Consideration of submarine landslide induced by 2018 Sulawesi earthquake and tsunami within Palu Bay

Abstract

On September 28 2018, an Mw 7.5 strike-slip earthquake occurred to the north of Palu Bay on the Sulawesi Island, Indonesia. This triggered a destructive tsunami within the bay, which reached Palu city. Simulation have been conducted to investigate the landslide source. However, the tsunami should be investigated considering a physical model in the area where detailed bathymetric survey had not been conducted. In this study, we investigated the impact of coastal landslides on the southern part of the bay using a two-layer model. Owing to the increasing collapse volume, the southern west coastal landslide could approximately explain the observations in Palu city. However, the calculated mass volume of the source largely overestimated the bathymetric survey data. Hence, we considered the possibility of submarine landslide in the southern part of the bay and the simulation results could approximately explain the maximum tsunami heights in the southern part of the bay. These results suggest that more detailed multibeam data will be required to investigate the possible submarine landslide in the southern area which could induce a destructive tsunami reaching Palu city within a few minutes after the collapse.

Back-projection results for the Mw7.5, 28 September 2018 Palu earthquake-tsunami

“…3), the front of high-frequency radiations bringing energetic seismic waves arrives at the inlet and in turn enters the bay. This finding seems to be in good agreement with the predicted locations of submarine landslides, which is just outside and within the bay to form the double sources of tsunamis [1,3,4,5]. This, along with multiple wave reflection within the bay owing to its geometry, could be the answer to the question of why such an event generated unexpectedly high tsunami waves, where the western shores of the bay are mostly affected by the tsunamis [6,7].…”

“…3 is that different sizes of the gradation blue circles indicate varying amplitudes hence the corresponding energies measured along the western side of the bay from the entrance to Palu. We speculate on the cause of this finding in the current study by corresponding it to a non-seismic source of submarine landslides that most likely occur at some possible locations just outside and within the bay [1,3,4,5,7]. In turn, the double sources of seismic and non-seismic origin combined with multiple reflection of tsunami waves within the relatively narrow geometry of the bay have resulted in unexpected tsunami measures in terms of higher run-up and larger inundation than those usually observed in tsunamis generated by a strike-slip earthquake [8].…”

“…A series of destructive tsunami waves struck the coastlines of Palu Bay on 28 September 2018 following a strike-slip earthquake of Mw 7.5 with the epicentre was found at about 75-80 km to the north of Palu, a densely populated city in Central Sulawesi, Indonesia [1,2]. Some studies [3,4,5] have argued for the likely most possible submarine landslide for the source. Other publications [6,7,8] have reported the unexpected tsunami inundation and height found in coastal regions along the bay from field surveys.…”

Tsunami Effects on the Coast of Mexico by the Hunga Tonga-Hunga Ha’apai Volcano Eruption, Tonga

“…However, massive explosions by volcanoes can trigger other hazards such as tsunamis. Tsunamis triggered by volcanic eruptions are generated by submarine landslides and caldera collapses (e.g., Maeno & Imamura, 2011 ; Nagai et al, 2021 ; Nomanbhoy & Satake, 1995 ; Pararas-Carayannis, 1992 ), and by coupled ocean and atmospheric shock waves during explosions (Bryant, 2001 ; Pelinovzky et al, 2005 ; Simkin & Fiske, 1983 ; Choi, 2003 ; Yokoyama, 1981 ). To generate coupled sea-atmospheric waves, volcanic eruptions must be large, e.g., the 1883 Krakatau eruption (Yokoyama, 1981 ).…”

Tsunami effects on the Coast of Mexico by the Hunga Tonga-Hunga Ha’apai volcano eruption, Tonga

“…Tsunamis triggered by volcanic eruptions are generated by submarine landslides and caldera collapses (e.g. Nagai et al, 2021;Maeno and Imamura, 2011;Nomanbhoy and Satake, 1995;Pararas-Carayannis, 1992), and by coupled ocean and atmospheric shock waves during explosions (Bryant, 2001;Pelinovzky et al, 2005;Simkin and Fiske, 1983;Choi, 2003;Yokoyama, 1981). To generate coupled sea-atmospheric waves, volcanic eruptions must be large, e.g.…”