1887
Volume 19, Issue 3
  • ISSN: 0812-3985
  • E-ISSN: 1834-7533

Abstract

Electromagnetic transients measured with coincident transmitter and receiver loops are usually positive at all delay times. The response occasionally switches to negative at late times; a possible cause of which is an induced electrical polarization. Unfortunately, it is not possible to explain the negative transients with a half-space or a single bedrock conductor unless the polarizability of the model is unrealistically large. A negative response can be obtained with a realistic polarizability if the coincident-loop response of a body is large and positive at early time and decreases very rapidly. The current associated with the positive response polarizes the body: the larger the positive response, the greater the polarization. However, the positive response must also decay away rapidly, so that the smaller response associated with the polarization will be observed as a negative transient at late time. A body with such a response is a conductive overburden. Because the large early-time currents induced in an overburden flow close to the transmitter loop, the most significant polarization will occur here. When this polarization is large, the sign of the vertical-field response will be reversed when the receiver is inside, or coincident with, the transmitter loop. If the polarization is small, the distortion of the response near the wire is similar to what is termed ‘the loop effect’. These abnormal TEM responses can be modelled with a weakly polarizable overburden, suggesting that polarization effects are a plausible explanation.

© 1988 ASEG
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1988-06-01
2026-01-23

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References

  1. Anderson, W. L. (1982) — ‘Fast Hankel transforms using related and lagged convolutions’, ACM Trans, on Math. Software, 8, 344–368.
  2. Asten, M. W. and Price, D. G. (1985) — ‘Transient EM sounding by the in/out-loop method’, Paper presented at the 4th Geophysical Conference and Exhibition of the Australian Society of Exploration Geophysicists’, Sydney, September 1985. Published as an expanded abstract in Exploration Geophysics16, 165–168.
  3. Astrakhantsev, G. V., Gavrilova, I. E., Shuravleva, R. B. and Ulitin, R. V. (1975) — ‘Effect of the polarizing properties of rocks on the build-up of the electromagnetic field’, Physics of the Solid Earth, (an English edition of a Soviet journal, published by the American Geophysical Union, December, 1975), 11, 330–333.
  4. Bhattacharyya, B. K. (1964) — ‘Electromagnetic fields of a small loop antenna on the surface of a polarizable medium’, Geophysics29, 814–831.
  5. Buselli, G. (1982) — ‘The effect of near surface superparamagnetic material on electromagnetic transients’, Geophysics47, 1315–1324.
  6. Buselli, G. and O’Neill, B. (1977) — ‘SIROTEM: a new portable instrument for multichannel transient electromagnetic measurements’, Bull. of the Aust. Soc. Explor. Geophys. 8, 82–87.
  7. Chave, A. D. (1983) — ‘Numerical integration of related Hankel transforms by quadrature and continued fraction expansion’, Geophysics48, 1671–1686.
  8. Dias, C. A. (1968), ‘A non-grounded method for measuring induced polarization and conductivity’, Unpub. Ph.D thesis, University of California, Berkeley, p260.
  9. Edwards, R. N. and Cheesman, S. J. (1987) — ‘Two-dimensional modelling of a towed transient magnetic dipole-dipole sea floor EM system’, J. Geophys. 61, 110–121.
  10. Elliott, P. J. (1987) — ‘Negative SIROTEM anomalies — case studies’, Paper presented at the 5th Geophysical Conference and Exhibition of the Australian Society of Exploration Geophysicists, Perth, February 1987. Published as an expanded abstract in Exploration Geophysics18, 42–47.
  11. Flis, M. F. (1987) — ‘IP effects in 3-D TEM data — theory and case histories’, Paper presented at the 5th Geophysical Conference and Exhibition of the Australian Society of Exploration Geophysicists, Perth, February 1987. Published as an expanded abstract in Exploration Geophysics18, 55–58.
  12. Grant, F. S. and West, G. F. (1965), Interpretation theory in applied geophysics, McGraw-Hill, N.Y. p584.
  13. Guptasarma, D. (1984) — ‘Positivity of the coincident-loop transient electromagnetic response’, Geophysics49, 194.
  14. Hohmann, G. W., Kintzinger, P. R., Van Voorhis, G. D. and Ward, S. H. (1970) — ‘Evaluation of the measurement of induced electrical polarization with an inductive system’, Geophysics 35, 901-915. See also discussion in Geophysics36, 427–429.
  15. Hoversten, G. M. and Morrison, H. F. (1982) — ‘Transient fields of a current loop source above a layered earth’, Geophysics47, 1068–1077.
  16. Johansen, H. K. and Sorensen, K. (1979) — ‘Fast Hankel transforms’, Geophys. Prosp. 27, 876–901.
  17. Kamenetskii, F. M. and Timofeev, V. M. (1984) — ‘The possibility of separating induction and polarization effects’, Physics of the Solid Earth, (an English edition of a Soviet journal, published by the American Geophysical Union, July, 1985) 20, 950–954.
  18. Knight, J. H. and Raiche, A. P. (1982) — ‘Transient electromagnetic calculations using the Gaver-Stehfest inverse Laplace transform method’, Geophysics47, 47–50.
  19. Lee, T. (1975) — ‘Sign reversals in the transient method of electrical prospecting (one loop version)’, Geophys. Prosp. 23, 653–662. 653–662.
  20. Lee, T. (1981) — ‘Transient electromagnetic response of a polarizable ground’, Geophysics46, 1037–1041.
  21. Lee, T. (1982) — ‘Asymptotic expansions for transient electromagnetic fields’, Geophysics47, 38–46.
  22. Lewis, R. J. G. and Lee, T. (1984) — ‘The detection of induced polarization with a transient electromagnetic system’, IEEE trans. on Geosciences and Remote SensingGE-22, 69–80.
  23. Molchanov, A. A., Sidorov, V. A., Nikolayev, Yu. V. and Yakhin, A. M. (1984) — ‘New types of transient processes in electromagnetic sounding’, Physics of the Solid Earth, (an English edition of a Soviet journal, published by the American Geophysical Union, August, 1984), 20, 76–79.
  24. Morrison, H. F., Phillips, R. J. and O’Brien, D. P. (1969) — ‘Quantitative Interpretation of transient electromagnetic fields over a layered half-space’, Geophys. Prosp. 17, 82–101.
  25. Nabighian, M. N. (1979) — ‘Quasi-static transient response of a conductive half-space — An approximate representation’, Geophysics44, 1700–1705.
  26. Ohloeft, G. R. (1985) — ‘Low-frequency electrical properties’, Geophysics50, 2492–2503.
  27. Pelton, W. H. (1977) — ‘Interpretation of induced polarization and resistivity data’, — Ph.D thesis University of Utah, Salt Lake City, p255.
  28. Pelton, W. H., Ward, S. H., Hallof, P. G., Sill, W. R. and Nelson, P. H. (1978) — ‘Mineral discrimination and removal of inductive coupling with multifrequency IP’, Geophysics43, 588–609.
  29. Raiche, A. P. (1983) — ‘Negative transient voltage and magnetic field responses for a half-space with a Cole-Cole impedance’, Geophysics48, 790–791.
  30. Raiche, A. R, Russell, L. A., Clark, P. J. and Smith, R. J. (1985) — ‘The use of Cole-Cole impedances to interpret the TEM response of layered earths’, Paper presented at the 4th Geophysical Conference and Exhibition of the Australian Society of Exploration Geophysicists, Sydney, September 1985. Published as an expanded abstract in Exploration Geophysics16, 271–273.
  31. Scott, W. J. and West, G. F. (1969) — ‘Induced polarization of synthetic, high-resistivity rocks containing disseminated sulphides’, Geophysics34, 87–100.
  32. Seigel, H. O. (1959) — ‘Mathematical formulation and type curves for induced polarization’, Geophysics24, 547–565.
  33. Sidorov, V. A. and Yakhin, A. M. (1979) — ‘Induced polarization in rocks with inductive excitation’, Physics of the Solid Earth, (an English edition of a Soviet journal, published by the American Geophysical Union, June, 1980), 15, 810–814.
  34. Smith, R. S. and West, G. F. (1987) — ‘Electromagnetic induction in an inhomogeneous conductive thin sheet’, Geophysics52, 1677–1688.
  35. Smith, R. S. and West, G. F. (1988) — ‘Inductive interaction between polarizable conductors: An explanation of a negative coincident-loop TEM response’, Geophysics53, 677–690.
  36. Smith, R. S., Walker, P. W., Polzer, B. D. and West, G. F. (1988) — ‘The time-domain electromagnetic response of polarizable bodies: An approximate convolution algorithm’, Geophys. Prosp. 36, 772–785
  37. Sneddon, I. N. (1951), Fourier transforms, McGraw-Hill, N.Y., p542.
  38. Spies, B. R. (1980a) — ‘A field occurrence of sign reversals with the transient electromagnetic method’, Geophys. Prosp. 28, 620–632.
  39. Spies, B. R. (1980b) — ‘Results of experiment and test TEM surveys, Elura deposit, Cobar NSW’, in D. W. Emersen (ed.), The Geophysics of the Elura Orebody, Cobar NSW, Bull. Aust. Soc. Explor. Geophys. 11, 147–152.
  40. Stehfest, H. (1970a) — ‘Algorithm 368, Numerical inversion of Laplace transforms’, Comm. Assn. Comp. Mach. 13, 47–49.
  41. Stehfest, H (1970b) — ‘Remark on Algorithm 368, Numerical inversion of Laplace transforms’, Comm. Assn. Comp. Mach. 13, 624.
  42. Vacquier, V., Holmes, C. R., Kintzinger, P. R. and Lavergne, M. (1957) — ‘Prospecting for ground water by induced electrical polarization’, Geophysics22, 660–687.
  43. Villinger, H. (1985) — ‘Solving cylindrical geothermal problems using the Gaver-Stehfest inverse Laplace transform’, Geophysics50, 1581–1587.
  44. Wait, J. R. (1982), Geo-electromagnetism, Academic Press N.Y., p268.
  45. Wait, J. R. and Debroux, P. (1984) — ‘Induced polarization in electromagnetic inductive schemes’, Geophys. Prosp. 32, 1147–1154.
  46. Weidelt, P. (1982) — ‘Response characteristics of coincident-loop transient electromagnetic systems’, Geophysics47, 1325–1330.
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  • Article Type: Research Article
Keyword(s): negative smoke rings; overburden response; polarization current; polarization effects in TEM; SIROTEM.; TEM negative transients; the loop effect; transient electromagnetics

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