Geomagnetic Fluctuation Anomalies Across the Southeast Australian Coast

R. L. Kellet; A. White; I. J. Ferguson; F. E. M. Lilley

doi:10.1071/EG988294

ISSN: 0812-3985
E-ISSN: 1834-7533

Geomagnetic Fluctuation Anomalies Across the Southeast Australian Coast
Authors R. L. Kellet^a, A. White^b, I. J. Ferguson^c and F. E. M. Lilley^d
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^a Research School of Earth SciencesAustralian National University, GPO Box 4 Canberra, ACT, 2601 ^b School of Earth SciencesThe Flinders University of South Australia, Bedford Park, SA, 5042 ^c Research School of Earth SciencesAustralian National University, GPO Box 4 Canberra, ACT, 2601 ^d Research School of Earth SciencesAustralian National University, G.P.O. Box 4 Canberra, ACT, 2601
Publisher: Australian Society of Exploration Geophysicists
Source: Exploration Geophysics, Volume 19, Issue 1-2, Mar 1988, p. 294 - 297
DOI: https://doi.org/10.1071/EG988294
- Published online: 01 Mar 1988

Abstract

Magnetic surveys are used in both mineral and hydrocarbon exploration to map the characteristic patterns of magnetisation of crustal rocks. However there is a part of the magnetic field of the earth which fluctuates with time and changes over seconds, minutes and hours. This fluctuating part of the magnetic field is due to the flow of electric currents both internal and external to the earth.

The fluctuating part is anomalously strong at coastlines, a phenomenon known as the ‘Geomagnetic Coast Effect’ which extends for distances of order 100 km either side of the coastline. A significant portion of the coast effect can be explained by large scale induction of electric current in the seawater. The electric conductivity structure of the continental margin will also influence the flow of electric current.

The south-east Australian coast is an ideal location for investigating this phenomenon due to its simple two-dimensional character and narrow continental shelf. Measurements of the fluctuating magnetic field were made using stationary magnetometers on land and seafloor during the Tasman project of Seafloor Magnetotelluric Exploration and the more recent Continental Slope Experiment. Within the accuracy of the station spacing, the coast effect has a maximum amplitude halfway across the continental slope.

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References

Bennett, D. J. and Lilley, F. E. M. (1974)—‘Electrical conductivity structure in the south-east Australian Region’, Geophys. J. R. Astr. Soc. 37, 191–206.
Chamalaun, F. H. and Walker, R. (1982)—‘A microprocessor based digital fluxgate magnetometer for geomagnetic deep sounding studies’, J. Geomag. Geoelectr. 34, 491–507.
Everett, J. E. and Hyndman, R. D. (1967)—‘Geomagnetic variations and electrical conductivity structure in south-western Australia’, Phys. Earth Planet. Int. 34, 46–56.
Ferguson, I. J. (1988)—‘The Tasman Project of Seafloor magnetotelluric Exploration’, Ph.D. Thesis, Australian National University, Canberra.
Ferguson, I. J., Filloux, J. H., Lilley, F. E. M., Bindoff, N. L. and Mulhearn P. J. (1985)—‘A seafloor magnetotelluric sounding in the Tasman Sea’, Geophys. Res. Lett. 12, No. 9, 545–548.
Filloux, J. H. (1973)—‘Techniques and Instrumentation for study of natural electromagnetic induction at sea,’ Phys. Earth Planet. Int. 7, 323–338
Filloux, J. H., Lilley, F. E. M., Ferguson, I. J., Bindoff, N. L. and Mulhearn P. J. (1985)—‘The Tasman Project of Seafloor Magnetotelluric Exploration’, Exploration Geophysics16, 221–224.
Lilley, F. E. M., Filloux, J. H., Ferguson, I. J., Bindoff, N. L., and Mulhearn P. J. (1988)—‘The Tasman Project of Seafloor Magnetotelluric Exploration: experiment and observations’, Phys. Earth Planet. Int., in press.
Parkinson, W. D. (1959)—‘Direction of rapid geomagnetic fluctuations’, Geophys. J. R. Astr. Soc. 2, 1–14.
Parkinson, W. D. and Jones, F. W. (1979)—‘The Geomagnetic coast effect’, Rev. Geophys. Space Phys. 17, 1999–2015.
Schmucker, U. (1964)—‘Anomalies of geomagnetic variations in the south-western United States’, J. Geomag. Geoelectr. 15, 193–221.

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Article Type: Research Article

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Geomagnetic Fluctuation Anomalies Across the Southeast Australian Coast

Abstract

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