MAGNETIC BASEMENT RELIEF ESTIMATION OF SUMANI AND SIANOK SEGMENT IN THE GREAT SUMATRAN FAULT

• Main Author: Amalia Hoja Pristyana, Velly
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/73678
• Institution: Institut Teknologi Bandung

The magnetic method is one of the geophysical methods used to delineate structures beneath the Earth's surface, one of which is the magnetic basement relief (MBR). Basement structure modeling has been developed due to its usefulness in the exploration of hydrocarbons and minerals. This structural modeling is usually carried out in sedimentary basin areas to detect the boundaries between the sediment layers and the magnetic basement to estimate the hydrocarbon potential in the studied area. The Sumani segment is a volcanic area with complex geological conditions dominated by many rock intrusive bodies that is part of the Sumatran Fault. MBR modeling in this area tends to be difficult because the susceptibility value contrasts of the constituent rocks are not high. Being part of the Ring of Fire complex, Indonesia hosts many volcanic areas. If MBR modeling can be successfully carried out in the Sumani Segment area, this will be the first step in implementing this method in Indonesia. Initially, the MBR modeling process was difficult to carry out. Several technologies, methods, and programs have been studied to ease the process of MBR modeling. Among those methods, there is the MagB_Inv program that was developed based on the iterative inversion method, and the Euler deconvolution method has also been used by several researchers to estimate the model of MBR. Both of those methods will be used in this research. The Euler deconvolution procedure was carried out three times using structural index (SI) values of 0, 1, and 2. Then, the results obtained from the modeling were analyzed based on the difference in the average depth and the relief pattern between the modeling results and the reference model obtained from previous studies. Based on the analysis of the results of all the methods used, the MagB_Inv program has limitations for modeling research areas with complex geological structures, so it is not suitable for modeling this research area. The limitation occurred due to the magnetization contrast parameters and average depth as the initial parameters for MagB_Inv modeling. The magnetization contrast parameter allows modeling to be carried out by assuming the study area is divided into two main layers consisting of the MBR layer and other rock layers above it, which causes lateral variations in the study area caused by the rocks not being imaged properly. For the average depth parameter, because only one value is used as the basis for the MBR modeling for the entire study5 area regardless of its size and geological complexity, the complex geological conditions cannot be properly represented. It happens because, in areas with complex geology, the contrast in basement depth values between one zone and another can be very different, so using one average depth value as the initial model for all regions is not appropriate. As for the Euler deconvolution method, of the three structural indices used, the most optimal results are obtained when using a value of 1. Of all the methods used in this study, the most suitable method to be applied to the Sumani Segment area is the Euler deconvolution method with SI = 1. Furthermore, for additional analysis, modeling was also carried out in the Sianok Segment area using MagB_Inv. The Sianok Segment area was chosen due to the presence of a thick tuff layer on the surface, which can represent a sedimentary basin area. The modeling results show conformity with the reference, proving that the MagB_Inv program can be utilized to model the MBR in the volcanic region if it is composed of thick tuff layers.