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Stress Near the Surface of the Earth (1987)

Gough, D I ; Gough, W I

Palo Alto, Calif. : Annual Reviews

Annual Review of Earth and Planetary Sciences 15 (1987), S. 545-566

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ISSN: 0084-6597

Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff

Topics: Geosciences , Physics

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1146/annurev.ea.15.050187.002553

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Estimation of the magnetic fields of current channels in magnetovariational data (1989)

Wang, Xi-shuo ; Samson, J. C. ; Gough, D. I.

Oxford, UK : Blackwell Publishing Ltd

Geophysical journal international 96 (1989), S. 0

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ISSN: 1365-246X

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences

Notes: Electric currents induced in the Earth are concentrated, in many places, in rocks of anomalously high conductivity, which may have a locally elongated shape. If the currents in such a current channel close beyond the bounds of an area of observation, such as is provided by an array of magnetometers, we call them channelled currents. The presence of such currents can cause severe problems in the interpretation of magnetovariation fields. To identify current channels, which may carry channelled currents, we construct a data matrix with elements H(j, ω) where j indicates position and spatial component of the magnetovariation field and ω is frequency. If the fields are due to a single current channel, then the data matrix has the form of an outer product and H = uv†, where u is a real vector with components u(j), and v is a complex vector with components v(ω). This corresponds to the case where Re(HH†) has only one non-zero eigenvalue. Consequently the eigenvectors of the matrix Re(HH†) can be used to test for current channels. We also determine estimators for u and v based on a least-squares criterion. These estimators can be used to construct the three components of the magnetic fields of current channels over a two-dimensional surface. The efficacy of the method is illustrated by analysing data from a magnetometer array in western Canada. The analysis shows that the total and internal parts of the magnetovariation fields are dominated by currents in a single channel, whereas the external fields are not. As the current channel crosses the array it very probably carries channelled currents in the sense of this paper.