Earth Resistivity Imaging

The Earth Resistivity Imaging technique is a geophysical method that uses electrical current to define conductive and resistive areas in the subsurface. Also referred to as Electrical Resistivity Tomography (ERT), it is particularly useful in identifying underground structures, objects, pathways, fluids or zones with conductive properties that contrast with surrounding media. 2-D, 3-D, or borehole resistivity surveys can be performed depending on your need and the scope of work to be done.

Earth Resistivity Imaging is a powerful geophysical technique to identify and define:
Subsurface voids and caves
Sinkholes and other karst features
Fracture zones
Fluid pathways
Highly variable rock surfaces
Large and small scale geologic trends
Contaminant plumes
Metallic and non-metallic objects

The Earth Resistivity Imaging method employed by GeoWave Solutions, Inc. is routinely used in initial phase investigations of construction, engineering and environmental applications. This includes projects where the migration extent of leaking underground contaminants has to be determined and stability studies on dams. Because it is noninvasive and is usually not influenced by surface cultural features, it can be used practically anywhere you have access to the soil surface.

The Earth Resistivity Imaging technique typically uses an array of multiple electrodes; however, at any one given time, only four electrodes are being used simultaneously: two for current and two for potential. The resistivity of the subsurface is obtained by measuring the change in current between these four electrodes. By varying the electrode separations, different depths and locations can be sampled resulting in a profile of subsurface resistivity. Ultimately, depth of investigation for resistivity imaging is dependent on site-specific properties of the subsurface; however a general rule of thumb is depth of investigation is approximately 20% to 25% of the total line length

When numerous earth resistivity imaging arrays are positioned in close proximity to one another, it is often very helpful to be able to view the overall results in a three-dimensional field. Since subsurface features such as voids, caves, fractures, fluid pathways, and contaminant plumes are rarely two-dimensional features, a 3-D fence diagram of closely placed or overlapping two-dimensional resistivity arrays is often very helpful in characterizing the overall conditions of a project area.