FOCAL MECHANISM STUDY IN WEST JAVA AND THE SURROUNDING

• Main Author: ROSYADI (NIM: 10211042), FACHNI
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/22014
• Institution: Institut Teknologi Bandung

Indonesia is the path of the confluence of three major plates, namely Indo-Australian plate that moves northward relatively, the Eurasian plate that moves southward relatively, and the Pacific plate that move westward relatively. The plates meeting led to frequent earthquake due to collision or shifting of plates. Focal mechanism is the depiction of inelastic deformation in the area of earthquake sources that generates seismic waves. The problems in this thesis is determining the type and direction of the fault that causes earthquakes in West Java and the surrounding. The steps are determining the required seismic recording station. Each seismic station records a first movement pattern of P wave. Then, symbolizing the station by the black dots to the up first motion, white dots to the down first motion, and cross sign to the undetermined first motion. Then, connecting the cross signs by lines to form multiple quadrants that each quadrant has a similar symbol. Each quadrant is colored according to the same type of symbols so that forms a kind of focal mechanism. The purpose of this study is to determine the focal mechanism and seismic moment tensor of the earthquakes around Lembang, Bandung, West Java, and also to determine the direction of the movement of the fault. The methods used are focal mechanism solutions and moment tensor solutions. The earthquakes used in this study are the earthquakes that occur in West Java and the surrounding. Focal mechanism of the earthquake located around Lembang, Bandung, West Java is reverse (thrust) fault and the fault moved from south to north and the moment tensor is 4.523×1017 Nm. Focal mechanism of the earthquake located around Cilengkrang, West Java is oblique-reverse fault and the fault moved from SSW to NNE and the moment tensor is 2.349×1017 Nm. Focal mechanism of earthquake located 168 km SSW of Cicadas, Indonesia is strike-slip fault and the faults moved counterclockwise and the moment tensor is 5.691×1017 Nm.