Abstract
An interferometric form of Fermat's principle is derived that allows for high-resolution estimation of the velocity distribution between deep interfaces. The data consist of reflection traveltimes from two deeply buried interfaces A and B recorded by sources and caused by receivers at the surface. Fermat's interferometric principle is then used to kinematically redatum the surface sources and receivers to interface A so that the associated reflection times correspond to localized transit times between the A and B interfaces. The velocity model above interface A does not need to be known, so the distorting effects of the overburden and statics are eliminated by this target-oriented approach. Interferometric target-oriented tomography promises to enhance the resolution of whole-earth and exploration tomograms.