ACTIVE FAULT STUDY IN SOUTHERN GARUT, WEST JAVA, BASED ON MAGNETOTELLURIC AND GRAVITY METHODS

• Main Author: Arisbaya, Ilham
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/78921
• Institution: Institut Teknologi Bandung

Inland active fault-related earthquakes often cause severe damage due to their proximity to the center of human activities. In recent years, dozens of shallow lowmagnitude earthquakes were felt in southern Garut, West Java, three of them were reported destructive. These earthquakes are interpreted to be related to an active fault, the Garsela Fault. Information regarding the Garsela Fault is still very limited, the interpretation was solely based on the seismicity lineament and analysis of the focal mechanisms of the 2016 and 2017 earthquakes. This study combines three dimensional (3D) gravity inversion modeling with two dimensional (2D) magnetotelluric (MT) inversion to study the subsurface. In general, gravity and MT modeling results are well correlated with one another and consistent with surface geological information. The gravity and MT modeling results show the lineament of the basement high blocks trending northeastsouthwest, forming the Kiamis High. The basement high block was originally a regional strike-slip fault, which later became a pathway for magma to rise and form a lineament of volcanic bodies that cut the Garut Basin. The heat from cooling magmatic intrusion may decrease the effective fault-normal stress of the rocks, leading to a decrease in fault failure resistance and may initiate rupture. This study supports the interpretation suggesting that the pore fluid’s pressure/temperature (PT) gradient contributes to earthquake initiation and propagation. The mechanism for shallow earthquakes in the southern Garut area is explained as a result of the interaction of tectonic deformation with magmatic activity. The surface geology, dominated by young volcanic products, must be a concern since it may amplify ground motion during an earthquake and inflict more extensive damage.