role in the 2018 Sulawesi tsunami event, damaging the coast of Palu Bay in addition to the earthquake source. Most of these studies relied on visible landslides to reproduce tsunamis but could still not fully explain the observational data. Recently, several numerical models included hypothesized submarine landslides that were taken into account to obtain a better explanation of the event. In this study, for the first time, submarine landslides were simulated by applying a numerical model based on Hovland’s 3D slope stability analysis for cohesion-frictional soils. To specify landslide volume and location, the model assumed an elliptical slip surface on a vertical slope of 27 m of mesh-divided terrain and evaluated the minimum safety factor in each mesh area based on the surveyed soil property data extracted from the literature. The landslide output was then substituted into a two-layer numerical model based on a shallow-water equation to simulate tsunami propagation. The results were combined with the other tsunami sources, i.e., earthquakes and observed coastal collapses, and validated with various postevent field observational data, including tsunami runup heights and flow depths around the bay, the inundation area around Palu city, waveforms recorded by the Pantoloan tide gauge, and video-inferred waveforms. The model generated several submarine landslides, with lengths of 0.2–2.0 km throughout Palu Bay. The results confirmed the existence of submarine landslide sources in the southern part of the bay and showed agreement with the observed tsunami data, including runups and flow depths. Furthermore, the simulated landslides also reproduced the video-inferred waveforms in 3 out of 6 locations. Although these calculated submarine landslides still cannot fully explain some of the observed tsunami data, they emphasize the possible submarine landslide locations in southern Palu Bay that should be studied and surveyed in the future.

Highlights

  • Indonesia has recently experienced hardship because of earthquakes and tsunamis

  • 2.5 million people have been exposed to a tsunami with a 500 year return period, and a recent study suggested that Indonesia ranks third in the world for the 30 proportion of the population exposed to tsunamis (Løvholt et al, 2014)

  • 5 Conclusions Rather than employing a trial-and-error approach to the generation of hypothesized landslide sources, this study applied a 360 landslide model based on slope stability analysis for the first time to provide a better understanding of the potential submarine landslide-induced tsunami phenomenon

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Summary

Introduction

Indonesia has recently experienced hardship because of earthquakes and tsunamis. 2.5 million people have been exposed to a tsunami with a 500 year return period, and a recent study suggested that Indonesia ranks third in the world for the 30 proportion of the population exposed to tsunamis (Løvholt et al, 2014). A total of 9 tsunamis have been observed since 2000, 8 of which were associated with a significant earthquake, including the deadly Indian Ocean tsunami in 2004, according to the National Geophysical Data Center/World Data Service (NGDC/WDS, 2021). These types of natural disasters have caused many economic losses and fatalities in Indonesia. Horspool et al (2014) indicated that the annual probability of experiencing a tsunami similar to the 35 aforementioned 3.0 m tsunami is ~0.1-10% across the entire Indonesian coast

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