The Study Of3-D Ray Tracing Method Based On Wave Field Inversely Shooting

Seismic wave field forward modeling is the foundation of seismic inversion and geophysical tomography. For inverse problem, therefore, the forward problem as the first step of it is especially important. If there is not an effective forward modeling method, it is difficult to guarantee a satisfactory inversion results. In order to solve the inverse problem, it often has to solve the forward problem in the first place. As a rapid and effective approximately method of wave field, ray tracing method is able to understand and research the geological structure effectively. Its theoretical basis is that under the condition of high frequency approximation, the main energy of seismic wave field propagates along the ray path. Ray tracing method is not only significant for the seismic wave theory and seismic wave propagation problem, but also widely used in the earthquake location, seismic inversion and migration imaging process, thus it more and more gets the attention of geophysicists.Ray tracing method mainly includes two forward modeling method based on wave theory and ray theory. Among them, the forward modeling method based on the wave theory mainly reveals the dynamics of the seismic wave, and the forward modeling method based on the ray theory mainly reveals the kinematics of the seismic wave. Kinematical ray tracing is the base of dynamic ray tracing. Compared with the forward modeling method based on wave theory, forward modeling method based on ray theory although is incapable of simulating the wave field completely and accurately, but the advantage of it is high efficiency, realized in general machine, and the wave field can be artificially controlled and easily to identify and explain. Ray theory are used in many aspects, synthetic seismogram is just one of the aspects. In modeling research, ray theory and ray method is an important way of studying seismic wave propagation problem.The traditional ray tracing method includes shooting method of the initial value problem and bending method of the boundary value problem. The shooting method in this article correspondingly improves the traditional shooting method. It proposes three-dimensional ray tracing method based on the wave field inversely shooting. The traditional shooting method mainly shoots from shot points, it is difficult to solve the problem of multiple rays for each pair of source-receiver, and it has to shoot and iterate again for every change of observation system, leading to the slow computing efficiency. The basic idea of three-dimensional ray tracing method based on wave field inversely shooting in this article is testing through the control points in target layer, and iterating based on the target layer for each pair of source-receiver. It solves the problem of multiple rays existed for each pair of source-receiver in principle. At the same time, as long as the model does not change, the shooting result remains good. As long as the artillery position of observation system does not change, the iteration result remains good. This article improved the calculation method of the reflection ray and transmission ray direction, the reflected ray and the transmission ray direction calculation formula based on the reflection theorem and refraction theorem are deduced, which is the simplified algorithm of three-dimensional ray direction. It solves the problem of the linear equations. The normal vector calculation method of any point in the triangle is proposed in this paper to solve the problem that the effect is not very good in irregular surface of the traditional practice. This paper puts forward the intersection point calculation method of the space radiation and interface to solve the problem of how to quickly calculate the intersection point with intersected triangle and quickly judge whether the point is the true intersection point, and rapidly rule out a large number of no intersection triangles to improve the speed of the ray tracing by introducing layer face regionalization algorithm for intersection judgment.The method in this paper is able to find more effective and accurate rays, and enhance the accuracy of CRP statistical data. The computational efficiency in practice has significantly improved, and its efficiency is about the same as the commercial software of the green mountain. It is suitable for the3-d ray tracing engineering application in complex geological structure. This method solves the problem that the traditional ray tracing method has not solved.