Formation absorption seismic method

A seismic prospecting method for finding zones of anomalous absorption of seismic waves between pairs of refractive layers in subsurface formations, comprising:

• a. locating a number of seismic wave detectors in a plurality of groups in a first spread at least near the surface of the earth;
• b. initiating seismic waves at a first source location near the surface of the earth a distance L.sub.1 from one end of said spread, and making a reproducible record of at least the amplitude of initially received refracted seismic waves at said plurality of groups of detectors from this initiation;
• c. repeating step b for seismic waves initiated at a distance L.sub.2 from said one end of said spread, L.sub.2 being at least substantially greater than L.sub.1 ;
• d. repeating step b for seismic waves initiated substantially at a distance L.sub.1 from the opposite end of said first spread;
• e. repeating step b for seismic waves initiated at least substantially at a distance L.sub.2 from said opposite end of said first spread;
• f. locating a second spread of detectors in which at least the majority of said groups of detectors have not been moved, but at least one such group of detectors in said second spread is at a new location at an end of said second spread;
• g. repeating step b, c, d and e for the detector groups forming said second spread, whereby the relative amplitudes of said initially received seismic waves corrected for size of shot, range and group may be determined for refracted waves received at each group for seismic wave initiations at the various locations L.sub.2, and h. plotting on a cross-section map on up-coming lines representing at least approximately the up-coming paths of refracted waves to the various detector group locations, the corresponding value of said relative corrected amplitudes of said initially received seismic waves at said various detector groups, so that zones of anomalous absorption of refracted waves may be ascertained.