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Subsurface Exploration in Alluvial Terrain by Surface Geophysical Methods

Abstract : Field tests were conducted at several sites in Louisiana to determine the effectiveness of two geophysical tools for detecting and locating subsurface geological features in alluvial terrain. The hammer seismic refraction technique, using a hammer source and portable seismograph, and the surface electrical resistivity method, using a D.C.-powered resistivity meter and current source, were investigated. Seismic refraction lines and resistivity soundings and profiles were run concurrently at each site. Boring control was used where available to aid in interpretation of the geophysical data. The resistivity profiling (fixed electrode spacing) technique was the most successful of the three methods, detecting or locating the targeted geologic feature at three of the four sites tested. The resistivity sounding (expanding electrode spacing) technique delineated shallow features but was ineffective at depth. The hammer seismic technique also achieved only limited success at depth, attributed primarily to attentuation of the seismic signals by loose near-surface materials. Surveys were precluded at one site by the presence of certain man-made features that interfered with the collection of usable data.