We estimate depth-dependent azimuthal anisotropy and shear wave velocity structure beneath the Alaska subduction zone by the inversion of a new Rayleigh wave dispersion dataset from 8 to 85 s period. We present a layered azimuthal anisotropy model from the forearc region offshore to the subduction zone onshore. In the forearc crust, we find a trench-parallel pattern in the Semidi and Kodiak segments, while a trench-oblique pattern is observed in the Shumagins segment. These fast directions agree well with the orientations of local faults. Within the subducted slab, a dichotomous pattern of anisotropy fast axes is observed along the trench, which is consistent with the orientation of fossil anisotropy generated at the mid-ocean ridges of the Pacific-Vancouver and Kula-Pacific plates that is preserved during subduction. Beneath the subducted slab, a trench-parallel pattern is observed near the trench, which may indicate the direction of mantle flow.

中文翻译：

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阿拉斯加俯冲带下方的地震方位各向异性


我们通过反演 8 至 85 秒周期的新瑞利波色散数据集来估计阿拉斯加俯冲带下方与深度相关的方位各向异性和剪切波速度结构。我们提出了从近海弧前区域到陆上俯冲带的分层方位各向异性模型。在弧前地壳中，我们在 Semidi 和 Kodiak 段发现了沟槽平行模式，而在 Shumagins 段则观察到了沟槽倾斜模式。这些快速方向与局部断层的方向非常吻合。在俯冲板块内，沿着海沟观察到各向异性快轴的二分模式，这与俯冲过程中保留的太平洋-温哥华板块和库拉-太平洋板块的洋中脊产生的化石各向异性的方向一致。在俯冲板片下方，在海沟附近观察到了与海沟平行的图案，这可能表明了地幔流的方向。