The 2018 Sulawesi tsunami in Palu city as a result of several landslides and coseismic tsunamis

ABSTRACT

The September 28 2018 Palu tsunami surprised the scientific community, as neither the earthquake magnitude nor its strike-slip mechanism were deemed capable of producing the wave heights that were observed. However, recent research has shown that the earthquake generated several landslides inside Palu bay. The authors conducted a post-disaster field survey of the area affected to collect spatial data on tsunami inundation heights, nearshore and bay bathymetry, and carried out eyewitness interviews to collect testimonies of the event. In addition, numerical simulations of the tsunami generation and propagation mechanisms were carried out and validated with the inferred time series. Seven small submarine landslides were identified along the western shore of the bay, and one large one was reported on the eastern shore of Palu City. Most of these landslides occurred at river mouths and reclamation areas, where soft submarine sediments had accumulated. The numerical simulations support a scenario in which the tsunami waves that arrived at Palu city 4–10 min after the earthquake were caused by the co-seismic seafloor deformation, possibly coupled with secondary waves generated from several submarine landslides. These findings suggest that more comprehensive methodologies and tools need to be used when assessing probabilistic tsunami hazards in narrow bays.

KEYWORDS:

• Palu city
• landslide tsunami
• numerical simulation

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Acknowledgements

The field survey was financially supported by Penta Ocean Co. Ltd. and by New CC Construction Consultants Co., Ltd. Part of the present work was performed as a part of the activities of Research Institute of Sustainable Future Society, Waseda Research Institute for Science and Engineering, Waseda University. The authors would like to thank ANID (Chile) for its FONDAP 15110017 grant, and the Postgraduate program of Universidad Catolica de la Santisima Concepción for its support. This research was also partially funded by the Japan Society for the Promotion of Science (JSPS KAKENHI 16KK0121, JP19K15104,16J00298 and 19J00814). The authors also thank Dr. Valkaniotis Sotiris for sharing bathymetry data, Dr. Yoshiki Yamazaki for guidance on the application of kinematic tsunami initial condition as well as horizontal deformation, and the two anonymous reviewers.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

¹ https://en.wikipedia.org/wiki/2018_Sulawesi_earthquake_and_tsunami

² https://www.dji.com/phantom-4-pro

³ https://www.paraview.org/

Additional information

Funding

This work was supported by the Japan Society for the Promotion of Science [19K15104]; Japan Society for the Promotion of Science [16KK0121]; Japan Society for the Promotion of Science [19J00814]; Japan Society for the Promotion of Science [16J00298]; ANID/FONDAP [15110017].