Three-dimensional radial anisotropic structure of the North American upper mantle from inversion of surface waveform data
Three-dimensional radial anisotropic structure of the North American upper mantle from inversion of surface waveform data
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DOI：
10.1111/j.1365-246x.2007.03465.x
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发表时间：
2007-10
影响因子：
2.8
通讯作者：
F. Marone;Y. Gung;B. Romanowicz
中科院分区：
文献类型：
--
作者：
F. Marone;Y. Gung;B. Romanowicz
摘要 地震各向异性提供了对古和近期变形过程以及地幔动力学的深入了解。在建立以任意方向的对称轴为特征的北美上地幔各向异性模型的第一步中，旨在填补全球层析成像和 SKS 分裂研究之间的空白，我们在简正模渐近耦合理论 (NACT) 的框架内，同时反演了各向同性 S 速度结构和各向异性参数 xi = v 2 SH v2 扰动的长周期波形数据。由此产生的二维宽带灵敏度内核使我们能够同时利用长周期地震图中包含的基波和高模表面波的信息。为了确保反演的区域上地幔结构的高质量，精确的地壳校正至关重要。在这里，我们遵循一种超越线性扰动近似的方法，并将校正分为线性和非线性部分。反演数据集由 40 000 多个高质量三分量基波和泛音表面波形组成，这些波形是在北美宽带地震台记录的远震事件，并提供相当均匀的路径和方位角覆盖。我们的断层扫描模型的各向同性部分具有先前北美区域研究的大尺度特征。我们证实了西部活动构造区和中部/东部稳定地盾之间各向同性速度结构的显着差异，以及过渡区深度存在俯冲物质（胡安德富卡和法拉隆板块）。新的区域三维径向各向异性模型表明，在北美大陆克拉通部分下方存在两个不同的各向异性层：一个深层软流圈层，与当今的地幔流一致，另一个是较浅的岩石圈层，可能是古代构造事件的记录。
SUMMARY Seismic anisotropy provides insight into palaeo and recent deformation processes and, there- fore, mantle dynamics. In a first step towards a model for the North American upper mantle with anisotropy characterized by a symmetry axis of arbitrary orientation, aimed at filling the gap between global tomography and SKS splitting studies, we inverted long period waveform data simultaneously for perturbations in the isotropic S-velocity structure and the anisotropic parameter ξ = v 2 SH v2 , in the framework of normal mode asymptotic coupling theory (NACT). The resulting 2-D broad-band sensitivity kernels allow us to exploit the information contained in long period seismograms for fundamental and higher mode surface waves at the same time. To ensure high quality of the retrieved regional upper-mantle structure, accurate crustal cor- rections are essential. Here, we follow an approach which goes beyond the linear perturbation approximation and split the correction into a linear and non-linear part. The inverted data set consists of more than 40 000 high quality three component fundamental and overtone sur- face waveforms, recorded at broad-band seismic stations in North America from teleseismic events and provides a fairly homogeneous path and azimuthal coverage. The isotropic part of our tomographic model shares the large-scale features of previous regional studies for North America. We confirm the pronounced difference in the isotropic velocity structure between the western active tectonic region and the central/eastern stable shield, as well as the presence of subducted material (Juan de Fuca and Farallon Plate) at transition zone depths. The new regional 3-D radial anisotropic model indicates the presence of two distinct anisotropic layers beneath the cratonic part of the North American continent: a deep asthenospheric layer, con- sistent with present day mantle flow, and a shallower lithospheric layer, possibly a record of ancient tectonic events.