Elastic Reverse-time Migration In Anisotropy Media And GPU Acceleration

Migration is one of the most important step of determining structural features in the data processing. Prestack depth migration which came up with in recent years is an effective way to imagine complex structure underground. Prestack reverse time migration using full wave data to imagine, is one of the most precise methods of prestack depth migration. At the same time,The study of propagation and imaging of seismic wave in anisotropy is an important and frontier issue of seismic prospecting. We consider that the medium of earth is perfect elasticity and isotropy, but it is not. Using the method of solving isotropy problems will bring image error and reduce the resolution. Being a perfect approximation of anisotropy, assumption of isotropy can solve some practical problems, but because of the limit of accuracy and observation technology, it cannot show the anisotropy clearly, so we think the previous methods did not take enough attention to anisotropy. Prestack depth migration need a great deal of computation and memory of computer so as reverse time migration. However, it has an advantage of imaging and can solve some complex problems. At the same time, because we introduced anisotropic parameters, we need more computation and memory, so we follow with interest GPU which can bring us a fast operation to deal with our method. In conclusion, along with the develop of geophysical data processing technique, exploration technology of multicomponent and large offset application in the field, anisotropy needed to pay more attention to. Therefore, it is essential to develop anisotropic elastic reverse time migration with CPU-GPU collaborative computing.A important problem of elastic wave imaging is to separate wave filed and get pure p wave and s wave. For isotropy medium, using Helmholtz decomposition can solve that problem, but for anisotropy medium, because of the direction of wave propagation and wave shake deviation, is no longer same(p wave) and vertical(s wave), so if we use Helmholtz decomposition to separate wave filed we will get wave with interference, it will bring us perplexity when we imaging fine structure. This paper using improving pseudo p wave to separate wave filed, with two steps(first, simulation of isotropic, second, correction) to separate wave filed. It can get pure p wave and s wave to improve the imaging accuracy.In seismic wave imaging, boundary reflection is an important factor to influence the final results. There are two methods that are popular which is Perfected Matched Layer and absorb boundary condition, they both have advantages and disadvantages. This paper contrast the two methods and using hybrid absorbing condition(2012,Liu Yang), solve the boundary problems in elastic reverse time migration in anisotropy medium perfectly.Based on the research above, this paper actualized elastic reverse time migration of 2D VTI, HTI medium and using GPU to accelerate the speed of operation. The algorithm was applied to synthetic records and the real data. The results show that this approach can produce good images, and have satisfactory practical application effect.