Preliminary Field Study of the Petobo Flow Slide After the 2018 Indonesia Palu Liquefaction

A huge flow slide induced by liquefaction occurred in several areas of Palu city, Indonesia, due to the Mw 7.5 Palu-Donggala earthquake on Friday, 28 Sept 2018. Many villages, including Balaroa, Petobo, Jono Ogee, and South Sibalaya, had experienced catastrophic destructions due to flow slide liquefaction. This study focused on the flow slide area of Petobo. Surface observations and Electrical Resistivity Imaging (ERI) were conducted in the Petobo area. Based on surface observations, the flow slide area can be divided into four possible morphological zones, which include Ground Slide (GS), Lateral Spread (LS), Liquefaction Flow (LF), and Debris Flood (DF). The results of ERI show that in the GS zone near the Gumbasa canal, soil materials are dominated by sandy gravels or gravelly sands. Furthermore, GS and LS zones are covered mainly by dry sand and gravel. Interbedded saturated sands and gravel were found at the top layer of the LF zone. Lastly, the DF zone subsurface is generally composed of silt or clay, interbedded with sand in a saturated condition.