Waveform inversion in triclinic anisotropic media—a resolution study
Waveform inversion in triclinic anisotropic media—a resolution study
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DOI：
10.1093/gji/ggv097
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发表时间：
2015-06
影响因子：
2.8
通讯作者：
D. Köhn;O. Hellwig;D. Nil;W. Rabbel
中科院分区：
文献类型：
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作者：
D. Köhn;O. Hellwig;D. Nil;W. Rabbel
地震全波形反演已被应用于具有一定对称性的简单弹性问题，如各向同性、横向各向同性或垂直横向各向同性介质。在本研究中，FW I的概念被推广到最一般的各向异性情况，具有21个独立的弹性材料参数，并且没有对称面(三斜)。除了简要介绍求解正演问题的三维有限差分格式和FWI优化算法外，我们还对简单的各向异性介质进行了灵敏度研究。这个测试问题由一个齐次的三斜各向异性全空间组成，它包含21个空间分离的球体。在每个球体中，弹性张量的一个分量偏离背景介质5%。可以系统地研究不同球体的分辨率、不同弹性参数之间的模糊性以及采集几何的影响。由于Triclinic正问题的高计算成本，必须在捕获几何上做出一些妥协。用平面波源代替点源，导致入射角的限制，从而使非对角弹性张量分量的分辨率大大降低。结果表明，尽管有这些限制，层析采集几何结构将能够通过FW I在一定程度上分辨单斜对称性。限制采集几何结构(例如，VSP与反射地震或仅反射地震组合)可显著减少可分辨张量元素的数量，严格依赖于覆盖的入射角。
Seismic full waveform inversion (FWI) has been applied to simple elastic problems with certain symmetries, such as isotropic, transverse isotropic or vertical transversely isotropic media. In this study, the FWI concept is extended to the most general anisotropic case with 21 independent elastic material parameters and no symmetry plane (triclinic). Beside a short description of the 3-D finite-difference scheme to solve the forward problem and the FWI optimization algorithm, we present a sensitivity study for a simple anisotropic medium. This test problem consists of a homogenous triclinic anisotropic full space, which contains 21 spatially separated spheres. In each sphere one component of the elastic tensor deviates by 5 per cent from the background medium. The resolution of the different spheres, ambiguities between the different elastic parameters, as well as the effect of the acquisition geometry can be systematically investigated. Due to the high computational costs of the triclinic forward problem a few compromises have to be made regarding the acquisition geometries. Point sources are replaced by plane wave sources which lead to a limitation of incidence angles and therefore a strong decrease in resolution of the nondiagonal elastic tensor components. It is shown that, despite these limitations, a tomographic acquisition geometry would be able to resolve to some extent a monoclinic symmetry via FWI. Restricting the acquisition geometries (e.g. VSP combined with reflection seismic or reflection seismic only) significantly reduces the number of resolvable tensor elements in strict dependence of the covered incidence angles.