The Forward Simulation Of Acoustic-elastic Coupled Media

In marine seismic exploration,two media are often encountered: the upper seawater and the lower solid.However,solids under seawater are the target areas we usually investigate.In order to explain the data collected during marine seismic exploration,the forward simulation of acoustic elastic coupled media are inevitably evolving.In the forward modeling of acoustic-elastic coupling media,it is necessary to pay special attention to the fact that the interface between fluid and solid needs to meet some boundary conditions.Ideally,the interface between fluid and solid can be assumed to be horizontal,and the boundary conditions at this time are easily satisfied.However,in actual situations,the interface between fluid and solid is curved,and the boundary conditions that need to be met are not easy to achieve.To solve this problem,we propose a new algorithm.We include the conditions that need to be met at the interface between the fluid and the solid in the proposed algorithm.According to the pressure component of the elastic wave field,the average value of the negative normal stress can be calculated.By substituting this relationship into the first-order velocity-stress elastic wave equation.We can get the acoustic-elastic coupling equation of two-dimensional isotropic media.The application of the proposed algorithm to the horizontal model,the stepped model and the sinusoidal model can confirm the correctness of our proposed algorithm.The algorithm proposed in this paper can not only simulate the propagation of the wave field when the interface between fluid and solid is horizontal,but also simulate the propagation of the wave field when the interface between fluid and solid is curved.The algorithm we proposed is more realistic and easy to implement.At present,the study of acoustic elastic coupled media still assumes that the solid of the acoustic elastic coupled media is isotropic,but this assumption is not in line with the actual situation.In this paper,wederive the solid media of acoustic elastic coupled media from isotropic media to anisotropic media,and propose an acoustic elastic coupled media based on transverse isotropic media with vertical symmetric axes(VTI)to improve the accuracy of forward modeling.Based on the relationship between the Thomsen parameter and the coefficient matrix of the anisotropic elastic wave equation,we transform the Thomsen parameter into a velocity model with anisotropic properties.In this paper,the forward modeling of acoustic-elastic coupled media is extended from two-dimensional to three-dimensional.We use a staggered grid finite difference method to simulate the propagation of a wavefield in a three-dimensional acoustic elastic coupled media.We obtain some snapshots of the wave field when the solid of the acoustic elastic coupled media is an isotropic media and a VTI media.When the solid of the acoustic elastic coupled media is a VTI media,We can observe the qP wave and qS wave that can not be observed in the isotropic media from the wave field snapshot.We can also find that the seismic records obtained by the method we use are more realistic.The algorithm proposed in this paper is of great significance for high-precision ocean numerical simulation.