Discriminating physical and non-physical diffracted energy in source–receiver interferometry

Abstract

SUMMARY We show how physical and non-physical diffracted waves can be discriminated in source– receiver interferometry (SRI), a wavefield interferometric method that constructs Green’s functions between any source–receiver pair. These can be estimated by convolution and crosscorrelation of wavefields propagating to or from other sources or receivers. SRI has been observed to work surprisingly well in practical applications when theoretical requirements (e.g. complete enclosing boundaries of other sources and receivers) are contravened as is standard in practical applications. As a partial explanation to this, it has been demonstrated previouslythatSRIforsinglediffractorproblemsproducescorrectGreen’sfunctionsestimates without requiring wavefields to be generated around specific stationary-phase points in space (as is required by other forms of interferometry). In this paper, we show that also for multiplediffractorproblems,anyboundarysource–receiverpairproducesstationary,correctkinematics for singly and multiply diffracted waves. However, when multiple diffractors are present, non-physical artefacts are produced in Green’s functions estimated by SRI with incomplete boundaries. We introduce a purely data-driven algorithm that allows traveltimes of any order ofphysical, diffractedwaves tobepredicted. Thisreduces ambiguity ininterpreting wavefields generated using SRI with only partial boundaries: this also permits spurious or non-physical energy in the constructed Green’s functions to be identified and either interpreted or ignored.