Discussion and Conclusion

In this chapter, I proposed a new method for migrating prism waves by RTM. There are two steps to the method: (1) Conventional RTM is applied to the data to estimate the geometry of the horizontal reflectors near the salt flank; (2) Prism wave RTM is applied to the data again, except the prism imaging condition is used rather than the conventional one. Dip filtering can also be applied to the images to reduce noise. For the simple L model, the vertical reflector is not visible in the conventional RTM image, but it is well imaged by migration of the prism waves with a homogeneous velocity model. In the example of the salt model, the salt flank can be imaged by embedding the horizontal reflectors in the velocity model, which is not trivial, but the best image is obtained by summation of two dip filtered partial migration images: one from conventional RTM and the other from the migration of the prism waves. The disadvantage of prism wave RTM is that its computational cost is twice that of conventional RTM. The empirical results suggest that the proposed method can migrate the prism waves correctly to delineate salt flanks and improve the image quality with the help of dip filtering. =4