Geophysics - Electrical Resistivity Method

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Electrical Resistivity Method
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Self Potential (SP)
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The resistivity imaging method uses standard arrays developed for electrical resistivity sounding and profiling techniques and modifies them to create two dimensional resistivity profiles. A line of electrodes is placed at equal intervals along the desired profile. Four electrodes are used at one time. Two inject current into the ground and two read the electrical potential between them. The resistivity meter and switch box automatically read many combinations of current and potential electrodes from short offsets to long offsets starting at one side of the electrode spread and moving toward the opposite end. The short offsets look at the shallow earth, and the longer offsets look more deeply.
Geo-Earth typically use either the dipole-dipole or the Wenner-Schlumberger array. The dipole-dipole array gives good horizontal resolution, but may have a poor signal to noise ratio (S/N) because the potential electrodes are outside of the current electrodes. The Wenner-Schlumberger array is more directed for vertical resolution, but it also gives reasonable horizontal resolution. This method has greater S/N than the dipole-dipole method because the potential electrodes are placed between the two current electrodes.
The field data contain apparent resistivity values and geometry information. These data are then inverted to produce a two dimensional (X - Z) plot of resistivity values. This resistivity inversion section is then used to interpret subsurface lithology.

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