Common image gathers in the offset domain are used extensively in velocity analysis, and AVO/AVA studies using a technique described by Bleistein (1987). Imaged with the correct background velocity model, the events will appear horizontal in the offset gathers. Any curvature or moveout in these gathers can be used as a criterion for updating migration velocities. If the geology is complex and the ray field becomes multipathed, the assumptions made for imaging data in the offset domain are violated. This will especially influence the quality of common image gathers and, hence, make it difficult to perform any form of AVA or velocity analysis. Such complicated problems arise typically in seismic imaging beneath gas clouds, salt, and basalt.

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