Modeling Body and Surface Wave Anisotropy in 3-D Media with a Case Study in Iceland

地震各向异性对岩石圈的变形和软流圈的地幔流动模式提供了重要的约束。径向各向异性可以通过瑞利波和洛夫波色散测量；方位角各向异性通常由SKS相的剪切波分裂和瑞利波层析成像得到。然而，两种方法的方位各向异性结果在许多地区并不一致，例如在科罗拉多落基山脉、冰岛和澳大利亚。这种差异部分是由于体波和面波的不同性质造成的。例如，SKS分裂反映了从核幔边界到地表各向异性的整体结果，而周期小于100 s的瑞利波主要对200 km以上的地球进行采样。这种差异也可以归因于许多其他因素，包括横向非均质性和各向异性之间的权衡，各向异性的三维变化，以及有限的频率。本研究的目的是探讨一般情况下横波分裂各向异性与瑞利波各向异性之间的差异。上面列出的可疑原因将单独研究。我们提出在各种三维非均质和各向异性模型中，采用平行伪谱法计算SKS相和面波的合成波形。该方法已成功地应用于剪切波分裂的模拟。伪谱法模拟表面波的实验还将继续进行。将剪切波分裂技术和双平面波反演方法应用于合成资料，反演各向异性和非均质性。提出的研究将提高我们对体波和面波方位各向异性差异的认识。

Seismic anisotropy provides important constraints on deformation in the lithosphere and mantle flow patterns in the asthenosphere. Radial anisotropy can be measured from Rayleigh and Love wave dispersions; and azimuthal anisotropy is often obtained from shear-wave splitting of SKS phases and from Rayleigh wave tomography. However, the results of azimuthal anisotropy from the two methods do not agree in many areas, such as in the Colorado Rockies, Iceland, and Australia. Part of the discrepancy is due to the different properties of body and surface waves. For example, SKS splitting reflects an integral result of anisotropy from the core mantle boundary to the surface while Rayleigh waves at periods less than 100 s primarily sample the earth above 200 km. The discrepancy can also be attributed to many other factors, including the tradeoff between lateral heterogeneity and anisotropy, 3-D variations of anisotropy, and the finite frequency. The goal of our proposed study is to investigate the discrepancy between shear-wave splitting anisotropy and Rayleigh wave anisotropy in general cases. The suspected reasons listed above will be studied individually. We propose to adopt the parallel pseudo-spectral method in computing synthetic waveforms of SKS phases and surface waves in various 3-D heterogeneous and anisotropic models. This method has been successfully applied in modeling shear-wave splitting. More experiments will be performed in modeling surface waves through the pseudo-spectral method. The shear-wave splitting technique and the two-plane-wave inversion method will be applied to the synthetic data to retrieve anisotropy and heterogeneity. The proposed study will improve our understanding about the discrepancy in azimuthal anisotropy from body and surface waves.