1887
Volume 41 Number 8
  • E-ISSN: 1365-2478

Abstract

A

The VLF filtering technique of Karous and Hjelt has been applied to fixed‐loop step‐response transient electromagnetic data. This allows the data measured in each channel to be converted to an equivalent current‐density pseudosection.

For a conductive half‐space, the maximum value of the equivalent current density starts near the transmitter loop and migrates outwards as a function of delay time. The rate of migration tends to increase as a function of delay time, with the increase being faster for a surficial conductive layer than it is for a half‐space.

Theoretical and field examples show that the currents tend to be more persistent in the relatively conductive areas, so that a pseudosection which is the average of the current densities at all delay times will highlight the more conductive zones.

In resistive ground, it is not so critical to average the pseudosections as a particular delay time may give a better idea of the conductivity structure. For example, the latest possible delay time will reveal the most conductive features.

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2006-04-27
2020-08-05
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References

  1. Fraser, D.C.1969. Contouring of VLF‐EM data. Geophysics34, 977–991.
    [Google Scholar]
  2. Karous, M. and Hjelt, S.E.1983. Linear filtering of VLF dip‐angle measurements. Geophysical Prospecting31, 782–794.
    [Google Scholar]
  3. Ogilvy, R.D. and Lee, A.C.1991. Interpretation of VLF‐EM in‐phase data using current density pseudosections. Geophysical Prospecting39, 567–580.
    [Google Scholar]
  4. Polzer, B.D., Macnae, J.C., Miura, Y. and Takasugi, S.1990. Stripping cultural conductor responses from EM data. 60th SEG meeting, San Francisco, Expanded Abstracts, 487–490.
  5. Raiche, A.P. and Sugeng, F.1989. Predicting the transient EM response of complex structures using the compact finite element method. Exploration Geophysics20, 51–55.
    [Google Scholar]
  6. Smith, R.S. and West, G.F.1987. Electromagnetic induction in an inhomogeneous conductive thin sheet. Geophysics52, 1677–1688.
    [Google Scholar]
  7. West, G.F., Macnae, J.C. and Lamontagne, Y.1984. A time‐domain EM system measuring the step response of the ground. Geophysics49, 1010–1026.
    [Google Scholar]
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