3-D Shear Wave Velocity (Vs) & Crustal Interface (Sediment Basement & Moho) Models of Sumatera Region

We present the first island-wide three-dimensional shear-wave velocity (Vs) model of the Sumatran crust derived from one year of ambient noise tomography (ANT) using data from 117 broadband stations of Indonesia’s permanent seismic network (IA-Net) over 12 months. Vertical-component empirical Green’s functions were retrieved from continuous noise cross-correlations, and Rayleigh-wave group velocity dispersion (8–34 s) was inverted to image structures down to ~40 km depth. The resulting Vs model reveals three tectonically distinct domains: (1) low-Vs anomalies (<3 km/s) delineate the North, Central, and South Sumatra back-arc basins containing 2–7 km of sediments that deepen northward; (2) high-Vs regions (3.0–3.8 km/s) beneath the Bukit Barisan volcanic arc indicate crystalline basement uplift, with a localized low-Vs zone (down to 15–20 km) beneath the Toba Caldera consistent with a mid-crustal magmatic system; and (3) limited forearc depocenters correspond to shallow piggyback basins. The Sumatran Fault Zone (SFZ) appears as a crustal-scale velocity boundary separating arc and back-arc crust, spatially coincident with earthquake clustering.