A Novel 3-D Seismic Scattering and Intrinsic Attenuation Tomography and Its Application to Northern Sumatra

Studying the subsurface structure of volcanoes is crucial for understanding volcanic mechanisms, current status, and potential risks. However, the intricate physical and chemical processes occurring over geological timescales make it challenging to characterize subsurface features such as volcanic structures and hydrothermal systems. Given the highly attenuating nature of magma, 3-D scattering and intrinsic attenuation tomography are critical methods for advancing our understanding of tectonic, magmatic, and hydrothermal processes and their interactions. Previous imaging techniques, however, required substantial memory usage and long computational times, limiting their application to only 1-D velocity models. This paper proposes a novel sensitivity-kernel calculation method for imaging shear wave seismic scattering and intrinsic attenuation. This method has the advantages of dramatically reducing memory and computational costs, as well as incorporating a 3-D seismic velocity model. We apply this approach to illustrate the 3-D scattering and intrinsic attenuation structures beneath the Toba volcano region in Northern Sumatra down to 20 km depth. Our results show high-intrinsic attenuation anomalies around the Toba caldera, revealing the magma chambers feeding the volcanoes. A conspicuous high-scattering attenuation anomaly is identified along the Great Sumatran Fault, possibly caused by the fault zone structure. Magmatism also likely contributes to the seismic activity south of the Toba caldera, as evidenced by the overlap of scattering and intrinsic attenuation anomalies.