We consider the problem of determining earth properties from seismic data, i.e. measurements with broadband acoustic waves using sources and receivers at the surface. For current data processing methods this is considered as a partially linearized inverse problem, where data is modelled by linearization about a smooth background medium, with a medium perturbation that contains only high-frequency components. Both the background, and the perturbation are to be estimated from the data. Reconstructing the high-frequency perturbation is an imaging problem, for which so called migration methods are used, that are based on geometrical wave propagation in the background medium. This talk is about establishing whether a choice of background medium is consistent with the data. A criterion for this, needed in the estimation of the background model, is given by the so called semblance principle that must be satisfied by migrated data, and that express internal consistency of redundant data, given the background medium. This talk focuses on the class of shot-geophone migration schemes. We show that shot-geophone migrated data satisfies an appropriate semblance principle, even in complex background velocities (that lead to the presence of conjugate points). The latter is not the case for binwise migration schemes, in particular Kirchhoff schemes, that form the alternative to shot-geophone migration.