Volume 44 Number 6
  • E-ISSN: 1365-2478



A case history is presented where electromagnetic (EM) methods were applied as a complement to seismic, for structural mapping in basin‐and‐range‐like geology: 366 five‐component magnetotelluric (MT) soundings were carried out together with 331 transient soundings (TDEM) along seismic lines.

Due to high structural complexity, seismic shows a number of limitations. For the same reasons, MT is highly perturbed and three specific interpretation techniques were comprehensively applied:

1. a classical correction of static effect using TDEM sounding, to determine the high‐frequency nondistorted apparent resistivities and thus the corrected tensor;

2. a so‐called regional correction based upon the same concept as the static effect, to transform distorted resistivity curves due to the horst/graben situation into plausible 1D curves, through the use of nomograms built for 2D H‐polarization situations;

3. a stripping technique which made it possible to map areas where a deep conductive Mesozoic shale was present below carbonates, at a depth of 3 km.

After the best MT interpretation was obtained along each line, it was integrated with seismic and with the results from two boreholes. A crude empirical law relating resistivity and acoustic velocity was established and the MT horizons were plotted on the two‐way traveltime seismic sections.

The final integrated cross‐sections obtained are undoubtedly of greater use to the explorationist than the initial seismic sections alone and two wells were accurately predicted.


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  1. AndrieuxP. and WightmanW.E.1984. The so‐called static corrections in magnetotelluric measurements. 54th SEG meeting, Atlanta, Expanded Abstracts, 43–44.
  2. ChaveA.D. and Torquil SmithJ.1994. On electric and magnetic galvanic distortion tensor decompositions. Journal of Geophysical Research99B3, 4669–4682.
    [Google Scholar]
  3. GolubG.H. and ReinschC.1970. Singular value decomposition and least square solutions. Numerical Mathematics14, 403–420.
    [Google Scholar]
  4. GroomR.W. and BaileyR.C.1989. Decomposition of magnetotelluric impedance tensors in the presence of local three‐dimensional galvanic distortion. Journal of Geophysical Research94B, 1913–1926.
    [Google Scholar]
  5. GroomR.W. and BaileyR.C.1991. Analytic investigations of the effects of near surface three‐dimensional galvanic scatterers on MT tensor decompositions. Geophysics56, 496–518.
    [Google Scholar]
  6. JiracekG.R.1990. Near‐surface and topographic distortions in electromagnetic induction. Surveys in Geophysics11, 163–203.
    [Google Scholar]
  7. KaufmanA.A.1994. Geophysical Field Theory and Method, Part C: Electromagnetic Fields II. Academic Press, Inc..
    [Google Scholar]
  8. KaufmanA.A. and KellerG.V.1981. The Magnetotelluric Method. Elsevier Science Publishing Co.
    [Google Scholar]
  9. PorstendorferG.1975. Principles of magnetotelluric prospecting. Geoexploration Monographs, Geopublication Associates, Gebrüder Borntraeger.
    [Google Scholar]
  10. SingerB. Sh.1992. Correction for distortions of magnetotelluric fields: limits of validity of the static approach. Surveys in Geophysics13, 309–340.
    [Google Scholar]
  11. SternbergB.K., WashburneJ.C. and PellerinL.1988. Correction for the static shift in magnetotellurics using transient electromagnetic soundings. Geophysics53, 1459–1468.
    [Google Scholar]
  • Article Type: Research Article
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