THREE-DIMENSIONAL SUBSURFACE DELINEATION VIA A NOVEL METHOD FOR DETERMINING THE SUBSURFACE ELECTRICAL PROFILE

摘要

The combination of a standard experimental procedure (four-probe electrical resistivity), a novel analytical technique (probabilistic potential theory), and a powerful inversion algorithm (optimization/generalized linear inverse) is proposed as a method for determining the subsurface electrical profile. Fourprobe electrical measurements can yield electrical profiles which, in the light of known geologic information about the site, can be related directly to subsurface structure. However, the reduction of field data from such measurements heretofore has generally been successful only for the mathematically nice situations (e. g. , horizontal or vertical stratification). For the more complicated case of general subsurface structure, the presently available analytical methods rapidly become unwieldy, computer, limited, or cost-ineffective. The analytical procedure proposed here should overcome these limitations and permit the efficient solution of complicated problems of subsurface structure. It is proposed that the feasibility of the procedure be tested by analysis of field experiments in conjunction with scalemodel laboratory experiments to validate the algorithms for general structure. The procedure should have great practical value in a wide variety of applications:hydrology, location and definition of the shape and extent of underground resources (e. g. , geothermal reservoirs, ore bodies, or deposits of coal, sand, or gravel), faultline definition, and monitoring of changes in subsurface conditions (e. g. , as in earthquake studies, in situ coal gasification, and burn-front studies of oil-shale gasification).