Why Building Adequate Depth Velocity Model by Seismic Data is not Always Successful?

It is shown, that for getting RMS velocities with enough accuracy diffraction approach is strongly recommended in comparison with methods such as CMP, DMO, MF, CRS. Diffraction approach is realized in Kirchhoff migration, PRO migration and getting PRO time sections. For Kirchhoff migration there is dependence of definition velocities by accumulation maximum from the reflectors curvature. Curvatures of PRO operators are massively more on the average, so there is no such dependence for PRO method, so the method allows us to define adequate for geology interval velocities.