Seismic interferometry by tangent-phase correction

We present a modified interferometry method based on local tangent-phase analysis, which corrects the cross-correlated data before summation. The approach makes it possible to synthesize virtual signals usually vanishing in the conventional seismic interferometry summation. For a given pair of receivers and a set of different source positions, a plurality of virtual traces is obtained at new stationary projected points located along the signal wavefronts passing through the real reference receiver. The position of the projected points is estimated by minimizing travel times using wavefront constraint and correlation-signal tangent information. The method uses mixed processing, which is partially based on velocity-model knowledge and on data-based blind interferometry. The approach can be used for selected events, including reflections with different stationary conditions and projected points with respect to those of the direct arrivals, to extend the interferometry representation in seismic exploration data where conventional illumination coverage is not sufficient to obtain the stationary-phase condition. We discuss possible applications in crosswell geometry with a velocity anomaly and a time lapse.