Migration artifacts and velocity analysis

An advantage of Kirchhoff depth migration is that it can perform common offset migration, which outputs common-offset image gathers (COIGs). These are typically used as input to a tomography program for velocity model building. For large surveys, the COIGs can be generated from relatively small common offset datasets which substantially reduces computational requirements in both memory and I/O. However, common offset migration generally encounters a migration ambiguity problem. As a result, the COIG displays strong artifacts when the imaging ambiguity is present. Therefore, it causes problems in velocity analysis because automatic event pickers may not be able to distinguish the artifacts from true events. When artifacts are picked, conventional tomography fails for velocity estimation. In this paper, we propose a tomography algorithm which effectively uses both the reflected events and artifacts in COIGs. It provides the correct velocity update even when artifacts have been picked. A GOM case shows promising results.