TOMOGRAPHIC IMAGING OF P-WAVE VELOCITY STRUCTURE BENEATH SULAWESI USING FAST MARCHING TOMOGRAPHY METHOD

• Main Author: Lestari, Harmita
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/67176
• Institution: Institut Teknologi Bandung

Sulawesi lies within one of the highly complex tectonic region in Indonesia, this causes high earthquake activity in Sulawesi. High seismicity in Sulawesi is mostly caused by subduction in North Sulawesi and the Subduction of the Maluku Sea Plate as well as several active faults such as the Palu-Koro Fault, Matano Fault, Lawanopo Fault, Gorontalo Fault, and several other active faults in East Arm of Sulawesi. The aims of this research are to investigate seismicity based on earthquake hypocenter relocation and to establish the structure of the P wave velocity beneath Sulawesi using seismic tomography. The arrival time of the P wave and hypocenter characteristics were obtained from the Agency for Meteorology, Climatology, and Geophysics of Indonesia (BMKG) earthquake database from January 2017 to January 2021. The earthquake relocation were performed using a teleseismic double-difference (teletomoDD) method which is the development of double-difference method. The tomographic inversion process were performed using FMTOMO package to find out a more detailed P wave structure beneath study area. The hypocenter relocation findings demonstrate numerous seismicity patterns in active faults and subduction zones in Sulawesi. Seismicity in the South Arm (Central and West Sulawesi) is primarily driven by the Palu Koro Fault, as evidenced by the transfer of the hypocenter to the fault region. The Mamuju Fault and the Makassar Strait thrust are the primary causes of seismicity in West Sulawesi. Meanwhile, seismicity in the Southeast Arm and East Arm of Sulawesi is driven by Matano Fault activity and Maluku Sea Plate subduction on the East Arm of Sulawesi. Due to the activity of the Sulawesi Sea Subduction, high seismicity was also reported in the North Arm of Sulawesi, namely in Tomini Bay. The hypocenter relocation findings are utilised to evaluate the checkerboard resolution, which uses alternating negative and positive velocity anomalies as input in the forward modelling process to recover the input model till a depth of 80 km. The inversion tomography results demonstrate a contrast anomaly in the P wave velocity structure, particularly in places with complicated tectonic processes. Sulawesi Sea subduction and Sula subduction are depicted as positive P wave velocity anomalies. Meanwhile, the active fault area exhibits a contrasting P wave velocity anomaly,v with strong seismicity concentrated in the negative P wave velocity anomaly zone, which is most likely connected with a weak zone underneath the active fault.