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The Electromagnetic Azimuthal Resistivity Method
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 9th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Apr 1996, cp-205-00004
Abstract
Pumping ground water from a fractured rock aquifer commonly leads to preferential drawdown<br>controlled by bedrock fracture orientation. The azimuthal resistivity method has previously been used to detect<br>this fracture orientation in covered areas, which has led to a determination of the principal directions of<br>transmissivity by geophysical means. However, the azimuthal resistivity method often requires a large amount<br>of space, free from cultural interference. In additon, data collection can be both labor intensive and time<br>consuming.<br>In this paper, we describe the collection of azimuthal resistivity data using electromagnetic methods.<br>Commonly available terrain conductivity instruments can be used in the horizontal coplanar (vertical dipole)<br>configuration, and data collected in an azimuthal array. Field examples using this system are presented showing<br>empirical comparisons with azimuthal resistivity data, and both geologic and hydrogeologic data sets. Data<br>collection efficiency is increased six-fold by using electromagnetic methods in this application, compared to the<br>azimuthal resistivity method. Disadvantages of the resistivity method, such as high electrode contact resistance<br>and large spread lengths necessary for relatively shallow penetration, are avoided or lessened by the use of<br>electromagnetic methods.