Study On Method Of Reverse Time Migration Of Quasi-p-waves In TI Media

The inverse time migration is a accurate offset method based on the two-way wave equation theory,which can accurately map the complex geological structure,especially for the large angle structure.Considering the large computational complexity of the elastic wave method and the difficulty of wave field separation,the isotropic hypothesis can not satisfy the human demand for complex underground miscellaneous structures.It is of practical significance to study the inverse of qP wave in anisotropic media.The inverse time migration(RTM)relies on wavefield extrapolation to image complex underground structures.The Lowrank approximation method is a new method to find the spatial-wavenumber domain matrix of wave field extrapolation in recent years.The biggest advantage of combining the Lowrank approximation method is to avoid the problem of qP wave equation derivation and the coupling equation decoupling difficult,and can eliminate the pseudo-shear wave interference completely and can adapt to the larger time step.This paper first introduces the basic principle of reverse-time migration,including forward extension and reverse continuation process,wavelet selection,boundary condition,imaging condition and suppression of low frequency noise.Then the concept and classification of the basic principles of anisotropic media are introduced.Then we introduce the RTM of qP wave of TI media based on Lowrank approximation proposed in this paper.This method avoids the complex derivation of the pure qP wave equation,and overcomes the limitation of the coupling equation to the model parameters,and can eliminate the pseudo-shear wave noise and the numerical dispersion.In the end,we present a large number of models for the proposed method.The forward modeling shows that the kinematic characteristics of the qP wave are accurate and the migration result of the waxian model shows that the TI medium qP wave inverse time migration method is correct.Comparing the proposed method with the traditional pseudo-acoustic method,the results show that the migration result of this method is obviously superior to the traditional method and the pseudo-shear wave noise is reduced.Finally,we use the reverse time migration method of quasi-P-waves in TI media based on the Lowrank approximation to test the complex TI model,and the results are good,which further shows that the method is suitable for the inverse time migration of anisotropic media.