Imaging Complex Tectonic Structures and Slab Interactions beneath Sulawesi Island, Indonesia, from Enhanced Three-Dimensional Vp, Vs, and Vp/Vs Tomographic Models

The tectonic complexity of Sulawesi reflects one of the most intricate subduction systems in Southeast Asia. Subduction beneath northern Sulawesi controls both regional seismicity and volcanism. Although earthquake distributions delineate vertical subduction profiles, their geometries remain poorly resolved in subsurface imaging. The high density of earthquakes and improved seismic coverage across Sulawesi enable refined tomographic imaging of these structures. Subduction-related processes such as partial melting, indicative of magma generation, can also be characterized through seismic velocity anomalies. We inverted approximately 300,000 P- and S-wave arrival times recorded by 144 stations to resolve the geometry of northward subduction beneath northern Sulawesi. The tomographic model also suggests a possible origin of the Colo/Una-Una volcano beneath the Gorontalo Bay, possibly related to southward subduction. Although sparse seismicity in the northern region limits the resolution of southward subduction, vertical structures are resolved with improved clarity and continuity. These results refine previous tectonic interpretations of the Sulawesi region, providing new constraints on subduction geometry and its relation to volcanic processes. The improved velocity model can enhance regional earthquake monitoring and support future assessments of seismic hazards.