Electrical resistivity tomography as a method for imaging the shallow subsurface in an investigation of weathered rock and large mass movements
Wylie, William James
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Two dimensional electrical resistivity tomography was used to image a large, slow moving landslide in Macon County, North Carolina as well as the soil-bedrock transition zone of the Inner Piedmont near Athens, Georgia. Apparent resistivity data were inverted using damped least squares to derive models of resistivity structure of the shallow subsurface. For the landslide investigation, data were acquired along three profiles oriented perpendicular to movement using a four-channel resistivity meter. Maximum depth of imaging was 15 meters. The models show well-drained material with overall resistivity decreasing towards lower elevations. Large areas of low resistivity within the landslide were determined to be preferential pathways for water drainage downslope. Small wavelength anomalies occur in the non-mobile material as pockets of high resistivity at depth, interpreted as large boulders and compacted material. For the Inner Piedmont investigation, data were acquired along three E-W profiles overlying dipping bedrock. A value of 200 ohm-m was interpreted as bedrock and is seen as a sharp contrast to the overlying soil and saprolite. The topography of the area does not mimic the bedrock structure. No evidence is seen at the surface of a steep drop-off in the bedrock at roughly 90 meters along each line.