Abstract We use a dense network of observations and an automated method of analysis to investigate complex patterns of seismic anisotropy in the Pacific Northwest. We present SKS splitting results for approximately 220 broadband seismic stations, including 33 stations from the new Wallowa2 array deployed between 2016 and 2018 in northeast Oregon. Our data set contains approximately 3300 splitting measurements. Our anisotropy measurements indicate that anisotropy in the Pacific Northwest can be divided into two domains: near the subduction zone, anisotropy is perpendicular to the slab; and inboard of the subduction zone anisotropy tends to parallel the velocity structure and is roughly oriented with “absolute” plate motion. However, splitting analysis performs poorly in northeast Oregon, and results are not consistent with uniform or layered anisotropy. We argue that the complex splitting behavior in northern Oregon is a result of spatially variable upper mantle anisotropy, related to the complex upper mantle seismic structure. Interpreting the mantle anisotropy in this region requires methods not limited to standard ray theoretical shear wave splitting analysis.

中文翻译：

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太平洋西北部复杂的上地幔各向异性：来自SKS分裂的证据

摘要 我们使用密集的观测网络和自动分析方法来研究太平洋西北部复杂的地震各向异性模式。我们展示了大约 220 个宽带地震台站的 SKS 分裂结果，其中包括 2016 年至 2018 年间在俄勒冈州东北部部署的新 Wallowa2 阵列中的 33 个台站。我们的数据集包含大约 3300 个分裂测量值。我们的各向异性测量表明，太平洋西北部的各向异性可分为两个域：在俯冲带附近，各向异性垂直于板块；俯冲带内侧的各向异性趋向于平行于速度结构，并且大致以“绝对”板块运动为导向。然而，分裂分析在俄勒冈州东北部表现不佳，结果与均匀或分层的各向异性不一致。我们认为俄勒冈州北部复杂的分裂行为是空间可变的上地幔各向异性的结果，与复杂的上地幔地震结构有关。解释该区域的地幔各向异性需要的方法不仅限于标准射线理论横波分裂分析。