Abstract
AbstractThe measurement of wavetilt is diagnostic for determining the electrical characteristics of the upper layers of the ground at VLF and LF frequency ranges. Theoretical and field studies have indicated that electric wavetilt using the transverse magnetic (TM) waves detects lateral inhomogeneities virtually instantly as abrupt changes in electrical properties are encountered. Theoretical studies have also indicated that magnetic wavetilt measurements using transverse electric (TE) waves are superior to electric wavetilts for such purposes.An experimental survey was conducted at two locations near Atikokan, Ontario, to verify the theoretical predictions. The survey area, forming a part of a large granitic pluton, was mapped earlier by various geophysical techniques, including the ground VLF‐EM method, to detect weak conductors formed either by the presence of fractures in the bedrock filled with water and/or clay, or overburden filling bedrock depressions.A small, multi‐turn, horizontal loop was used during the survey as the transmitter to generate TE waves at eleven frequencies from 10.7 to 58.5 kHz. The magnetic wavetilt measurements detected all previously known conductors at the two locations. In addition, the survey detected several weak conductors that were missed by the VLF survey. Thus, the survey indicated the usefulness of magnetic wavetilt results for detection of weak conductors at shallow depths, which may have application in engineering geophysical surveys. The multi‐frequency wavetilt data also provided some indications of the depth and depth extent of such conductors.
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