Analytical Study on Ground Behavior During the 2018 Sulawesi Earthquake, Indonesia

Abstract

The 2018 Sulawesi earthquake, Indonesia, caused long-distance ground flow in several areas in Palu city, about 80 km south of the epicenter, with the largest area reaching about 3.5 km × 1.5 km. The common feature of the long-distance ground flow area is that the slope of the ground surface is gentle. In this study, we aim to clarify the mechanism of the long-distance ground flow by using seismic response analysis and simplified liquefaction analysis. Three sites with different damage conditions will be targeted. Then, a one-dimensional soil column model is created from the boring log, and the response characteristics are analyzed by seismic response analysis. Also, a geological survey of the site confirmed that there are mountains of 2000 m in height around the site, thus water easily accumulates in the alluvial fan under the mountains. It is also assumed that pressurized groundwater exists. There are some possible causes of the flow: one is the formation of an aquifer beneath the surface layer, which may have initiated the flow; the other is the liquefaction from the surface layer to the cap layer, which may have caused the cap to come off and pressurized groundwater to be ejected, leading to long-distance ground flow. In this study, we consider the liquefaction of the surface layer, and the large relative displacement between the cap layer and the layer below it created water paths, and the pressurized groundwater is supplied continuously to the upper layer through the water paths. As a result, in terms of ground seismic response analysis results, shear strain and relative displacement were larger at the damaged point, but no remarkable results were obtained. However, in the simple liquefaction analysis, it was suggested that the liquefaction layer increased when the pressure is taken into account, leading to long-distance ground flow.