Mapping of Rock Vulnerability in Rantepao City, Indonesia for Disaster Mitigation Based on Microtremor Data

Rantepao City is the capital of North Toraja Regency. In recent years, the development in this city has been quite rapid; many high-rise buildings have begun to be built in both form of residential and office. Based on the 2019 Map of Indonesia's Disbursement Vulnerability Zone, Rantepao City is in a moderate liquefaction zone. Therefore, it is considered necessary to conduct research to map Rock Vulnerability using Microtremor data. This research is quantitative. Measurements are taken at 13 points with a duration of 45 minutes. The tools needed in data collection are a set of microtremors to record microwaves, and GPS to find out the coordinates of the measurement points. From the results of microtremor measurements in the city of Rantepao, each region has variable frquency values (F0) ranging from 0.470853 to 14.6016, amplification values (A0) values ranging from 2.86703 to 8.39741 and a susceptibility index (Kg) values ranging from 1.146179 to 24.87313. This indicates that the constituent rocks vary from hard to soft alluvial deposits. The lower the F0, the thicker the sediment layer is above the bedrock. Hard alluvial deposits tend to have a lower amplification factor compared to soft alluvial deposits. Based on the amplification factor, the hard alluvial deposits have lower values compared to soft alluvial deposits. With this map, it is hoped that the community can find out the condition of the rocks where they live and become a reference for the government in regional development planning.