Seismic holography

Claim 1

A process for seismic holography comprising a. transmitting coherent acoustical energy into the earth at a first surface location, b. receiving seismic signals with areal detector means at a plurality of detector locations remote from said first location, c. obtaining a reference signal by detecting transmitted acoustical energy at a point adjacent said first location, d. selectively time delaying said reference signal with respect to each seismic signal with which it is to be combined in order to achieve maximum interference, e. amplifying said reference signal to a predetermined level relative to each seismic signal to accomplish field of depth focusing, f. combining each of said seismic signals with the reference signal as modified in steps (d) and (e) to produce a plurality of corresponding interference signals, g. modulating the illuminous intensity of a point source of light with each of said interference signals, h. forming a photographic record of the light output resulting from the modulations such that a plurality of spot exposures are formed having the same geometrical relation as the detector locations where the seismic signals were derived, i. scaling said photographic record in order to reduce it to dimensions compatible for reconstruction at optical wavelengths, and j. illuminating the hologram thus obtained with coherent light so that a holographic image is formed of the earth''s subsurface.