Conclusions

In vertically layered media, reflected events have a limited crossline offset at depth even in the worst-case scenario for common-azimuth geometry. This result confirms the robustness of common-azimuth migration and leads to its generalization obtained by downward continuing the data in a narrow strip around the zero crossline offset. Both narrow-azimuth migration methods that I propose in this paper achieve high efficiency by exploiting the common-azimuth equations to define an optimal range of crossline-offset wavenumbers.

Tests on synthetic data generated assuming a vertically layered medium show that very few (2 or 4) crossline offsets are needed to obtain migrated images with the correct kinematics.