Overview of long-distance flow-slide caused by the 2018 Sulawesi earthquake, Indonesia

Abstract On 28th September 2018, an earthquake of Mw 7.5 struck Donggala Regency, Central Sulawesi, Indonesia, resulting in a catastrophic disaster and a large numbers of casualties. In this report, the results of the preliminary field investigations carried out by the authors’ team are summarized. The earthquake caused four major long-distance flow-slides on very gentle slopes of approximately 1–5% in and around Palu City: Balaroa, Petobo, Jono Oge and Sibalaya. The maximum flow distance at each site was several hundred meters or more. Spring waters were found in all affected areas even though there had not been a lot of rainfall before the survey. Interviews with local residents and witnesses of the flow-slide provided much evidence that the shallow groundwater in the affected areas had been pressurized before the earthquake. This confined groundwater is thought to have played an important role in the occurrence of long-distance flow-slide. In addition, the thickness of the flowed ground was found to be about 1.5 m by pit excavation survey in Jono Oge. Based on the results of the field survey and provided evidence, the likely fundamental mechanisms of the flow-slide are discussed.