Crustal and Upper Mantle Structure Beneath Sumatra Based on Seismic Ambient Noise Tomography

Located on the subduction boundary between Indo-Australia and Eurasia plates, the Sumatra region is considered as one of the most active tectonic regions in the world. The existence of the Sumatran trench, abundant arc volcanism, as well as multiple fault segments on the mainland make this region a suitable place to study crustal and upper mantle structures. Furthermore, studying the structures of the arc and the overriding lithosphere is crucial for understanding the tectonic evolution and geohazard potential in Sumatra, particularly in relation to megathrust earthquakes and arc volcanism. The goal of this study is to image the shear wave structure of the crust and upper mantle beneath Sumatra based on ambient noise tomography. We incorporate three seismic networks in this region for the continuous data from January 2022 to December 2023 from 140 broadband stations. We construct Rayleigh wave group and phase velocity maps for 10-60 s using Fast Marching Surface Tomography and then invert these for the shear wave structure with applying transdimensional Bayesian inversion method. The obtained model in the shallower depth shows prominent low velocity near the Sumatra trench probably associated with the mantle wedge. On the other hand, high velocities primarily detect the geometry of the lithosphere beneath Sumatra. In the deeper part, high velocity delineates the subduction slab beneath this region and low velocity may define magma structure beneath major volcanoes, such as the Toba caldera. With further interpretation, the result can contribute to better understanding of the development of the major arc volcanoes in a relationship with the slab subduction and associated modification of the overriding lithosphere.