We have developed and implemented a new methodology using some variation of parsimonious migration to perform internal iterations inside the 3D grid tomography. First, we demigrate the common image gather's (CIG) significant reflection events (selected before by high grading the near offset stack) to get the unmigrated time gather data and related ray parameters. Second, we migrate the zero-offset event and reconstruct the computed unmigrated time gather data corresponding to the updated velocity model to derive the tomographic equation. The new approach is more accurate, rigorous and converges faster than other conventional tomography approaches. Since a migration engine is coupled with the tomography internal iterations, this approach has potential to reduce the number of prestack depth migration of seismic data while building a velocity model.

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