Wave-equation shear wave splitting tomography
Wave-equation shear wave splitting tomography
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DOI：
10.1111/j.1365-246x.2007.03632.x
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发表时间：
2008
影响因子：
2.8
通讯作者：
M. Long;M. Hoop;R. Hilst
中科院分区：
文献类型：
--
作者：
M. Long;M. Hoop;R. Hilst
本文的主要重点是（宽带）剪切波分裂测量的层析反演在上地幔各向异性结构的理论框架的发展。我们发现，偏微分方程（PDE），治理波动方程剪切波分裂层析成像，线性化后与玻恩近似，类似的结构方程描述波动方程透射和反射层析成像。对于完整的宽带分析，这些偏微分方程可以进行数值计算，但我们在这里显示的领先阶渐近（即“射线”）的相关有限频率灵敏度内核的行为。为了简单起见，我们假设各向异性模型在一个水平方向上是不变的。这种2.5维的几何结构非常适合于研究与岩石圈板块俯冲有关的上地幔各向异性，如果沟板系统近似为2维的话。以所谓的分裂强度作为数据拟合的度量，在弱各向异性的假设下，我们推导出灵敏度核的表达式。我们关注描述倾斜横向各向同性的两个各向异性参数：对称轴相对于水平面的倾角θ 0和代表各向异性强度的非椭圆率参数λ A，我们说明了均匀和非均匀（各向异性）背景模型的有限频率效应。在非均匀介质中的敏感性核计算的初始模型从数值模拟的流和有限应变下的琉球弧。在非均匀介质中计算的核与均匀背景中的核有很大不同。这证明了迭代模型（和内核）评估的重要性，以达到有限频率层析成像的全部（分辨率）潜力。
The main focus of this paper is the development of a theoretical framework for the tomographic inversion of (broad-band) shear wave splitting measurements in terms of anisotropic structure in the upper mantle. We show that the partial differential equations (PDEs) that govern wave equation shearwave splitting tomography are, upon linearization with the Born approximation, similar in structure to the equations that describe wave equation transmission and reflection tomography. For full broad-band analysis these PDEs can be evaluated numerically, butwe show here the leading order asymptotic (i.e. ‘ray born’) behaviour of the associated finite-frequency sensitivity kernels. For simplicity we assume that the anisotropic model is invariant in one horizontal direction. This 2.5-D geometry is well suited for studying upper-mantle anisotropy associated with subduction of lithospheric plates if the trench-slab system is approximately 2-D.With the so-called splitting intensity as the metric for data fit, and under the assumption of weak anisotropy, we derive expressions for the sensitivity kernels.We focus on two anisotropic parameters that describe tilted transverse isotropy: the dip θ 0 of the symmetry axis with respect to the horizontal plane and the anellipticity parameter ЄA, which represents the strength of the anisotropy.We illustrate the finite-frequency effects both for homogeneous and heterogeneous (anisotropic) background models. The sensitivity kernels in heterogeneous media are calculated for initial models obtained from numerical modelling of flow and finite strain beneath the Ryukyu arc. Kernels calculated in heterogeneous media differ substantially from those in a homogeneous background. This demonstrates the importance of iterative model (and kernel) assessment for reaching the full (resolution) potential of finite frequency tomography.