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Natural Fields Geophysics Technical Papers

Index

  1. Decomposition and Modelling of the BC87 Dataset
    1993. Alan G. Jones, Ross W. Groom and Ron D. Kurtz. Journal of Geomagnetism and Geoelectricity, vol. 45, p. 1127-1150.
  2. Strike-angle determination from the magnetotelluric impedance tensor in the presence of noise and local distortion: rotate at your peril!
    1993. Alan Jones and Ross Groom. Geophysical Journal International, vol. 115, p.524-534.
  3. A quantitative methodology to extract regional magnetotelluric impedances and determine the dimension of the conductivity structure
    1993. R.W.Groom, R.D.Kurtz, A.G.Jones and D.E.Boerner. Geophysical Journal International, vol. 115, p. 1095-1118.
  4. Corrections for Near Surface Effects: Decomposition of the Magnetotelluric Impedance Tensor and Scaling Corrections for Regional Resistivities
    1992. Ross W. Groom and Karsten Bahr. Surveys in Geophysics, vol. 13, p. 341-380.
  5. Analytic investigations of the effects of near-surface three-dimensional galvanic scatterers on MT tensor decompositions
    April 1991. R.W. Groom and R.C. Bailey. Geophysics, Vol.56, No.4, p.496-518.
  6. Quantitative Methodology for Determining the Dimensionality of Structure
    Oct 1989. Ross Groom, Ron Kurtz and David Boerner. 1989 SEG Conference, Dallas, Texas.
  7. Decomposition of Magnetotelluric Impedance Tensors in the Presence of Local Three-Dimensional Galvanic Distortion
    Feb 1989. Ross W. Groom and Richard C. Bailey. Journal of Geophysical Research, vol. 94, No. B2, p.1913-1925.
  8. Some Effects of Multiple Lateral Inhomogeneities in Magnetotellurics
    Jan 1989. R.W. Groom and R.C. Bailey. Geophysical Prospecting vol.37, p.697-712.

Full Listing

Title:
Decomposition and Modelling of the BC87 Dataset
By:
1993. Alan G. Jones, Ross W. Groom and Ron D. Kurtz. Journal of Geomagnetism and Geoelectricity, vol. 45, p. 1127-1150.
Description:
The BC87 data exhibit distortions due to three-dimensional structures at almost all scale sizes. These distortion effects must be identified and removed, as far as possible, prior to interpretation. A galvanic model of these distortions is shown to be valid for most of the frequency range of observation, but 3D induction is significant at certain sites for some bands. A first-order regression was fit to the decomposition recovered long period E-polarization apparent resistivities to correct for the remnant local site "static shifts".
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Title:
Strike-angle determination from the magnetotelluric impedance tensor in the presence of noise and local distortion: rotate at your peril!
By:
1993. Alan Jones and Ross Groom. Geophysical Journal International, vol. 115, p.524-534.
Description:
Determination of the strike of the dominant 2-D geoelectrical structure from magnetotelluric (MT) data is difficult in the presence of both noise and local distortion. This paper illustrates that often the strike angle is the least-stable parameter that can be resolved from the MT data themselves, and that the telluric distortion parameters are usually more robustly estimated. In particular, techniques which rely only on the analytical rotational properties of the MT impedance tensor can yield erroneous results in the presence of even small amounts of noise. The estimation procedure is stabilized once the telluric distortion parameters have been correctly determined and a constrained fit is sought. Also, it is emphasized that even when the true strike angle is known, statistically superior estimates of the regional impedances result when fitting a galvanic distortion model to the data rather than merely rotating the impedance tensor into the determined (or assumed) strike direction.
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Title:
A quantitative methodology to extract regional magnetotelluric impedances and determine the dimension of the conductivity structure
By:
1993. R.W.Groom, R.D.Kurtz, A.G.Jones and D.E.Boerner. Geophysical Journal International, vol. 115, p. 1095-1118.
Description:
A methodology to determine quantitatively the dimensionality of the dominant conducting structures and the resolution of the structural parameters in magnetotelluric data is presented.
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paper(PDF)

Title:
Corrections for Near Surface Effects: Decomposition of the Magnetotelluric Impedance Tensor and Scaling Corrections for Regional Resistivities
By:
1992. Ross W. Groom and Karsten Bahr. Surveys in Geophysics, vol. 13, p. 341-380.
Description:
This paper primarily examines the effects of small-scale or near-surface conductivity inhomogeneities on the magnetotelluric impedance tensor.
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paper(PDF)

Title:
Analytic investigations of the effects of near-surface three-dimensional galvanic scatterers on MT tensor decompositions
By:
April 1991. R.W. Groom and R.C. Bailey. Geophysics, Vol.56, No.4, p.496-518.
Description:
An outcropping hemispherical inhomogeneity embedded in a two-dimensional (2-D) earth is used to model the effects of three-dimensional (3-D) nearsurface electromagnetic (EM) "static" distortion. Analytical solutions are first derived for the galvanic electric and magnetic scattering operators of the heterogeneity. To represent the local distortion by 3-D structures of fields which were produced by a largescale 2-D structure, these 3-D scattering operators are applied to 2-D electric and magnetic fields derived by numerical modeling to synthesize an MT data set. Synthetic noise is also included in the data.
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Title:
Quantitative Methodology for Determining the Dimensionality of Structure
By:
Oct 1989. Ross Groom, Ron Kurtz and David Boerner. 1989 SEG Conference, Dallas, Texas.
Description:
A methodology is described to evaluate quantitatively the dimensionality of the conducting structure which governs a set of MT data. This methodology is based upon three general models or parametrizations of the MT tensor, each of which has a different physical interpretation.
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Title:
Decomposition of Magnetotelluric Impedance Tensors in the Presence of Local Three-Dimensional Galvanic Distortion
By:
Feb 1989. Ross W. Groom and Richard C. Bailey. Journal of Geophysical Research, vol. 94, No. B2, p.1913-1925.
Description:
There are many occasions on which the magnetotelluric impedance tensor is affected by local galvanic distortion (channelling) of electric currents arising from induction in a conductive structure which is approximately two-dimensional on a regional scale. Even though the inductive behavior is 2-D, the resulting impedance tensor can be shown to have three dimensional behavior. Conventional procendures for rotating the impedance tensor do not in general recover the principal axes of induction and thus do not recover the correct principal impedances but rather linear combinations of them. This paper presents a decomposition of the impedance tensor which separates the effects of 3D channeling from those of 2D induction.
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Title:
Some Effects of Multiple Lateral Inhomogeneities in Magnetotellurics
By:
Jan 1989. R.W. Groom and R.C. Bailey. Geophysical Prospecting vol.37, p.697-712.
Description:
The analytical solution, for the H-polarization magnetotelluric impedance, of a series of multiple, vertical, conducting slabs (dikes) embedded in a host medium is extended to an infinite array in order to model an anisotropic layer. The solution is used to study the effects of such strongly anisotropic media on the surface impedance. At low frequencies such vertically laminated structures behave as a bulk material. It is shown that the effective bulk parameters are those expected from d.c. theory. However, practical electrode separations may not be long enough or adequately positioned to correctly obtain these bulk parameters from the measured impedance. Thus, such structures can masquerade as quite different one-dimensional structures. A haphazard use of long electrode spacings will not necessarily produce correct results.
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