Seismic imaging beyond depth migration

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Abstract
If seismic imaging is formulated in terms of two focusing steps—focusing in emission and focusing in detection (or vice versa)—the output of the first focusing step yields a new type of seismic gather, the common-focus-point (CFP) gather, which is available for data analysis and information extraction. One important consequence of this novel option is that the involved focusing operators can be updated without updating the underlying velocity model. Introducing the concept of “dynamic focusing,” it is proposed to verify the validity of focusing operators by comparing the “gather of focus-point responses” with the “gather of focusing operators.” Compared with velocity-driven time and depth migration, operator-driven CFP migration can be considered as the most general approach to seismic imaging: it does not require a velocity model, and it automatically takes into account unknown complex propagation effects such as conversion, anisotropy, and dispersion. In addition, in CFP migration, the second focusing step can be extended to produce both angle-averaged reflection information and angle-dependent reflection information. The CFP approach to seismic migration allows new solutions in the situation of complex near-surface layers, sub-salt targets, multicomponent processing, and time lapse analysis.

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