Coastal Subsidence Induced Several Tsunamis During the 2018 Sulawesi Earthquake

Abstract

The height of the tsunami caused by the Sulawesi earthquake in 2018 was higher than that estimated from the magnitude of the earthquake, and its cause is not well understood. Although it is conceivable that tsunamis originated from landslides in several cases, it is not known whether landslides were occurring in the coastal area at the time. This report describes the results of a field survey conducted to investigate the traces of subsidence and the characteristics of the tsunami incidents in the bay far from the epicenter. Subsidence was observed at a minimum of seven points along the coast; in accord with the reports of eyewitnesses, this suggests that subsidence might have generated tsunamis.

Source Model for the Tsunami Inside Palu Bay Following the 2018 Palu Earthquake, Indonesia

“…Field surveys following the recent Palu earthquake were conducted by Indonesian and international teams to measure tsunami heights, impacts, and collect eyewitness accounts (BMKG, 2018;Arikawa et al, 2018;Cipta et al, 2018;Muhari et al, 2018;Omira et al, 2019;Paulik et al, 2019). The tsunami was also recorded by a tide gauge station at Pantoloan harbor located inside Palu Bay.…”

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).…”

Subaqueous mass movements in the context of observations of contemporary slope failure

“…generation, supported by video observations of localised wave generation and evidence for coastal failures (Arikawa et al, 2018;Carvajal et al, 2019). While it is clear from the extraordinary video footage collected at the time that delta collapse and coastal landslides caused tsunamis (Figure 1), the role that subaqueous slope failures played in the main wave generation remains speculative, and no more conclusive than for comparative previous events where earthquake mechanisms could not clearly be reconciled with tsunami generation (e.g.…”