Three-dimensional induction in a non-uniform thin sheet at the surface of a uniformly conducting earth

Dawson, Trevor W.; Weaver, J. T.

doi:10.1111/j.1365-246x.1979.tb02566.x

Cited by 66 publications

(54 citation statements)

References 17 publications

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“…A more general approach to 3D induction in a non-uniform thin sheet is afforded by Dawson and Weaver's (1979) treatment, in which the model may have either an Epolarisation or B-polarisation configuration at 'infinity'. The method has so far been applied to model the Vancouver Island region (Dawson and Weaver, 1979), northern Scotland (Weaver, 1982) and northern Scandinavia (Jones and Weaver, 1981).…”

Section: Za(co ) = At(o)) Ha(co ) ~-L~'(co) Oa(co ) 3ff ~mentioning

confidence: 99%

The problem of current channelling: A critical review

Jones

1983

Geophysical Surveys

147

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Abstract. The notion that currents induced 'elsewhere', by external source fields, could wend their way in a frequency-independent ohmic-like manner through a region of interest has been the cause of many recent disputes within the geomagnetic induction community. In particular, two-dimensional (2D) models of the Rhinegraben, and of the region known as the 'Eskdalemuir anomaly' in southern Scotland, have been dismissed as erroneous by those who believe that the observations are more correctly interpreted as due to the effects of 'channelled' currents rather than 'induced' currents. In this review, attention is paid primarily to consider under what circumstances any perturbation of current flow, which may manifest itself as a 'DC-like' channelled current, could cause a 'problem' for those wishing to interpret their observations. Various concepts are introduced, particularly the ratio of 3D/2D current channelling numbers for the induction problem, which is shown to be the ratio of the length of the 3D body to the skin depth in the host medium. It is stressed that the worker must analyse his data by adequate statistical techniques, and that the simplest physical models possible, that describes the observations, must be sought. Finally, suggestions are made for further work to be undertaken.

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Section: Za(co ) = At(o)) Ha(co ) ~-L~'(co) Oa(co ) 3ff ~mentioning

confidence: 99%

The problem of current channelling: A critical review

Jones

1983

Geophysical Surveys

147

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“…It was further pointed out that charges collected at conductivity discontinuities are bound to effect the local electrical field (Price, 1973). Two formulations approximating 3D structures in thin-sheet ap- proximation for regional studies have been developed independently by Vasseur and Weidelt (1977) and by Dawson and Weaver (1979). Both this algorithms have been applied to a variety of synthetic problems.…”

Section: Thin-sheet Modelling For the Island Effectmentioning

confidence: 99%

Results from a magnetic survey and geomagnetic depth sounding in the post-eruption phase of the Barren Island volcano

et al. 2014

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The Geological Survey of India conducted a magnetic survey and geological studies in 1993 around Barren Island in the Andaman Sea on board the RV Samudra Manthan. Five ocean bottom magnetometers were deployed by the Indian Institute of Geomagnetism as a part of this cruise. The Curie isotherm profiles prepared from the seasurface magnetic data indicate a high heat flow in the east of Barren Island. These profiles also indicate the presence of a north-south structural barrier which has prevented upflow of volcanic material to the west of Barren Island. Ocean-bottom magnetometer data were recorded simultaneously at five sites for about 15 days and these have been used to determine the electrical conductivity structure beneath Barren Island. Magnetic variations recorded at the seafloor stations indicate a concentration of electric currents near the island instead of the usual effect where currents are deflected away from the island. Transfer functions, showing the relationship between the horizontal components of the seafloor stations and land station, have been computed and the quantitative estimates of the transfer functions across Barren Island indicate a high conducting zone at a depth of about 17-27 km. This zone may have been produced by an upwelling of the mantle material through the magma chamber. The structure of this conductive zone at the north and south of Barren Island seems to concentrate the flow of the subsurface electrical currents within the island and the current flow takes a sharp southward turn beneath the island. This north-south conducting zone may have caused a rise in the depth of the Curie isotherm mapped by a shipborne magnetic survey of this region. Most probably, a partial melting of this conductive zone (magma chamber) may have given rise to the volcanic activity on Barren Island.

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“…The charges collected at conductivity discontinuities affect the local electric field (Price, 1973). Examples of the formulations approximating 3-dimensional structures by thin sheets are those by Vasseur and Weidelt (1977), and Dawson and Weaver (1979). Such algorithms have been applied to a variety of real and synthetic problems.…”

Section: Numerical Modellingmentioning

confidence: 99%