3D SEISMIC WAVE VELOCITY STRUCTURE IMAGING USING DOUBLE-DIFFERENCE TOMOGRAPHY METHOD IN LOMBOK AREA

• Main Author: Rohim, Kasbillah
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/82547
• Institution: Institut Teknologi Bandung

Tectonic activity on Lombok Island is quite complex, seismicity in the area is quite active and many earthquakes with significant intensity. A deeper understanding of the tectonic processes on Lombok Island is important to anticipate potential earthquake hazards. Seismic wave tomography methods are applied to help understand tectonic characteristics and image subsurface structures. In this study, the author uses the double-difference tomography method to image the subsurface structure using wave arrival time data from a series of earthquake events. This study uses earthquake catalogue data obtained from a local seismograph network recorded by 20 receiving stations from the Bandung Institute of Technology, Earth Observatory of Singapore (Nanyang Technological University), and the Centre for Volcanology and Geological Disaster Mitigation from 4 August to 9 September 2018, with a total of 3,259 events with a P-wave phase of 28.728 and an S-wave phase of 20.713. The tomographic inversion used in the doubledifference algorithm is the damped LSQR method. The interpreted tomogram is an area with good resolution test results. The resolution test method in this research is derivative weigh sum (DWS) and checkerboard test. The results of the inversion of P and S wave velocity tomography with the double-difference method can image the condition of the features that exist in the subsurface of Lombok Island. The velocity structure in the fault zone can be indicated by low P-wave velocity anomalies, low S-wave velocity anomalies, and high Vp/Vs ratio values ranging from 1.8 to 2. At a depth of about 0-10 km with the formation extending from west to east along the north coast of Lombok Island, it is indicated as a segmented fault. At a depth of about 15-20 km east of the volcanic complex of Mount Rinjani is indicated as a compact and dry rock mass.