[S-CG52] Inter-segment Tectonics: Interdisciplinary Research on Responses to Plate Subduction

[SCG52-P08] Sesimic Velocity Structure Beneath Sulawesi Island, Indonesia

*Ahmad Mustafid Miftahul Huda^1,2,3,4、Hsin-Hua Huang^2,3、Yih-Min Wu^2,3、Dimas Salomo J. Sianipar^5,6、Emi Ulfiana^6,7,8 (1.Taiwan International Graduate Program (TIGP) – Earth System Science Program (ESS), Academia Sinica and National Taiwan University (NTU), Academia Sinica, Taipei 11529, Taiwan、2.Department of Geoscience, National Taiwan University、3.Institute of Earth Science (IES), Academia Sinica、4.Sekolah Tinggi Teknologi Migas Balikpapan (STT MIGAS), Indonesia、5.State College of Meteorology, Climatology, and Geophysics (STMKG), Indonesia、6.Indonesian Agency for Meteorological, Climatological and Geophysics (BMKG)、7.Taiwan International Graduate Program (TIGP) – Earth System Science Program (ESS), Academia Sinica and National Central University (NCU), Academia Sinica, Taipei 11529, Taiwan、8.Department of Earth Sciences, National Central University)

キーワード：earthquake relocation, North Sulawesi Trench, Sula slab, travel time tomography

Indonesia's Meteorology, Climatology, and Geophysical Agency (BMKG) has significantly expanded its seismic monitoring network, tripling the number of stations. This improvement allows for higher-resolution studies of Sulawesi’s tectonic structure, which is shaped by the interactions of the Philippine Sea Plate, the Eurasian Plate, and the Indo-Australian Plate. Sulawesi’s complex tectonic environment has led to major earthquakes, including the devastating 2018 event that triggered a tsunami and widespread liquefaction, emphasizing the need for better seismic models. Previous studies have attempted to determine the velocity structure of Sulawesi, but most of them used fewer stations than the current BMKG-enhanced seismic network and focused on either P-wave (Vp) or S-wave (Vs) velocity models separately, limiting their effectiveness for earthquake relocation and structural imaging. This study aims to refine the velocity structure of Sulawesi by utilizing the increased density of seismic stations and earthquake data. A new 1-D velocity model was developed using data from 1,788 earthquake events, incorporating 17,365 P-wave readings and 6,787 S-wave readings. Statistical analysis of earthquake locations indicates that this updated velocity model can be reliably applied to routine seismic monitoring. We then used this refined 1-D model as the initial model for a 3-D travel-time tomography inversion, incorporating data from 10,177 earthquake events and a total of 166,974 P- and S-wave readings. The resulting 3-D tomography model provides a detailed representation of the Vp, Vs, and Vp/Vs structures beneath Sulawesi. Several significant features were identified, including a negative velocity anomaly beneath the northern arm of the Sulawesi volcanic arc, indicating a potential magmatic source. Additionally, we observe fast velocity anomalies near the North Sulawesi Trench, depicting the southward subduction of the Celebes Sea Plate and the northward subduction of the Sula slab. The model also reveals notable crustal thickness variations in western Sulawesi, part of the Sunda Continent, and a sharp slow-velocity anomaly beneath the island arc. The improved velocity model enhances our understanding of Sulawesi’s tectonic structures and lays a foundation for future seismic hazard assessments in the region.