Identification of Basement and Subsurface Structure of Depok City by Using Esa-Mwt Method on Gravity Data

Identification of Basement and Subsurface Structure of Depok City by Using ESA-MWT Method on Gravity Data

M. Syamsu Rosid1 and Renaldi Antoni H.1

1Replace this text with author’s affiliation (use full address)

The superscript * indicates the corresponding author’s email address

2Department of Physics, FMIPA Universitas Indonesia, Kampus UI Depok,
Depok 16424, Indonesia

*Corresponding author: syamsu.rosid@ui.ac.id

ABSTRACT

Basement is a hard layer which has a high-density contrast with the layer above it. 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 deepness 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 gr / cc which was obtained by using the Paresis 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 areas of the study area, where its fault identified as normal fault.

1. Introduction

Depok is a developing city adjacent to the capital city of Jakarta. This cause development and additional infrastructure are needed. As an effort in setting up the infrastructure, gravity survey was conducted to find out information about the condition of the basement. Knowledge of the basement information is something that needs to be considered in determining the construction location because it affects the resistance of subsurface rocks in supporting buildings.

     Gravity method is a method commonly used to investigate and identify the bodies of rock or structure of subsurface density variations associated with laterally [1]. But the gravity method is not sufficient to determine the depth of the basement, so it takes Energy Spectrum Analysis - Multi Window Test (ESA-MWT) method to determine the depth of the basement and Multi Scale - Second Vertical Derivative (MS-SVD) method to determine the location and type of fracture. Subsurface modelling was made as an interpretation of gravity data.