A programmable computer is used to perform the following. 3D seismic data sets, corresponding to each azimuth in seismic data obtained from a multi-azimuth marine seismic survey, are migrated in grids oriented with the corresponding azimuth. Acquisition geometry is stored for each trace in the seismic data sets for each azimuth. Residual analysis, based on the corresponding azimuth, is performed on each of the migrated data sets, generating residuals and reflectors for each azimuth. The residuals and reflectors generated for each azimuth are rotated and merged on a master grid. Reflection tomographic inversion is applied iteratively to the rotated and merged residuals and reflectors to update a velocity model using the acquisition geometry as based on the master grid. The earth's subsurface is imaged using the updated velocity model.