Multicomponent Prestack Reverse-time Migration Of Elastic Waves In Transversely Isotropic Medium With A Vertical Axis

Migration is the absolutely necessary of determining structural features in the data processing. Prestack depth migration is an effective way to imagine complex structure. Moreover, prestack reverse time migration is one of the most precise methods. Most crustal rocks are found experimentally to be anisotropic, only migration methods based on the anisotropic medium can increase migration accuracy. At present, multicomponent seismic exploration is being widely used. Multicomponent wavefields consists of a vertical and two horizontal components which satisfy the propagation laws of elastic waves and the information about the elasticity and lithology of the rocks can be acquired by full wavefields seismic prospecting. Making full use of multicomponent seismic records could effectively reduce the non-uniqueness in conventional primary wave exploration. Therefore, with the development of anisotropy and multicomponent exploration, it is essential to develop anisotropic multicomponent reverse time depth migration.In the prestack reverse time migration, computation of imaging time is the precondition of good migration result. Discreting the 2-D elastic velocity-stress wave equation in Vertical Transverse Isotropic (VTI) media by a high order staggered grid finite-difference scheme, this paper developed the forward extrapolation operator. According to that operator, imaging time of each grid is extracted by the amplitude of wave field during the reconstruction of exciting wave field. Owning to more practical wavefields reconstructed by wave theory, the imaging time is more precise.The reconstruction of reverse time wavefields is the key point that materializes the high accuracy of reverse time migration. Based on the theory of staggered grid, this paper developed the reverse-time extrapolation operator of 2-D VTI media elastic velocity-stress wave equation. According to that operator and the multicomponent records, received wavefields can be reconstructed. Seismic event truncation would bring artifacts to the reconstructing wavefields, so, a perfected match layer is introduced to decrease that influence.Getting the right image in the application of imaging condition is the direct influence of imaging quality and precision. High-amplitude low-frequency artifacts would occur above the layer and decrease the precision of image during the conventional imaging condition. In this paper, a new imaging condition was proposed by combining the Excitation-time Imaging Condition with the Poynting vector to remove low-frequency artifacts. It can keep advantage of two-way wave equation imaging precision and further increase imaging precision.Based on the theory above, this paper developed a 2-D elastic wave prestack reverse-time depth migration algorithm in the VTI medium. The algorithm was applied to synthetic records and the real data. The results show that this approach can produce clear images, remove low-frequency noises effectively, and have satisfactory practical application effect.