Understanding of Petobo liquefaction flowslide by 2018.09.28 Palu-Donggala Indonesia earthquake based on site reconnaissance

The Palu-Donggala earthquake struck Palu city of Sulawesi island, Indonesia, on 28 September 2018. A large-scale liquefaction phenomena occurred in some areas which caused massive fatalities and destructions. The most severe liquefaction incident during the earthquake followed by flowslides occurred in Petobo district of the city. The affected area due to Petobo flowslide liquefaction was approximately 1.64 km(2). The damages were severe because of densely populated area with estimated more than 3300 houses collapsed and nearly 2000 fatalities. The slide materials transformed into debris and flowed on the low-relief ground of about 2% with a slide distance of more than 800 m. A site reconnaissance of Petobo flowslide was conducted in early 2020, which covered surface observations and documentations before and after the flowslide, interpretations of geological characteristics, summary of witness interviews, analyses of ground displacement and changes in surface elevation and slope due to the flowslide. The results reveal insights as to the failure mechanism of the Petobo flowslide. Based on the observed phenomena on the surface, the Petobo flowslide area could generally be divided into four types of morphology, namely, ground slide (GS), liquefaction spread (LS), liquefaction flow (LF) and debris flood (DF). The GS and LS were considered to be the initiation zones, then the slide materials spread down and formed LF zone. In this area, the soils became wet and muddy as triggered by liquefaction. The liquefied materials then transported into DF zone where densely populated areas in lower elevation of the site were hit.

Automated summary

The Palu-Donggala earthquake in September 28, 2018, caused large-scale liquefaction phenomena in Palu city of Sulawesi island, Indonesia, resulting in massive fatalities and destructions, especially in the Petobo district where a significant flowslide liquefaction occurred.