A New Method for High Resolution Imaging of Upper Mantle Anisotropy
A New Method for High Resolution Imaging of Upper Mantle Anisotropy
复制标题
上地幔各向异性高分辨率成像的新方法
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
S. Chevrot
中科院分区：
文献类型：
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作者：
S. Chevrot
总结
SKS波的横向分量的振幅测量，即所谓的分裂强度，可以用来形成一个非线性反问题，以成像上地幔各向异性的3-D变化。假设横向各向同性（或六边形对称），可以通过两个各向异性参数和描述对称轴方向的两个角度来参数化各向异性。它们也可以写成两个共线的伪向量。层析过程包括检索这些伪矢量的空间分布，因此类似于表面波矢量层析。空间分辨率是由低频SKS波对偏离射线路径的地震各向异性的敏感性决定的，推导了包含近场贡献的三维分裂强度敏感性核的表达式，并通过与基于有限元法的全波方程解的比较进行了验证。这些灵敏度内核是有效的对称轴的任何方向，从而概括了以前的结果，仅适用于水平对称轴。结果表明，横向和垂直亚波长变化的各向异性可以检索与密集阵列的宽带站，即使在垂直传播的SKS波的情况下。
SUMMARY
Amplitude measurements of the transverse component of SKS waves, the so-called splitting intensity, can be used to formulate a non-linear inverse problem to image the 3-D variations of upper mantle anisotropy. Assuming transverse isotropy (or hexagonal symmetry), one can parametrize anisotropy by two anisotropic parameters and two angles describing the orientation of the symmetry axis. These can also be written as two collinear pseudo-vectors. The tomographic process consists of retrieving the spatial distribution of these pseudo-vectors, and thus resembles surface wave vectorial tomography. Spatial resolution results from the sensitivity of low-frequency SKS waves to seismic anisotropy off the ray path. The expressions for the 3-D sensitivity kernels for splitting intensity are derived, including the near-field contributions, and validated by comparison with a full wave equation solution based upon the finite element method. These sensitivity kernels are valid for any orientation of the symmetry axis, and thus generalize previous results that were only valid for a horizontal symmetry axis. It is shown that both lateral and vertical subwavelength variations of anisotropy can be retrieved with a dense array of broad-band stations, even in the case of vertically propagating SKS waves.