Identification of basement and subsurface structure of Depok City by using ESA-MWT gravity data

Abstract

Basement is a hard layer which has a high-density contrast compare to the above it layer. In geotechnics, this layer is useful for the basement installation of high-rise buildings and other heavy buildings. Rock density contrast is sensitive physical parameter to be detected using gravity data. The study conducted in Depok City is aimed to identify the presence and the depth of the basement. Gravity data has been collected from 87 stations throughout the city of Depok. The average density value of rocks in the study area is 1.73 g/cc which was obtained by using the Parasnis method. The shallow basement layer is mapped using the Energy Spectrum Analysis - Multi Window Test (ESA-MWT) method. This method works by windowing test points from Complete Bouger Anomaly (CBA) values to get the interface depth for each test point. The fault structure can be identified through a residual anomaly map and by the Multi Scale - Second Vertical Derivative (MS-SVD) method whose results correlate with each other. The basement layer was successfully identified among the 3 other horizon layers and was at a depth of 0 - 68 m below the subsurface. Fault structures were also identified in the study area in the North and South part of the study area, where its fault identified as a normal fault.