LIQUEFACTION POTENTIAL EVALUATION IN TOBA CRATER INDONESIA

Abstract

Lake Toba Crater, specifically Samosir Island, Indonesia, is a caldera formed by the supervolcano eruption of Mount Toba. Furthermore, the region is susceptible to active earthquakes due to the presence of the Sumatran fault. Along the coastline, the soil is predominantly sandy, with a high groundwater level. These factors, namely earthquake and soil conditions, are reported to be the major triggering factors for a phenomenon known as liquefaction. According to the Indonesian Liquefaction Vulnerability Zone, Samosir Island is situated in a vulnerable area with medium potential. Therefore, this study aims to evaluate the liquefaction potential in Lake Toba Crater by taking a study case in the Culinary Building. Due to the SF site class of the study location, Site-Specific Response Analysis (SSRA) was required based on the Indonesian National Standard. A non-linear SSRA was used to determine the seismic wave propagation with DEEPSOIL v7. The analysis considered an earthquake exceedance probability of 2% in 50 years. The input parameters for the ground motion were obtained from the modification of 12 pairs of recorded data. The Peak Ground Acceleration value for each depth was generated from SSRA and used for liquefaction potential evaluation. This study used empirical methods, as well as two scenarios, namely maximum and frequent earthquakes with magnitudes of 6.4 Mw and 5.6 Mw, respectively. Based on the results, the area had liquefaction potential at 6-20 meters below the surface. The vulnerability level, as assessed using LPI value, was found to be very high, ranging from 25.71 to 56.51.