The Study And Application Of Velocity Model Building By Tomography With Irregular Surface

With the development of seismic exploration, the targets have been transferred to areas which have more complicated structures underneath and irregular surface, especially in the western of china with heterogeneous velocity laterally. And the efficiency of pre-stack depth migration lies greatly on the precision of velocity model building. Thus, the success of seismic exploration in such areas depends largely on the accuracy of velocity model building in depth domain.As to areas which have more complicated structures underneath and irregular surface, conventional velocity analysis methods needs to correct relief surface to datum. Velocity model building by tomography based on relief surface implement pre-stack depth migration from surface directly and it has a more precision than migration velocity analysis. Thus, it could improve the accuracy and efficiency with no limit of the surface.In tomography inversion, singular values of frechet matrix would give rise to the instability of inversion. So we must suppress the underdetermined and null space components to improve the stability and efficiency of tomography inversion. Through regularization, we can add prior information to tomography equations. In this thesis, we want to go deep into the application of regularization in tomography inversion and penetrate into velocity model building by tomography with irregular surface.In this thesis, we could get initial migration section and common imaging point gathers after pre-stack depth migration. And then we picked reflection points and reflector dip from migration section and implemented ray tracing to get frechet matrix. On the other hand, we have picked residual move-out from common imaging point gathers. Finally, through tomography inversion and infecting preconditioning smoother, we could invert velocity updates. Both model and real tests have proved that method in this thesis is efficient and robust.