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The macro-velocity field has a decisive influence on seismic-wave imaging. Unfortunately, it is not easy to accurately estimate the velocity field from the seismic data. Up to now, the residual depth/time difference in the common-image gathers has been used for migration-velocity analysis (MVA) or inverting the macro-velocity distribution. However, in the case of complex topography and gelogical structures, MVA is not a successful approach. Therefore, seismic-wave imaging in complex survey areas has a long way to go.
We propose the following approach to inverting the macro-velocity field. The norm is defined as
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(48) |

where *k* stands for the iterative number; *U*_{S} is the calculated scattering wavefield. *R* is the position of the main reflectors, which can be identified from the migrated profile. is the slowness disturbance field. *W*_{1},*W*_{2} and *W*_{3} are the different weights.
According to Bleistein (2000,p.39), the calculated scattering wavefield can be given by
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(49) |

where .Alternatively, the calculated scattering wavefield () also can be given by
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(50) |

where is the slowness disturbance, *U*_{I} is the incident wave field, and *k*_{z} is the vertical wavenumber. The incident wave field *U*_{I} can be calculated with the following equation:
| |
(51) |

where , and .

** Next:** discussion and conclusion
** Up:** Wang and Shan: Imaging
** Previous:** Wavefield propagator
Stanford Exploration Project

5/3/2005