Preprints
https://doi.org/10.5194/nhess-2021-170
https://doi.org/10.5194/nhess-2021-170

  22 Jun 2021

22 Jun 2021

Review status: this preprint is currently under review for the journal NHESS.

Submarine Landslide Source Modeling using the 3D Slope Stability Analysis Method for the 2018 Palu-Sulawesi Tsunami

Chatuphorn Somphong1, Anawat Suppasri1, Kwanchai Pakoksung1, Tsuyoshi Nagasawa2, Yuya Narita2, Ryunosuke Tawatari2, Shohei Iwai2, Yukio Mabuchi2, Saneiki Fujita1, Shuji Moriguchi1, Kenjiro Terada1, Cipta Athanasius3, and Fumihiko Imamura1 Chatuphorn Somphong et al.
  • 1The International Research Institute for Disaster Science, Tohoku University, Miyagi, 9800845, Japan
  • 2Pacific Consultants Company Limited, Miyagi, 9800811, Japan
  • 3Center for Volcanology and Geological Hazard Mitigation, Geological Agency of Indonesia, Bundung, Indonesia

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.

Chatuphorn Somphong et al.

Status: open (until 14 Aug 2021)

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Chatuphorn Somphong et al.

Chatuphorn Somphong et al.

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Short summary
The majority of past research used assumed landslides to simulate tsunamis, but they were still unable to properly explain the observed data. In this study, submarine landslides were simulated for the first time using a slope-failure-theory-based numerical model. The findings were verified with post-event field observational data. They indicated the potential presence of submarine landslide sources in the bay's southern parts and were consistent with observational tsunami data.
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