Direct probabilistic inversion of shear wave data for seismic anisotropy
Direct probabilistic inversion of shear wave data for seismic anisotropy
复制标题
地震各向异性剪切波数据的直接概率反演
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发表时间：
2012
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通讯作者：
J. Wookey
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作者：
J. Wookey
总而言之，横波分裂可能是各向异性材料对地震波传播影响的最明确的标志。它已被广泛用于研究地球各向异性，在全球范围内从内核到最上部地幔和地壳的构造，以及在较小尺度上成像油气藏中的变形。已有成熟的技术用于测量单个(三分量)地震记录中的横波分裂，最近这些技术已扩展到以层析方式处理横波分裂：使用分裂测量的大数据集确定非均匀各向异性模型。在这里，我建议对最近的横波分裂层析成像方法进行扩展，该方法将数据分析结合到反演本身中。该方法使用非线性邻域算法反演来探索由多个均匀区域组成的各向异性模型所定义的参数空间。通过将其预测的分裂应用于整个数据集来评估每个候选模型。这种方法的计算代价很高，但很容易并行化。我将该方法应用于三个简单的合成案例，以证明该方法的实用性。最后，我将该方法应用于从SKS分裂推断两层各向异性的问题，这是全球地震学中经常尝试的问题。这使用了来自EKTN地震台的数据，在那里之前已经推断出两层分裂。这突出了这类研究的一些内在权衡，并强调需要纳入额外的信息来解决这些问题。该方法适用于从全球到储集层的各种情况下的横波各向异性分析。
SUMMARY Shear wave splitting is perhaps the most unambiguous signature of the effect of anisotropic materials on the propagation of seismic waves. It has been used extensively to study anisotropy in the Earth, at global scales from the inner core to the tectonics of the uppermost mantle and crust, and at smaller scales for imaging deformation in hydrocarbon reservoirs. Wellestablished techniques exist for measuring shear wave splitting in a single (three-component) seismogram and more recently these have been extended to treat shear wave splitting in a tomographic fashion: determining non-uniform anisotropic models using large data sets of splitting measurements. Here, I propose an extension to a recent shear wave splitting tomography methodology which incorporates the data analysis into the inversion itself. This methodology uses a non-linear neighbourhood algorithm inversion to explore the parameter space defined by an anisotropic model consisting of a number of uniform domains. Each candidate model is assessed by applying the splitting it predicts to the entire data set. This approach is computationally expensive, but is highly amenable to parallelization. I apply the methodology to three simple synthetic cases to demonstrate the utility of the method. Finally, I apply the approach to the problem of inferring two-layer anisotropy from SKS splitting, which is a commonly attempted problem in global seismology. This uses data from the seismic station EKTN, where two-layer splitting has been previously inferred. This highlights some of the inherent trade-offs with such studies, and emphasizes the need to incorporate extra information to resolve these. This method is applicable to shear wave anisotropy analysis in a broad range of settings from global to reservoir scale.