3D traveltime tomography of the Alaska subduction zone through inversion of active source data acquired during the Alaska Amphibious Community Seismic Experiment (AACSE)

Subduction zones are one of the world's primary sources of natural disasters, generating volcanic eruptions, earthquakes, and tsunamis. The Alaska Peninsula subduction zone is one such area that regularly ruptures in great earthquakes. This includes the Semidi segment, which ruptured in two Mw 8.2 events in 1931 and 2021, and the neighboring segment, called the Kodiak asperity, that last ruptured during the 1964 Mw 9.2 Prince William Sound earthquake. Although both segments of this subduction zone have ruptured in great earthquakes, they exhibit remarkable along-strike and downdip variations in seismicity at all depths, the style of great earthquakes, and present-date plate coupling. While many such features are documented, our understanding of the extent to which variable structure and composition of the overriding plate plate and/or physical properties and features of the incoming plate control these variations remains limited. To help address these limitations, we performed 3D first-arrival traveltime tomography of the Alaska Peninsula subduction zone using controlled source data recorded by the array of seismometers deployed as part of the Alaska Amphibious Community Seismic Experiment (AACSE). Our model space encompasses both plates and spans a nearly 500 km by 350 km area from the southwest Semidi segment to Kodiak Island. First-arrival traveltime inversion of the active source data (up to 200 km source-receiver offset) shows the recovery of P-wave velocity structure down to ~30 km depth and long-wavelength variations within both plates. Prominent features include the observation of higher velocities (approaching 6 km/s) in the upper forearc of the western Semidi segment as compared to those near the Kodiak asperity, as well as noticeable variations within the crust and upper mantle along the incoming plate. To further explore the origin of these variations and their potential consequences, we will compare our results with gravity and magnetic anomalies that are likely associated with nearby hotspot magmatism and extensive fracture zones within the incoming plate as well as differences in composition within the overriding plate.