The orientation and depth of deformation in the Earth is characterized by seismic anisotropy-variations in the speed of passing waves caused by the alignment of minerals under strain into a preferred orientation. Seismic anisotropy in the western US has been well studied and anisotropy in the asthenosphere is thought to be controlled by plate motions and subduction. However, anisotropy within the crust and upper mantle and the variation of anisotropy with depth are poorly constrained. Here, we present a three-dimensional model of crustal and upper mantle anisotropy based on new observations of ambient noise and earthquake data that reconciles surface wave and body wave data sets. We confirm that anisotropy in the asthenosphere reflects a mantle flow field controlled by a combination of North American plate motion and the subduction of the Juan de Fuca and Farallon slab systems. We also find that seismic anisotropy in the upper mantle and crust are largely uncorrelated: patterns of anisotropy in the crust correlate with geological provinces, whereas anisotropy in the upper mantle is controlled by temperature variations. We conclude that any coupling between anisotropy in the crust and mantle must be extremely complex and variable.
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机译：地球变形的方向和深度以地震各向异性为特征，地震波的传播速度是由应变作用下的矿物排列成优选方向所引起的。对美国西部的地震各向异性已经进行了充分的研究，并且认为软流圈中的各向异性受板块运动和俯冲控制。然而，地壳和上地幔内部的各向异性以及各向异性随深度的变化很难得到约束。在这里，我们基于环境噪声和地震数据的新观测结果提出了地壳和上地幔各向异性的三维模型，该模型使表面波和体波数据集协调一致。我们确认，软流圈中的各向异性反映了由北美板块运动以及Juan de Fuca和Farallon平板系统的俯冲作用共同控制的地幔流场。我们还发现上地幔和地壳的地震各向异性在很大程度上是不相关的：地壳中的各向异性模式与地质省相关，而上地幔的各向异性是由温度变化控制的。我们得出结论，地壳和地幔各向异性之间的任何耦合都必须极其复杂和多变。
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