1887
Volume 48, Issue 3
  • ISSN: 0812-3985
  • E-ISSN: 1834-7533

Abstract

[

Under certain geological conditions, low induction number electromagnetic instruments are known to produce negative apparent conductivity responses. This is particularly the case when the subsurface is characterised by highly conductive bodies. We present 3D numerical modelling results of dacite dike intrusions in Sugisawa, Akita Prefecture, Japan.

,

Under certain geological conditions, low induction number electromagnetic (LIN-EM) instruments are known to produce negative apparent conductivity () responses. This is particularly the case when the shallow subsurface is characterised by highly conductive bodies, however little attention has been given to this issue in the research literature. To analyse negative anomalies and their causative structures, we make use of a 3D integral equation forward modelling technique based on a 3D weighting function. We present 3D numerical modelling results over a volcanic tuff body intruded by several dacite dikes, in Sugisawa, Akita Prefecture, Japan. Apparent conductivity data were acquired using a Geonics EM-34–3 system in the horizontal magnetic dipole (HMD) and vertical magnetic dipole (VMD) operating modes. Our 3D model resolved the horizontal and vertical extent of the dacite dikes and also delineated a high conductive zone between the volcanic tuff and the intrusive dacite dikes. This zone is the causative structure for negative responses in the VMD data, and is interpreted to be an alteration zone. Interestingly, the negative response was absent when the instrument alignment azimuth was changed, implying an anisotropic effect on the EM signature in the study area. The true conductivity model achieved by 3D forward modelling is shown to compare favourably with the DC resistivity data acquired in the same area.

]
ASEG
Loading

Article metrics loading...

/content/journals/10.1071/EG16027
2017-09-01
2026-01-19

  • From This Site

    /content/journals/10.1071/EG16027
    dcterms_title,dcterms_subject,pub_keyword
    -contentType:Journal -contentType:Contributor -contentType:Concept -contentType:Institution
    10
    5
Loading full text...

Full text loading...

References

  1. Beamish D. 2011 Low induction number, ground conductivity meters: a correction procedure in the absence of magnetic effects: Journal of Applied Geophysics 75 244 253 10.1016/j.jappgeo.2011.07.005
    https://doi.org/10.1016/j.jappgeo.2011.07.005 [Google Scholar]
  2. Callegary J. B. Ferré T. P. A. Groom R. W. 2007 Vertical spatial sensitivity and exploration depth of low-induction-number electromagnetic-induction instruments: Vadose Zone Journal 6 158 167 10.2136/vzj2006.0120
    https://doi.org/10.2136/vzj2006.0120 [Google Scholar]
  3. Caminha-Maciel G. Figueiredo I. 2013 Error analysis in measured conductivity under low induction number approximation for electromagnetic methods: ISRN Geophysics 10.1155/2013/720839
    https://doi.org/10.1155/2013/720839 [Google Scholar]
  4. Dalan, R. A., 1995, Geophysical surveys for archaeological research electromagnetic conductivity surveys: Technical Report (unpublished), Illinois, USA.
  5. deGroot-Hedlin C. Constable S. 1990 Occam’s inversion to generate smooth, two dimensional models from magnetotelluric data: Geophysics 55 1613 1624 10.1190/1.1442813
    https://doi.org/10.1190/1.1442813 [Google Scholar]
  6. Everett, M. E., 2013, Near-surface applied geophysics: Cambridge University Press.
  7. Gómez-Treviño E. 1987 Nonlinear integral equations for electromagnetic inverse problems: Geophysics 52 1297 1302 10.1190/1.1442390
    https://doi.org/10.1190/1.1442390 [Google Scholar]
  8. Gómez-Treviño E. Esparza F. J. Méndez-Delgado S. 2002 New theoretical and practical aspects of electromagnetic soundings at low induction numbers: Geophysics 67 1441 1451 10.1190/1.1512744
    https://doi.org/10.1190/1.1512744 [Google Scholar]
  9. Hayles Geoscience Surveys Ltd, 2004, Report: EM-31 & EM-34 surveys near Springs Hill - September 1 to 5, 2004: Technical Report (unpublished), Manitoba, Canada.
  10. Kamm J. Becken M. Pedersen L. B. 2013 Inversion of slingram electromagnetic induction data using a Born approximation: Geophysics 78 E201 E212 10.1190/geo2012‑0484.1
    https://doi.org/10.1190/geo2012-0484.1 [Google Scholar]
  11. Keller, G. V., and Frischknecht, F. C., 1966, Electrical methods in geophysical prospecting: Pergamon Press, Inc.
  12. Loke, M. H., 2001, Electrical imaging surveys for environmental and engineering studies: a practical guide to 2D and 3D surveys. [Web document]. Available at http://www.geotomosoft.com/downloads.php (accessed 20 January 2016).
  13. McNeill, J. D., 1980, Electromagnetic terrain conductivity measurement at low induction numbers: Technical Note TN-6 (unpublished), Geonics Limited, Canada.
  14. McNeill, J. D., 1983, EM 34–3 survey interpretation techniques: Technical Note TN-8 (unpublished), Geonics Limited, Canada.
  15. Méndez-Delgado S. Gómez-Treviño E. Pérez-Flores M. A. 1999 Forward modeling of direct current and low frequency electromagnetic fields using integral equations: Geophysical Journal International 137 336 352 10.1046/j.1365‑246X.1999.00826.x
    https://doi.org/10.1046/j.1365-246X.1999.00826.x [Google Scholar]
  16. Mester A. van der Kruk J. Zimmermann E. Vereecken H. 2011 Quantitative two-layer conductivity inversion of multi-configuration electromagnetic induction measurements: Vadose Zone Journal 10 1319 1330 10.2136/vzj2011.0035
    https://doi.org/10.2136/vzj2011.0035 [Google Scholar]
  17. Meulenbeld, P. M., 2007, Establishing geobotanical geophysical correlations in the North-Eastern parts of South Africa for improving efficient borehole siting in difficult terrain: Ph.D. thesis, University of the Free State, Bloemfontein, South Africa.
  18. Monteiro Santos F. A. 2004 1D laterally constrained inversion of EM-34 profiling data: Journal of Applied Geophysics 56 123 134 10.1016/j.jappgeo.2004.04.005
    https://doi.org/10.1016/j.jappgeo.2004.04.005 [Google Scholar]
  19. Pérez-Flores M. A. Méndez-Delgado S. Gómez-Treviño E. 2001 Imaging of low-frequency and DC electromagnetic fields using a simple linear approximation: Geophysics 66 1067 1081 10.1190/1.1487054
    https://doi.org/10.1190/1.1487054 [Google Scholar]
  20. Pérez-Flores M. A. Antonio-Carpo R. G. Gómez-Treviño E. Ferguson I. Méndez-Delgado S. 2012 Imaging of 3D electromagnetic data at low-induction numbers: Geophysics 77 WB47 WB57 10.1190/geo2011‑0368.1
    https://doi.org/10.1190/geo2011-0368.1 [Google Scholar]
  21. Press, W. H., Teukolsky, S. A., Vetterling, W. T., and Flannery, B. P., 1992, Numerical recipes in C: the art of scientific computing (2nd edition): Cambridge University Press.
  22. Romberg W. 1955 Vereinfachte numerische Integration: Det Kongelige Norske Videnskabers Selskab Forhandlinger (Trondheim) 28 30 36
    [Google Scholar]
  23. Sasaki Y. 1989 Two-dimensional joint inversion of magnetotelluric and dipole-dipole resistivity data: Geophysics 54 254 262 10.1190/1.1442649
    https://doi.org/10.1190/1.1442649 [Google Scholar]
  24. Sasaki Y. 2001 Full 3D inversion of electromagnetic data on PC: Journal of Applied Geophysics 46 45 54 10.1016/S0926‑9851(00)00038‑0
    https://doi.org/10.1016/S0926-9851(00)00038-0 [Google Scholar]
  25. Sasaki, D., 2007, Electrical conductivity structure analysis by electromagnetic survey: M.Sc. thesis, Akita University [in Japanese with English abstract].
  26. Sasaki Y. Meju M. A. 2006 A multidimensional horizontal-loop controlled-source electromagnetic inversion method and its use to characterize heterogeneity in aquiferous fractured crystalline rocks: Geophysical Journal International 166 59 66 10.1111/j.1365‑246X.2006.02957.x
    https://doi.org/10.1111/j.1365-246X.2006.02957.x [Google Scholar]
  27. Song Y. Kim J. H. 2008 An efficient 2.5D inversion of loop-loop electromagnetic data: Exploration Geophysics 39 68 77 10.1071/EG08007
    https://doi.org/10.1071/EG08007 [Google Scholar]
  28. Spies B. R. 1989 Depth of investigation in electromagnetic sounding methods: Geophysics 54 872 888 10.1190/1.1442716
    https://doi.org/10.1190/1.1442716 [Google Scholar]
  29. Wait, J. R., 1982, Geo-electromagnetism: Academic Press.
  30. Wessel P. Smith W. H. F. Scharroo R. Luis J. F. Wobbe F. 2013 Generic mapping tools: improved version released: EOS 94 409 410 10.1002/2013EO450001
    https://doi.org/10.1002/2013EO450001 [Google Scholar]
  31. Zhdanov M. S. Fang S. 1996 Quasi-linear approximation in 3D electromagnetic modeling: Geophysics 61 646 665 10.1190/1.1443994
    https://doi.org/10.1190/1.1443994 [Google Scholar]
/content/journals/10.1071/EG16027
Loading
3D numerical modelling of negative apparent conductivity anomalies in loop-loop electromagnetic measurements: a case study at a dacite intrusion in Sugisawa, Akita Prefecture, Japan
Exploration Geophysics 48, 177 (2017); https://doi.org/10.1071/EG16027
/content/journals/10.1071/EG16027
/content/journals/10.1071/EG16027
Loading

Data & Media loading...

  • Article Type: Research Article
Keyword(s): electromagnetics, forward modelling, negative apparent conductivity, weighting function.

Most Cited This Month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error