3-D SEISMIC VELOCITY TOMOGRAPHY IN BALI AND NUSA TENGGARA REGIONS BY APPLYING FAST MARCHING METHOD USING BMKG SEIMOGRAPH NETWORK

• Main Author: Rachmadi Priyambada, Fajar
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69834
• Institution: Institut Teknologi Bandung

Bali and Nusa Tenggara have high seismicity due to their location along the transition zone between the Indo-Australian subduction in the Sunda arc to the collision of the Australian continent in the Banda arc. Furthermore, there are the Flores Backarc Thrust and Wetar Thrust to the north of this area, both of which caused major earthquakes in the past, including the Flores earthquake and tsunami in 1992 and the Lombok earthquake in 2018. The purpose of this study is to determine the body wave velocity (Vp, Vs, and Vp/Vs ratio) beneath the Bali and Nusa Tenggara regions. We used 4,587 earthquake data catalogs from the Agency for Meteorology, Climatology, and Geophysics (BMKG) between 2019 and 2020 at coordinates 1120 E – 1280 E and 40 S – 130 S. We obtained 50,857 P- and 16,797 S-wave phases by re-picking of 4,587 events from 90 BMKG stations. To determine the hypocenter locations, we used the Non-Linear method, while the tomographic inversion used the fast marching method through the FMTOMO program. The results indicate several tectonic features in the study area, including the Indo- Australian slab and Flores Backarc Thrust, which have high Vp anomalies, high Vs anomalies, and low Vp/Vs ratio values. The angle of subduction of the Indo- Australian plate in this area is between 100 and 300. Flores Backarc Thrust has been identified by high Vp anomaly, high Vs anomaly, and low Vp/Vs ratio in the northern part of Flores, which extends from the northern island of Flores to the northern of Bali at a depth of about 4 km to 50 km. The east side of Sumba Island, Savu Island, and Rote Island in the western part of Timor has high Vp, high Vs, and low Vp/Vs ratios. Within the study area, volcanic zones exhibit low Vp, low Vs, and high Vp/Vs ratios at a depth of 25 km.