Prestack multicomponent migration

Prestack elastic migration by displacement potential extrapolation is a mixed, systematic, and function-blocked vector wavefield migration algorithm. A new wavefield extrapolation method for inhomogeneous media is introduced here according to the following sequence: displacements --> potentials --> extrapolation of the potentials --> displacements, which is relatively accurate and not computer-time intensive. Traveltimes of both direct downgoing P- and S-waves, which are necessary in elastic migration, are calculated with a modified convolutional acoustic forward modeling program applicable to complex structures. A new image condition based on the time consistent principle is developed. It involves first obtaining an image condition section. Then two images (PP and SS) are obtained from the product of the extrapolated and decomposed PP- and SS-wave displacement amplitudes and the image condition section. All PP-, PS-, SP- and SS-waves are considered when the image condition section is calculated. The image condition section minimizes cross-talk between modes. Compared to previous treatments, the newly developed image condition formula is superior since it allows migration of multicomponent seismic data produced using a combined P and S source. Numerical test results are very encouraging and clearly demonstrate the robustness of the technique. Further work is continuing so as to overcome ray angle and polarity problems in the image condition.