Liquefied gravity flow-induced tsunami: first evidence and comparison from the 2018 Indonesia Sulawesi earthquake and tsunami disasters

Abstract

On 28 September 2018, a strong earthquake with a moment magnitude of 7.5 occurred on the island of Sulawesi, Indonesia. This earthquake caused extensive liquefaction and liquefaction-induced flow slides inland. Despite a strike-slip fault, which typically displaces land horizontally, being unlikely to produce significant tsunamis, the earthquake in fact caused devastating tsunamis. Our field investigations showed that there was an occurrence of extensive liquefaction in coastal areas. Significant coastal liquefaction can result in a gravity flow of liquefied soil mass that can cause a tsunami. A comparison with a past disaster of the strike-slip fault Haiti earthquake tsunami indicated that essentially the same occurred at the Palu coast of Central Sulawesi. Namely, liquefaction-induced total collapse of coastal land caused liquefied sediment flows, resulting in a tsunami. An important difference between this time and Haiti was that such total collapses and flows of coastal land due to liquefaction occurred at several (at least nine) places, resulting in multiple tsunamis. Analysis of the tidal data implied that less than 20% of the tsunami height was related to tectonic processes, and the majority was caused by the coastal and submarine landslides as characterized by liquefied gravity flows.

Earthquake Education Through the Use of Documentary Movies

“…The earthquake shaking together with the deadly tsunami waves resulted in extensive damage to life and property with a loss of more than 2,000 lives. Importantly, the earthquake ruptured a previously mapped active left-lateral strike-slip fault system, the Palu-Koro fault (Figure 2B), at a shallower depth of 10.0 km (Hui et al, 2018;Sassa and Takagawa, 2018). The unfortunate loss of life and property is mainly related to tsunami, liquefaction, and earthquake shaking, which clearly suggests that poor infrastructure and lack of earthquake disaster preparedness are the unpleasant realities that continue to challenge us.…”

Submarine landslide source models consistent with multiple tsunami records of the 2018 Palu tsunami, Sulawesi, Indonesia

“…Figure 1a shows coastal tsunami flow depths and run-up heights reported by those surveys. Coastal collapses at multiple locations were also reported (International Tsunami Survey Team (ITST) 2018; Arikawa et al 2018;Sassa and Takagawa 2019). Seafloor bathymetric surveys after the earthquake were also conducted (Frederik et al 2019;Takagi et al 2019).…”

Modeling the Sources of the 2018 Palu, Indonesia, Tsunami Using Videos From Social Media

“…At the tide gauge station in Pantoloan, the tide records in the hours before and after the tsunami show that the mean sea level did not change as a result of the earthquake (see top right panel of Figure ), eliminating the possibility of a large amount of deep dip slip. Post‐tsunami surveys also have not shown evidence of significant permanent changes in relative sea level, except for areas of very localized coastal collapse likely linked to landslides (e.g., Muhari et al, ; Sassa & Takagawa, ).…”

“…They found evidence of a significant landslide with an area of 1 km , which may be related to the generation of tsunami waves, as reported by eye‐witnesses. Sassa and Takagawa () conducted a survey along the coast of the bay and found evidence of liquefaction‐induced coastal collapse and associated local subsidence that could have generated tsunami waves as a result of liquefied sediment flows. Carvajal et al () detected areas of coastal collapse and tsunamigenic potential by analyzing satellite imagery from Google Earth and by collecting social media videos from nearby locations showing the generation of tsunami waves.…”