SEISMICITY STUDY OF EASTERN PART OF INDONESIA AND TOMOGRAPHIC IMAGING BENEATH SUNDA-BANDA ARC TRANSITION ZONE

• Main Author: Supendi, Pepen
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/70971
• Institution: Institut Teknologi Bandung

Eastern Indonesia lies within a highly complex tectonic region resulting from the collision of the Australian and Sunda blocks, and the interaction of the Pacific and Philippine Sea plates. The aims of this study to analyze of seismicity in the eastern part of Indonesia based on the earthquake hypocenter relocation using a 3-D seismic velocity model, especially for the Lombok, Palu and Mamasa earthquakes in 2018; to find out the P-wave velocity structure in the Sunda-Banda Arc Transition Zone (SBATZ) based on the travel time tomography that can explain the tectonic process in the area related to differences in the chemical composition of active volcanoes in ZTBSB compared to Sunda arc. The earthquake relocations were performed using a teleseismic double-difference method, the arrival times data for P-and S-waves from local, regional, and teleseismic stations were taken from the Agency for Meteorology, Climatology, and Geophysics of Indonesia (BMKG) and the International Seismological Centre (ISC) for the time period of April 2009 to November 2018. The relocated catalog provides an improved view of seismicity in eastern Indonesia over the study period, sharpening locations and interpretations of seismogenic features throughout the Sunda-Banda arc transition zone, the Banda arc, the Molucca Collision Zone, Sulawesi, and Papua. The relocated aftershocks show that the destructive Mw 7.0 and Mw 6.9 earthquakes of the Lombok sequence ruptured two different regions: The Mw 7.0 earthquake propagated westward, whereas the Mw 6.9 earthquake propagated eastward. The entire sequence of Lombok earthquakes was most likely started by the Mw 6.4 event as the initial event or foreshock, which then triggered fold-thrust belt on both sides. The Mw 7.5 Palu earthquake occurred along the Palu-Koro Fault, filling a seismic gap that had not ruptured in an Mw 6.0 event or larger since at least 1900. The distribution of aftershocks indicates that the northern part of the Palu-Koro Fault has lower relative seismicity rates than the southern part at shallow depths, and that off fault aftershocks are mostly located to the east of the Palu-Koro Fault. About 30 days after Palu earthquake, there have been 535 of swarm earthquakes in the Mamasa (West Sulawesi), the seismicity pattern and focal mechanism show these earthquakes probably have been caused by normal faults along ~ 50 km from north to south with a dipping at a ~45° angle to the east. For the Sunda-Banda arc transition zone also used a waveform from 30 YS temporal seismic stations in 2014- 2016 taken from the IRIS Data Management Center, 576 hypocentres were determined using Hypoellipse, then 415 were relocated using HypoDD. A new 3-D seismic P-wave velocity model in the area from local earthquake tomography reveals: Northward subduction of oceanic lithosphere, associated with the convergence of Australia and Sundaland, as a high velocity zone extending down iv to ~200 km depth; Two distinct low velocity zones, one immediately above the slab, which is likely a zone of partial melt, and one in the 0-40 km depth range, which is probably a magma chamber associated with active volcanoes above; A northerly dipping high velocity zone that bisects the two low velocity anomalies, which we interpret as a continental microplate which caused the magma supply is contaminated by interaction with this continental material as it ascends from the melt region below.