Analysis of the Rock Layer Contact Using the Gravity Data of Satellite Imagery and Resistivity Method

Abstract

Research with the gravity data of satellite imagery and resistivity methods, Schlumberger configuration in the area of Sutami dam, and its surroundings has been undertaken. This study aims to determine the types of rock layer contact between limestone sediments and volcanic sediments for disaster mitigation. The Gravity data of satellite imagery was obtained from the Global Gravity Model Plus (GGMplus). The research area was 15 km x 15 km; the space between the points was 300 meters with 3000 measurement points. Resistivity data was obtained with an MAE type A6000E resistivity meter; the number of research points was 2 sounding points arranged in parallel to get 2D data. The location of data collection with the resistivity method, Schlumberger configuration was determined based on the results of research using gravity data of satellite imagery. Complete Bouguer anomaly values ranged from 73.6 mGal-89.3 mGal. The northern part of the research location has a lower Complete Bouguer anomaly than the southern area. It was because the northern part of the study area was part of volcanic sediment, although it was only on the surface, and the southern part was part of limestone sediment. Based on the value of resistivity data, the types of rock at research points 01 and 02 were soil, limestone, and sandy limestone. It was because the research point was located in a Campurdarat Formation. The results indicate that the contact layer between limestone and volcanic sedimentaries is located in: Campurdarat Formation, Wuni Formation, and the Butak Volcanic Product; Nampol Formation and Tuff Deposit; Tuff Deposit and Campurdarat Formation. This contact layer is more difficult to consolidate, so infrastructures built on it are more vulnerable.