An Overview Study of Flowslide Liquefaction in Petobo, Palu, Indonesia

Abstract

A magnitude (Mw) 7.5 Palu-Donggala earthquake struck Palu, Indonesia on Friday, 28 September 2018 at 18:02:44 Central Indonesia Time (GMT+8). The earthquake resulted in tsunami and flowslide liquefaction. Balaroa, Petobo, Jono Oge and South Sibalaya were affected areas of flowslide liquefaction. Area of Petobo flowslide liquefaction had the largest impact as compared to other locations. This paper emphasizes on the observations on the ground surface when liquefaction occurred in Petobo. Interviews with the survivors and living witnesses, displacement vectors with reference to buildings, observations of soil conditions and groundwater levels as well as descriptions of conditions pre- and post-slide, are conducted in these observations. In addition, several data consisting of Satellite Imagery, DEM (Digital Elevation Model), regional geology and some photographs taken at the site are also discussed. Results show the slope of the area of flowslide liquefaction ranges from 1° to 2°. Besides earthquake shaking, soil types and groundwater tables are believed to have had contributions to the flowslide liquefaction. Loose silty medium to fine sands are found in the flowslide areas. Based on interviews, witnesses indicated the liquefaction occurred in about few seconds after the initiation of shaking. The ground then became like muddy flow and buildings started to move or sink. After flowslide, large swampy areas had appeared and the soft ground took several weeks to become hardened again.