Abstract: Utilizing the seismic travel-time catalog of Alaska from 2000 to 2016 provided by the International Seismological Centre (ISC), this study employs eikonal equation-based seismic tomography to invert the three-dimensional velocity structure of the subsurface in southern Alaska, resulting in a high-resolution P-wave velocity model for the region. The results reveal strong heterogeneity in the crustal structure. The low-speed anomalies in the crust align well with geological structures such as surface sedimentary basins. Distinct high-velocity anomalies are observed in the upper mantle, corresponding to the subducting Pacific plate. Above this high-velocity anomaly, a thin layer of low-velocity anomalies is present, presumably the Yakutat microplate subducting into the North American plate. The 2018 M_W7.1 Anchorage earthquake occurred at the boundary of this microplate, possibly triggered by relative motions between the subducting plate and the overriding plate. Beneath Spur Volcano, significant low-velocity anomalies are evident, possibly indicating the formation of magma channels and magma chambers characterized by strong low-velocity anomalies, influenced by the upwelling of fluids released by partial melt and dehydration of material during plate subduction. Conversely, high-velocity anomalies dominate beneath Redoubt Volcano, and the high-velocity anomaly representing the subducting slab is discontinuous, possibly suggesting plate tearing. The fluids released by the dehydration of the subducting plate, as well as the upward movement of high-temperature, partially-molten material along inclined channels, provide the material and energy sources for surface volcanic activity.

Key words: Southern Alaska, Seismic tomography, Crustal velocity structure, Subducting slab