Abstract This study presents observations of Love-to-Rayleigh scattering beneath the eastern North American passive margin that place new constraints on seismic anisotropy in the upper mantle. The scattering of Love-wave energy to Rayleigh waves is generated via sharp lateral gradients in anisotropic structure along the source-receiver path. The scattered phases, known as quasi-Love (QL) waves, exhibit amplitude behavior that depends on the strength of the anisotropic contrast as well as the geometrical relationship between the propagation azimuth and the anisotropic symmetry axis. Previous studies of seismic anisotropy in the upper mantle beneath eastern North America have revealed evidence for a mix of lithospheric and asthenospheric contributions, but the interpretation of indicators such as SKS splitting is hampered by a lack of vertical resolution. Complementary constraints on the depth distribution of anisotropy can be provided by surface waves, which have the additional advantage of sampling portions of the margin that lie offshore. Here we present measurements of QL phases using data from several hundred broadband seismic stations in eastern North America, including stations of the USArray Transportable Array, the Central and Eastern U.S. Network, and the MAGIC experiment in the central Appalachians. We find evidence for clear QL arrivals at stations in eastern North America, consistent with a region of particularly strong and coherent scattering inferred just offshore the central portion of the margin. The coherent scattering near the Eastern North American Margin likely reflects lateral transitions in seismic anisotropy in the asthenospheric mantle, associated with locally complex three-dimensional flow, with possible additional contributions from anisotropy in the mantle lithosphere. A second region of strong QL scattering near the southern coast of Greenland is enigmatic in origin, but may be due to pre-existing lithospheric fabric.

中文翻译：

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横跨北美东部被动边缘的 Love-to-Rayleigh 散射

摘要 本研究介绍了对北美东部被动边缘下方的 Love-to-Rayleigh 散射的观测，这些观测对上地幔的地震各向异性施加了新的限制。洛夫波能量向瑞利波的散射是通过沿源 - 接收器路径的各向异性结构中的急剧横向梯度产生的。被称为准爱 (QL) 波的散射相位表现出的振幅行为取决于各向异性对比的强度以及传播方位角和各向异性对称轴之间的几何关系。先前对北美东部下地幔上地幔地震各向异性的研究揭示了岩石圈和软流圈混合贡献的证据，但由于缺乏垂直分辨率，SKS分裂等指标的解释受到阻碍。表面波可以提供对各向异性深度分布的补充约束，其具有对位于海上的边缘部分进行采样的额外优势。在这里，我们使用来自北美东部数百个宽带地震台站的数据展示了 QL 相位的测量结果，包括 USArray 可移动阵列台站、美国中部和东部网络以及阿巴拉契亚中部的 MAGIC 实验。我们在北美东部的台站发现了清晰的 QL 到达的证据，这与推断出的边缘中央部分离岸特别强烈和相干散射的区域一致。北美东部边缘附近的相干散射可能反映了软流圈地幔中地震各向异性的横向转变，与局部复杂的三维流动相关，地幔岩石圈中的各向异性可能有额外的贡献。格陵兰南部海岸附近的第二个强 QL 散射区域的起源是个谜，但可能是由于预先存在的岩石圈结构。