三维TTI介质高效射线追踪方法

TTI介质是石油地震勘探领域最常用的各向异性介质，快速计算TTI介质射线路径和走时信息有重要的研究意义.TTI介质传统运动学射线追踪方法一般基于任意弹性介质射线方程，利用Bond变换或者四阶张量变换来处理复杂的21个弹性参数，因而非常耗时.实际野外对称轴统一的TTI介质模型，一般可以看成VTI介质模型旋转一定角度获得.为此，本文推导了三维VTI介质射线追踪方程，提出先在本构坐标系中进行VTI介质射线追踪，再通过坐标旋转将射线路径旋转至观测坐标系中，获得TTI介质射线路径.数值模型计算表明该方法高效和精确，较传统方法效率提高了近4倍.在强各向异性等特殊情况下，体波波前面都与理论群速度面一致.

A high-efficiency ray-tracing method for 3-D TTI media

The TTI medium is one of the most commonly used anisotropic materials in seismic prospecting. Thus, study on rapid calculation of ray paths and travel time in a 3-D TTI medium is a significant subject. Because 21 elastic parameters of the TTI medium are usually nonzero, the traditional method needs to use the Bond transformation and the most complicated ray tracing equations to do ray tracing for this medium. A multiple-layer TTI model can be treated as a VTI model by utilizing coordinate transformation. Thus, on contrast to the traditional method, we derive the ray tracing equations of the 3-D VTI medium and then utilize 3-D VTI ray tracing equations and coordinate transformation to acquire trajectory and traveltime of body waves in the TTI medium. Theoretical analysis and CPU time consuming analysis show that the efficiency of our method is about 4 times higher than that of the traditional method. To examine the feasibility of this method, we build four single layer models and two multilayer models. The experiments on these models indicate that the wavefronts of P, SV and SH waves are exactly the same as the theoretical group velocity surface even in strong anisotropic models and other special cases.