In subduction zones, along-strike and downdip variations in megathrust slip behavior are linked to changes in properties of the subducting and overriding plates. Although marine geophysical methods provide insights into subduction zone structures, most surveys consist of sparse 2D profiles, limiting our understanding of first-order controls. Here, we use active-source seismic data to derive a 3D crustal-scale P-wave velocity model of the Alaska Peninsula subduction zone that encompasses both plates and spans the Semidi segment and SW Kodiak asperity. Our results reveal modest variations within the incoming plate, attributed to a series of fracture zones, seamounts and their associated basement swell, collectively contributing to plate hydration. Basement swell appears to modulate the distribution and type of sediment entering the trench, likely impacting observed variations in slip behavior. The overriding plate exhibits significant heterogeneity. The updip limit and width of the dynamic backstop are similar between the SW Kodiak asperity and eastern Semidi segment, but differ significantly from the Western Semidi segment. These distinctions likely account for differences in earthquake rupture patterns and interseismic coupling among these segments. Additionally, high-velocities in the mid-lower forearc crust coincide with the location of megathrust slip during the Mw 8.2 2021 Chignik event. We interpret these velocities as intracrustal intrusions that contributed to the deep rupture of the 2021 event. Our findings suggest that the contrasting structural and material properties of both the incoming and overriding plates influence the spatially complex and semi-persistent segmentation of the megathrust offshore the Alaska Peninsula.

中文翻译：

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从阿拉斯加半岛俯冲带的 3D 地壳尺度 P 波速度模型推断的巨型推力滑移行为的结构控制


在俯冲带中，大逆冲滑移行为的沿走向和下倾变化与俯冲板块和覆盖板块的性质变化有关。尽管海洋地球物理方法可以深入了解俯冲带结构，但大多数调查由稀疏的 2D 剖面组成，这限制了我们对一阶控制的理解。在这里，我们使用主动源地震数据得出阿拉斯加半岛俯冲带的 3D 地壳尺度 P 波速度模型，该模型包括两个板块，跨越塞米迪段和 SW Kodiak 凹凸度。我们的结果揭示了进入板块内的适度变化，这归因于一系列裂缝带、海山及其相关的基底膨胀，共同促进了板块水化。基底涌浪似乎调节了进入沟槽的沉积物的分布和类型，可能会影响观察到的滑移行为变化。覆盖板表现出显著的异质性。SW Kodiak 凹凸度和东部塞米迪段之间动态后盾的上倾限制和宽度相似，但与西部塞米迪段有很大不同。这些区别可能是这些段之间地震破裂模式和地震间耦合差异的原因。此外，中下前弧壳中的高速与 Mw 8.2 2021 Chignik 事件期间大逆冲滑移的位置相吻合。我们将这些速度解释为导致 2021 年事件深度破裂的地壳内侵入。我们的研究结果表明，入射板块和覆盖板块的截然不同的结构和材料特性影响了阿拉斯加半岛近海大逆冲的空间复杂和半持久分割。