1. A seismic imaging method that comprises: obtaining shot gathers for a survey region; migrating shot gather data with an initial velocity model to obtain angle-domain common image gathers; determining angle-dependent travel time deviations; solving a set of tomographic equations that relate the travel time deviations to velocity model updates; applying the updates to the velocity model; and displaying a representation of the survey region to a user based at least in part on the updated velocity model.