SUMMARY The scattered teleseismic body waves have been used intensively to characterize the receiver-side lithospheric structures. The routinely used ray-theory-based methods have limitations to image complex structures and tackle strong heterogeneities. The newly developed wave-equation based, passive-source reverse time migration (RTM) approach can overcome such limitations. To date, passive-source RTM has been developed only for isotropic media. However, at least to the first-order, most lithospheric structures possess effective transverse isotropy with spatially variable symmetry directions. It is important to know the magnitudes of imaging errors that may be introduced by passive-source RTM when seismic anisotropy is treated in an incorrect way. In this paper, we investigate the influence of elastic anisotropy on teleseismic P-to-S conversions at the lithospheric discontinuities and explain why an isotropic RTM may fail to focus the converted wavefields from the perspective of relative arrival time variations with backazimuth and shear wave splitting. Accordingly, we extend the passive-source RTM approach for imaging 3-D lithospheric targets possessing transverse isotropy from the following two aspects: First, the teleseismic recordings with direct P and converted S phases are reverse-time extrapolated using rotated staggered grid (RSG) pseudospectral method, which can tackle strong heterogeneity and transverse isotropies with symmetry axes in arbitrary direction; Secondly, the backward elastic wavefields are efficiently decomposed into vector anisotropic P and S modes to support accurate imaging.

中文翻译：

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用于成像岩石圈间断面的三维被动源各向异性逆时偏移

小结 散射远震体波已被广泛用于表征接收侧岩石圈结构。常规使用的基于射线理论的方法在成像复杂结构和处理强异质性方面存在局限性。新开发的基于波方程的无源源逆时偏移 (RTM) 方法可以克服这些限制。迄今为止，仅针对各向同性介质开发了被动源 RTM。然而，至少对于一阶，大多数岩石圈结构都具有有效的横向各向同性和空间可变的对称方向。当以不正确的方式处理地震各向异性时，了解被动源 RTM 可能引入的成像误差的大小非常重要。在本文中，我们研究了弹性各向异性对岩石圈不连续处远震 P-S 转换的影响，并从后方位角和剪切波分裂的相对到达时间变化的角度解释了为什么各向同性 RTM 可能无法聚焦转换波场。因此，我们从以下两个方面扩展了具有横向各向同性的 3-D 岩石圈目标成像的被动源 RTM 方法：首先，使用旋转交错网格 (RSG) 对具有直接 P 相和转换 S 相的远震记录进行反向外推伪谱方法，可以解决任意方向对称轴的强异质性和横向各向同性；其次，后向弹性波场被有效地分解为矢量各向异性 P 和 S 模式，以支持精确成像。