Shear‐wave splitting observations can provide insight into mantle flow, due to the link between the deformation of mantle rocks and their direction‐dependent seismic wave velocities. We identify anisotropy in the Cook Inlet segment of the Alaska subduction zone by analyzing splitting parameters of S waves from local intraslab earthquakes between 50 and 200 km depths, recorded from 2015–2017 and emphasizing stations from the Southern Alaska Lithosphere and Mantle Observation Network experiment. We classify 678 high‐quality local shear‐wave splitting observations into four regions, from northwest to southeast: (L1b) splitting measurements parallel to Pacific plate motion, (L1a) arc‐perpendicular splitting pattern, (L2) sharp transition to arc‐parallel splitting, and (L3) splitting parallel to Pacific plate motion. Forward modeling of splitting from various mantle fabrics shows that no one simple model fully explains the observed splitting patterns. An A‐type olivine fabric with fast direction dipping 45° to the northwest (300°)—aligned with the dipping slab—predicts fast directions that fit L1a observations well, but not L2. The inability of the forward model fabrics to fit all the observed splitting patterns suggests that the anisotropy variations are not due to variable ray angles, but require distinct differences in the anisotropy regime below the arc, forearc, and subducting plate.

中文翻译：

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基于板内地震的剪切波分裂的阿拉斯加俯冲带各向异性变化

由于地幔岩石的变形及其与方向有关的地震波速度之间的联系，剪切波分裂观测可以提供有关地幔流动的洞察力。我们通过分析2015-2017年记录的50至200 km深度的局部平板内地震的S波分裂参数，并强调阿拉斯加南部岩石圈和地幔观测网络实验的台站，来确定阿拉斯加俯冲带库克湾段的各向异性。我们将678个高质量的局部剪切波分裂观测分为西北至东南四个区域：（L1b）与太平洋板块运动平行的分裂测量，（L1a）弧垂直分裂模式，（L2）急剧过渡到弧平行分裂，并且（L3）分裂平行于太平洋板块运动。从各种地幔织物分裂的正演模型表明，没有一个简单的模型可以完全解释所观察到的分裂模式。一种A型橄榄石结构，其快速方向向西北（300°）倾斜45°（与倾斜平板对齐），可以预测快速方向，该方向很适合L1a观测，但不适合L2。前向模型织物无法适应所有观察到的分裂图案，这表明各向异性的变化不是由于可变的射线角度引起的，而是要求电弧，前臂和俯冲板下方的各向异性状况存在明显差异。但不是L2。前向模型织物无法适应所有观察到的分裂图案，这表明各向异性的变化不是由于可变的射线角度引起的，而是要求电弧，前臂和俯冲板下方的各向异性状况存在明显差异。但不是L2。前向模型织物无法适应所有观察到的分裂图案，这表明各向异性的变化不是由于可变的射线角度引起的，而是要求电弧，前臂和俯冲板下方的各向异性状况存在明显差异。