Time-shift imaging condition

We derive a new generalized imaging condition based on time shifts between source and receiver wavefields. This imaging condition contrasts with other imaging techniques requiring space shifts between the two wavefields. This imaging condition is applicable to both Kirchhoff and wave-equation migrations. The transformation allows us to generate common-image gathers presented as function of either time-shift or pseudo-angle at every location in space. Inaccurate migration velocity is revealed by common-image gathers with non-flat events.