A method is disclosed for migrating seismic data. The method includes selecting an image point and generating an initial model of seismic velocity with respect to time. The initial model includes substantially horizontal layers each having a selected interval velocity and a selected thickness. A travel time of seismic energy is determined from at least one seismic energy source position to at least one seismic receiver position, wherein the seismic energy is reflected from the image point. A ray path is estimated from the at least one seismic source position to the image point and from the image point to the at least one seismic receiver position. The ray path is based on the source position, the receiver position and the velocity model at the image location. A two-way travel time of seismic energy through formations to the image point is then determined.
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