A new imaging technique for reliable migration velocity analysis

SM1.4 SUMMARY In case of severe lateral velocity variations prestack depth migration is not suitable for migration velocity analysis. We therefore propose to substitute prestack depth migration by prestack imaging by coupled linearized inversion (PICLI). Results obtained with the Marmousi model show the improvement offered by this method for migration velocity analysis. PICLI involves a huge amount of computation. Hence we have paid special attention both to the solution of the forward problem and to the optimization algorithm. To simplify the forward problem we make use of paraxial approximations of the wave equation. Efficiency in the optimization algorithm is obtained by an exact calculation of the gradient by means of the adjoint state technique and by an adequate preconditioning. Doing so the above mentioned improvement is obtained at reasonable cost.