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Magnetic distortion of the magnetotelluric tensor: a numerical study


Decomposition of the magnetotelluric (MT) tensor when the electric field alone is subject to local galvanic distortion has received much attention in recent years. Recently some authors have extended such procedures to include the effects of the associated magnetic field distortion as well. With the aid of a three-dimensional modelling program the validity of the assumptions made in these analyses have been examined by considering the response over a range of periods of a small conductive cube at the surface of the earth and near a two-dimensional fault. The study indicates that the inclusion of magnetic distortion is necessary and important at short periods when induction occurs in the anomaly itself, but that the elements defining the magnetic distortion matrix become complex at such periods so that the assumptions underlying the theory are no longer valid. At longer periods the magnetic distortion matrix does become real and frequency-independent and therefore determinate, but its effect on the response becomes insignificant compared with that due to electric distortion. At these longer periods the phases of the regional impedances and the ratios of the electric distortion parameters are correctly recovered whether magnetic distortion is present or not. Calculations were repeated for a resistive cube, and also for a highly resistive region beneath the surface layer, with no significant enhancement of magnetic distortion. It is concluded that, at least for such models, inclusion of magnetic distortion in decompositions of the MT tensor does not, in general, offer any improvement over the conventional decompositions in which only distortion of the electric field is taken into account.


  1. Bahr, K., Interpretation of the magnetotelluric impedance tensor: regional induction and local telluric distortion, J. Geophys., 62, 119–127, 1988.

    Google Scholar 

  2. Chave, A.D. and A. G. Jones, Electric and magnetic field galvanic distortion decomposition of BC87 data, J. Geomag. Geoelec., 49, 767–789, 1997.

    Article  Google Scholar 

  3. Chave, A. D. and J. T. Smith, On electric and magnetic galvanic distortion tensor decompositions, J. Geophys. Res., 99, 4669–4682, 1994.

    Article  Google Scholar 

  4. Groom, R. W. and K. Bahr, Corrections for near surface effects: decomposition of the magnetotelluric impedance tensor and scaling corrections for regional resistivities: a tutorial, Surv. Geophys., 13, 341–379, 1992.

    Article  Google Scholar 

  5. Groom, R. W. and R. C. Bailey, Decomposition of the magnetotelluric impedance tensor in the presence of local three-dimensional galvanic distortion, J. Geophys. Res., 94, 1913–1925, 1989.

    Article  Google Scholar 

  6. Smith, J. T., Estimating galvanic-distortion magnetic fields in magnetotellurics, Geophys. J. Int., 130, 65–72, 1997.

    Article  Google Scholar 

  7. Weaver, J. T., A. K. Agarwal, and X. H. Pu, Three-dimensional finite-difference modelling of the magnetic field in geo-electromagnetic induction, in Three Dimensional Electromagnetics, edited by M. J. Oristaglio and B. R. Spies, Geophysical Developments Series Vol. 7, pp. 426–443, Society of Exploration Geophysicists, Tulsa OK, 1999.

    Google Scholar 

  8. White, S. N., A. D. Chave, and J. H. Filloux, A look at galvanic distortion in the Tasman Sea and the Juan de Fuca plate, J. Geomag. Geoelectr., 49, 1373–1386, 1997.

    Article  Google Scholar 

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Correspondence to A. K. Agarwal.

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Agarwal, A.K., Weaver, J.T. Magnetic distortion of the magnetotelluric tensor: a numerical study. Earth Planet Sp 52, 347–353 (2000).

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  • Apparent Resistivity
  • Tensor Decomposition
  • Galvanic Current
  • Magnetic Distor
  • Distortion Matrix