Evaluation and determination of anisotropic parameters using multiple shear-wave splitting analysis methods
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摘要:
横波分裂分析是探测地球内部各向异性参数的重要方法.但数据的噪声水平、观测方位分布以及介质复杂程度均会影响横波分裂分析结果的稳定性，从而降低最终解的可靠性，甚至影响介质分层情况的判别.本文首先通过一系列理论测试，分析了旋转相关、最小能量和最小特征值三种横波分裂分析方法所得解随噪声水平、观测方位和介质分层情况的变化规律，发现三种方法分析结果既存在相似性也存在差异性；然后提出了利用这种相似性和差异性对最终解进行评估和确定的方案；最后将该方案应用于理论数据和南美实测数据的分析中.分析结果证明本文提出的方案不仅提高了单层或多层中的顶层介质各向异性参数的可靠性，而且可以有效鉴别介质的分层情况（单层或双层）.
Abstract:Shear-wave splitting analysis is an important method to detect anisotropic structures of the Earth's interior. However, the noise level, observation orientation and the complexity of the medium can affect the stability of the analysis results, thereby reducing the reliability of the final solution, and even affecting the discrimination of layered medium. We thus firstly conducted a series of synthetic tests to analyze the variation pattern of solutions from the RC, SC and EV methods related to the noise level, distribution of observation orientations and medium layering. The analysis shows that there are both similarities and differences among the solutions of the three methods. We then proposed a scheme to evaluate and determine the final solution based on such similarities and differences. And at last, we applied the proposed evaluation and determination scheme to analyze both the synthetic data and the real data taken from South America. The analysis results prove that our proposed scheme not only improved the reliability of the final anisotropic parameters of the single-layered (or the top layer of the multiple-layered) medium, but also effectively identified the layering of the medium (single or double-layered).
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图 1
横波分裂现象(下)及分析原理示意图(上)
Figure 1.
Sketch of shear-wave splitting phenomena (bottom) and its analysis principle (top)
图 2
利用RC、SC和EV方法反演横波分裂参数实例
Figure 2.
Example of shear-wave splitting analysis for a synthetic single-layer anisotropic model, by RC, SC and EV methods
图 3
不同噪声水平下单一观测方位反演结果
Figure 3.
Results for data with different noise levels observed from one BAZ.
图 4
不同噪声水平下全观测方位反演结果
Figure 4.
Results for data with different noise levels observed from multiple BAZ
图 5
三种方法解的误差与观测方位的关系
Figure 5.
Variation of solution misfit relative to BAZ for the RC, SC and EV methods
图 6
RC、SC和EV方法对双层各向异性介质模型的反演结果
Figure 6.
Inversion results by RC, SC and EV methods for two-layer anisotropic models
图 7
南美应用实例地震台站(三角)位置
Figure 7.
Location of the stations (triangles) in South America used for the real data example
图 8
两种方法对南美NBLA台站解的评估
Figure 8.
Results of the NBLA station in South America evaluated by two different methods
图 9
具有双层各向异性介质特征的南美台站分析实例
Figure 9.
Examples of two-layer anisotropy for two stations in South America
表 1
不同方法对不同噪声水平数据分析结果的均方根误差
Table 1.
Root-mean-square misfit for data with different noise levels by different methods
噪声水平 RC SC EV 三种方法综合 eφ eδt eφ eδt eφ eδt eφ eδt 20% 10 0.14 4 0.16 6 0.15 6 0.15 30% 14 0.13 6 0.18 9 0.18 9 0.17 40% 19 0.12 14 0.15 18 0.13 17 0.13 
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表 2
不同方法对不同噪声水平数据分析结果的均值和标准差
Table 2.
The mean and standard deviation for data with different noise levels by different methods
噪声水平 RC SC EV 三种方法合计 φ σφ δt σδt φ σφ δt σδt φ σφ δt σδt φ δt 20% 47 9 1.98 0.07 45 4 1.95 0.06 45 6 1.97 0.07 45±6.95 1.97±0.07 30% 50 13 2.00 0.09 48 6 1.95 0.10 50 7 1.96 0.09 49±8.77 1.97±0.10 40% 57 14 2.05 0.11 52 11 2.00 0.11 57 13 2.03 0.11 55±21.44 2.03±0.11
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