Structural Heterogeneity of the Alaska‐Aleutian Forearc: Implications for Interplate Coupling and Seismogenic Behaviors

Abstract

AbstractWe determine high‐resolution 3‐D seismic images (Vp, Vs, and Vp/Vs) of the Alaska‐Aleutian forearc region, which are used to further estimate the serpentinization volume fraction of the subducting Pacific slab. Our results show that the hydration degree of the lower plate is high in the Shumagin Gap but relatively low in the Semidi and Kodiak segments, which roughly shows a trend of eastward decrease that is correlated with an increase of the interseismic slip deficit rate. The variation of slab serpentinization degree derived from our Vp model shows an uneven decreasing trend, well consistent with the along‐strike segmentation of interplate coupling and coseismic slip distributions of the 2020 Mw 7.8 Simeonof and 2021 Mw 8.2 Chignik megathrust earthquakes. The 2020 Mw 7.6 Sand Point earthquake took place within the strongly hydrated slab, whose occurrence was probably related to the variation of slip deficit rate that is probably affected by the changes in plate hydration. In addition, slow earthquakes occurred between the hydrated slab with pre‐subduction structures (e.g., bending faults, seamounts, and fracture zones) and the fluid‐saturated overriding crust and mantle wedge, where the intraslab seismicity and dehydration are intensive. These features suggest that lower‐plate hydration and dehydration may affect the interplate coupling and seismogenic behaviors in subduction zones.