1887
Volume 66, Issue 2
  • E-ISSN: 1365-2478

Abstract

ABSTRACT

We present a simple and feasible approach to analyse and identify two‐dimensional effects in central loop transient electromagnetic sounding data and the correspondingly derived quasi two‐dimensional conductivity models. The proposed strategy is particularly useful in minimising interpretation errors. It is based on the calculation of a semi‐synthetic transient electromagnetic tipper at each sounding and for each observational transient time point. The semi‐synthetic transient electromagnetic tipper is derived from the measured vertical component of the induced voltage and the synthetically calculated horizontal component. The approach is computationally inexpensive and involves one two‐dimensional forward calculation of an obtained quasi two‐dimensional conductivity section. Based on a synthetic example, we demonstrate that the transient electromagnetic tipper approach is applicable in identifying which transient data points and which corresponding zones in a derived quasi two‐dimensional subsurface model are affected by two‐dimensional inhomogeneities. The one‐dimensional inversion of such data leads to false models. An application of the semi‐synthetic transient electromagnetic tipper to field data from the Azraq basin in Jordan reveals that, in total, eight of 80 investigated soundings are affected by two‐dimensional structures although the field data can be fitted optimally using one‐dimensional inversion techniques. The largest semi‐synthetic tipper response occurs in a 300 m‐wide region around a strong lateral resistivity contrast. The approach is useful for analysing structural features in derived quasi two‐dimensional sections and for qualitatively investigating how these features affect the transient response. To avoid misinterpretation, these identified zones corresponding to large tipper values are excluded from the interpretation of a quasi two‐dimensional conductivity model. Based on the semi‐synthetic study, we also demonstrate that a quantitative interpretation of the horizontal voltage response (e.g. by inversion) is usually not feasible as it requires the exact sensor position to be known. Although a tipper derived purely from field data is useful as a qualitative tool for identifying two‐dimensional distortion effects, it is only feasible if the sensor setup is sufficiently accurate. Our proposed semi‐synthetic transient electromagnetic tipper approach is particularly feasible as an approach if no horizontal components are recorded or if the sensor setup in the field is not sufficiently accurate.

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2017-05-05
2020-05-30
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References

  1. AukenE. and ChristensenA.V.2004. Layered and laterally constrained 2D inversion of resistivity data. Geophysics69, 752–761.
    [Google Scholar]
  2. AukenE., PellerinL., ChristensenN.B. and SørensenK.2006. A survey of current trends in near‐surface electrical and electromagnetic methods. Geophysics71(5), 249–260.
    [Google Scholar]
  3. ConstableS.C., ParkerR.L. and ConstableC.G.1987. Occam's inversion: a practical algorithm for generating smooth models from EM sounding data. Geophysics52(3), 289–300.
    [Google Scholar]
  4. DanielsenJ.E., AukenE., JørgensenF., SøndergaardV. and SørensenK.I.2003. The application of the transient electromagnetic method in hydrogeophysical surveys. Journal of Applied Geophysics53(4), 181–198.
    [Google Scholar]
  5. DruskinV.L. and KnizhnermannL.A.1988. A spektral semi‐discrete method for the numerical solution of 3D nonstationary problems in electrical prospecting. Physics of the Solid Earth24, 641–648.
    [Google Scholar]
  6. DruskinV.L. and KnizhnermannL.A.1994. Spectral approach to solving three‐dimensional Maxwell's diffusion equations in the time and frequency domains. Radio Science29(4), 937–953.
    [Google Scholar]
  7. DruskinV.L. and KnizhnermannL.A.1999. New spectral Lanczos decomposition method for induction modeling in arbitrary 3‐D geometry. Geophysics64(3), 701–706.
    [Google Scholar]
  8. EverettM.E.2011. Theoretical developments in electromagnetic induction geophysics with selected applications in the near surface. Surveys in Geophysics33(1), 29–63.
    [Google Scholar]
  9. FittermanD.V. and StewartM.T.1986. Transient electromagnetic sounding for groundwater. Geophysics51(4), 995–1005.
    [Google Scholar]
  10. GoldmanM. and NeubauerF.M.1994. Groundwater exploration using integrated geophysical techniques. Surveys in Geophysics15, 331–361.
    [Google Scholar]
  11. GoldmanM., TabarovskytL. and RabinovichM.1994. On the influence of 3D structures in the interpretation of transient electromagnetic sounding data. Geophysics59(6), 889–901.
    [Google Scholar]
  12. JørgensenF., SandersenP.B. and AukenE.2003. Imaging buried Quaternary valleys using the transient electromagnetic method. Journal of Applied Geophysics53(4), 199–213.
    [Google Scholar]
  13. KochO., HelwigS., TezkanB. and the DESERT group2003. Strategien zur Erkundung einer schmalen vertikalen Leitfhigkeitsanomalie mit TEM‐Methoden. In: Protokoll über das 20. Kolloquium für Elektromagnetische Tiefenforschung. Deutsche Geophysikalische Gesellschaft.
  14. NabighianM.N.1979. Quasi‐static transient response of a conducting half‐space‐An approximate representation. Geophysics44(10), 1700–1705.
    [Google Scholar]
  15. NabighianM.N. and MacnaeJ.C.1991. Time domain electromagnetic prospecting methods. In: Electromagnetic Methods in Applied Geophysics, Vol. 2, Ch. 6 (ed M.N.Nabighian ). Society of Exploration Geophysicists.
    [Google Scholar]
  16. NewmanG.A., AndersonW.L. and HohmannG.W.1987. Interpretation of transient electromagnetic soundings over three‐dimensional structures for the central‐loop configuration. Geophysical Journal of the Royal Astronimical Society89, 889–914.
    [Google Scholar]
  17. PellerinL.2002. Applications of electrical and electromagnetic methods for environmental and geotechnical investigations. Surveys in Geophysics23(2‐3), 101–132.
    [Google Scholar]
  18. RödderA. and TezkanB.2013. A 3D resistivity model derived from the transient electromagnetic data observed on the Araba fault, Jordan. Journal of Applied Geophysics88, 42–51.
    [Google Scholar]
  19. SpiesB.R. and FrischknechtF.C.1991. Electromagnetic sounding. In: Electromagnetic Methods in Applied Geophysics, Vol. 2, Ch. 5 (ed M.N.Nabighian ). Society of Exploration Geophysicists.
    [Google Scholar]
  20. TezkanB.1999. A review of environmental applications of quasi‐stationary electromagnetic techniques. Surveys in Geophysics20, 279–308.
    [Google Scholar]
  21. ViezzoliA., ChristensenA., AukenE. and SørensenK.2008. Quasi‐3D modeling of airborne TEM data by spatially constrained inversion. Geophysics73, 105–113.
    [Google Scholar]
  22. VozoffK.1991. The magnetotellurik method. In: Electromagnetic Methods in Applied Geophysics, Vol. 2, Ch. 8 (ed M.N.Nabighian ). Society of Exploration Geophysicists.
    [Google Scholar]
  23. YogeshwarP. and TezkanB.2017. Two‐dimensional basement modeling of central loop transient electromagnetic data from the central Azraq basin area, Jordan. Journal of Applied Geophysics136, 198–2010.
    [Google Scholar]
  24. YogeshwarP., TezkanB. and HaroonA.2013. Investigation of the Azraq sedimentary basin, Jordan using integrated geoelectrical and electromagnetic techniques. Near Surface Geophysics11, 283–291.
    [Google Scholar]
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  • Article Type: Research Article
Keyword(s): 2D FD modelling , 2D structures and Transient electromagnetic method
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