横向各向同性介质中地震波走时模拟

横向各向同性介质是地球内部广泛分布的一种各向异性介质.针对这种介质，我们对各向同性介质的最小走时树走时模拟方法进行了推广，推广后的方法可适用于非均匀、对称轴任意倾斜的横向各向同性介质模型.为保证计算效率，最小走时树的构建采用了一种子波传播区域随地震波传播动态变化的改进算法.对于弱各向异性介质，我们使用了一种新的地震波群速度近似表示方法，该方法基于用射线角近似表示相角的思想，对3种地震波（qP, qSV和qSH）均有较好的精度.应用本文地震波走时模拟方法对均匀介质、横向非均匀介质模型进行了计算，并将后者结果与弹性波方程有限元方法的模拟结果进行了对比，结果表明两者符合得很好.本文方法可用于横向各向同性介质的深度偏移及地震层析成像的深入研究.

Seismic traveltime computation for transversely isotropic media

The minimum traveltime tree algorithm for tracing rays in isotropic media is extended to transversely isotropic(TI) media,which exist extensively in the Earth.The extended algorithm is suitable to heterogeneous TI media with tilted axes of symmetry.Construction of the minimum traveltime tree is implemented efficiently with a modified algorithm in which propagation areas of secondary waves are not fixed but adjusted dynamically with spread of seismic waves in media.As for weakly anisotropic media,we use a new approximate formula of group velocity in terms of ray angle.The approximate velocity formula is based on the expression of phase angle in terms of ray angle,and fits well the exact values for three independent modes of seismic waves(qP,qSV and qSH).Homogeneous and heterogeneous models are calculated with the extended minimum traveltime tree algorithm.We compare our results corresponding to the heterogeneous model with those obtained by a finite-element method for elastic anisotropic waves and find that they are in excellent agreement.The extended ray tracing method can be applied to further researches on depth migration and seismic tomography for TI media.