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VLF ANOMALIES FROM A PERFECTLY CONDUCTING HALF PLANE BELOW AN OVERBURDEN *
Author(s) -
OLSSON O.
Publication year - 1980
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/j.1365-2478.1980.tb01236.x
Subject(s) - overburden , anomaly (physics) , conductor , geology , gemology , regional geology , plane (geometry) , attenuation , economic geology , electrical resistivity and conductivity , conductivity , environmental geology , geophysics , mineralogy , engineering geology , geometry , seismology , tectonics , optics , physics , geotechnical engineering , condensed matter physics , mathematics , metamorphic petrology , quantum mechanics , volcanism , telmatology
A bstract A theoretical solution to the electromagnetic problem of a perfectly conducting half plane below a conducting overburden has been obtained. The VLF anomalies have been computed for different overburden conductivity and thickness and also for different dip angles of the half plane. In the computations the contribution to the secondary magnetic field from the electric Hertz potential has been neglected. The anomaly curves which are displayed as EM 16 readings, show a fairly complicated behaviour. This is mainly due to the phase shift and attenuation of the field caused by the conductivity of the overburden and the host rock. From the anomaly curves it is possible to define the apparent depth to the top of the conductor as the distance between the peak value and the cross‐over of the real component. The apparent depth is usually larger than the actual depth, but it is possible to determine the actual depth to the conductor from the relation between the peak‐to‐peak anomaly and the apparent depth. When the peak‐to‐peak anomaly is fairly large, it is also possible to make estimates of the dip angle. However, a complete set of master curves will be a necessary tool for interpretation of VLF data when there is need to obtain more accurate estimates of the half plane parameters. In a specific case the theoretical calculations are shown to be in good agreement with measured data.