Abstract: A method for improving velocity models so that constant-offset migrations estimate consistent positions for reflectors includes tomographic estimation of seismic transmission velocities from constant-offset depth migrations. A method of converting inconsistencies in reflector positioning from constant-offset migrations into equivalent errors in modeled travel times is introduced, so that conventional methods of traveltime tomography can improve the velocity model. An improved velocity model allows a more accurate migrated image of the subsurface. The estimated velocity model can also detect anomalous regions of geologic significance, such as low velocity gas accumulations and irregular near surface weathering. In an alternate embodiment the procedure can be iterative and allow alternating improvements in the positions of reflectors and in the velocity model.