1. A method for determining a velocity model, comprising: receiving a first velocity model having a first symmetry approximation of a media of a subterranean domain; receiving seismic data representing a subterranean formation; determining, by operation of a processor, a second velocity model having a second symmetry approximation of the media, the second symmetry approximation being less symmetric than the first symmetry approximation, wherein the second velocity model is determined based on an estimate of residual moveout as a function of azimuth and one or more differentials that relate one or more changes in residual moveout as a function of azimuth to one or more orthorhombic parameters; and migrating the seismic data using the second velocity model.