High-Resolution 3D Crustal Shear Wave Velocity Structure beneath Sulawesi, Indonesia, through Joint Inversion of Ambient-Noise Rayleigh-Wave Group and Phase Velocities

Sulawesi is situated at the triple junction of the Eurasian, Australian, and Pacific plates, where subduction, continental collision, strike-slip faulting, and extension have produced one of the most tectonically complex regions in Southeast Asia. To improve constraints on crustal deformation, tectonic evolution, and seismic hazards, we present a new high-resolution three-dimensional (3D) crustal shear-wave velocity (Vs) model of Sulawesi derived from ambient noise tomography. One year of continuous vertical-component recordings from 73 seismic stations was cross-correlated to retrieve Rayleigh wave empirical Green’s functions. Group- and phase-velocity dispersion curves were measured using frequency-time analysis and jointly inverted in a one-step inversion method to image the crustal Vs structure beneath Sulawesi. The resulting model shows sharp velocity contrasts across major faults, including the Palu-Koro and Matano faults, suggesting complex subsurface geometries rather than simple vertical structures, while the shallow velocity patterns may indicate structural linkages with the Lawanopo fault systems. High Vs zones are associated with metamorphic complexes, including Mekongga Metamorphic Complex, whereas low Vs regions are associated with volcanic regions in the northeastern Sulawesi and sedimentary basins, including Karama, Lariang, and Sengkang basins. While the origin of the Mamasa swarm remains debated, its location beneath a pronounced velocity contrast suggests possible local fault reactivation. In contrast, the 2019 Tolo Bay earthquake sequence coincides with a pronounced velocity contrast that may reflect crustal heterogeneity associated with the Banggai-Sula collision. These results provide new constraints on the crustal structure of Sulawesi and regional seismic hazard assessment.