Love-to-Rayleigh scattering across the eastern North American passive margin
Love-to-Rayleigh scattering across the eastern North American passive margin
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DOI：
10.1016/j.tecto.2020.228321
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发表时间：
2020-02
期刊：
影响因子：
2.9
通讯作者：
Andrea Servali;M. Long;Jeffrey Park;M. Benoit;J. C. Aragon
中科院分区：
文献类型：
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作者：
Andrea Servali;M. Long;Jeffrey Park;M. Benoit;J. C. Aragon
这项研究提供了北美东部被动边缘下方Love-to-Rayleigh散射的观测结果，这对上地幔的地震各向异性施加了新的限制。勒夫波能量对瑞利波的散射是通过源-接收器路径各向异性结构中的尖锐横向梯度产生的。散射相称为准Love(QL)波，其幅度行为取决于各向异性对比度的强度以及传播方位和各向异性对称轴之间的几何关系。以前对北美东部上地幔地震各向异性的研究揭示了岩石圈和软流圈混合作用的证据，但由于缺乏垂直分辨率，对SKS分裂等指标的解释受到阻碍。面波可以提供对各向异性深度分布的互补约束，它还有一个额外的优势，即对近海边缘的部分进行采样。在这里，我们介绍了使用北美东部数百个宽带地震台站的数据来测量QL相位的情况，这些台站包括美国阵列移动台网、美国中部和东部网络以及阿巴拉契亚山脉中部的魔术实验。我们发现了明显的QL到达北美东部站点的证据，这与边缘中心部分近海推断的特别强烈和连贯的散布区域一致。北美东部边缘附近的相干散射可能反映了软流圈地幔地震各向异性的横向转变，与局部复杂的三维流动有关，可能还有地幔岩石圈各向异性的额外贡献。格陵兰岛南部海岸附近的第二个强QL散布区域的起源是个谜，但可能是由于先前存在的岩石圈组构。
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.