An analogue model study of electromagnetic induction for cape and bay coastlines

Chan, G.H.; Dosso, H. W.; Law, L. K.

doi:10.1016/0031-9201(81)90150-3

Cited by 15 publications

(8 citation statements)

References 9 publications

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“…The response of the continental coastline for all traverses is generally small as expected for this large bay shaped coastline for the present source field polarization (E-polarization). This effect has been discussed by CHAN et al, (1981b) in studying the response of bay coastlines, and also agrees with the results of Dosso et al (1980b) for the Gulf of St. Lawrence region of eastern Canada. The response of the peninsula coastline for traverses T2, and T3 which just by-passes the tip of the peninsula, is expected to be large, since it shows the combined effect of that due to a cape coastline and that due to the narrow Hainan Strait.…”

Section: Discussion Of Resultssupporting

confidence: 87%

“…The response of the peninsula coastline for traverses T2, and T3 which just by-passes the tip of the peninsula, is expected to be large, since it shows the combined effect of that due to a cape coastline and that due to the narrow Hainan Strait. Current induced in the ocean and deflected by a protruding cape (or peninsula) results in current concentration at the tip of the cape and the expected associated magnetic field enhancement (CHAN et al, 1981b;Dosso et al, 1980b The response of Hainan Island is described by the fields for traverses T2-T5 in Fig. 2.…”

Section: Discussion Of Resultsmentioning

confidence: 99%

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Laboratory model magnetic fields for the Hainan Island region.

Nienaber

Dosso

1983

J. geomagn. geoelec

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The behaviour of the electromagnetic fields over the Hainan Island region of the South China Sea is studied using a scaled laboratory analogue model. The model source frequencies used simulate periods of 5 min. to 30 min. in the geophysical scale. To examine the electromagnetic field variations due to the irregular coastlines, the deep ocean, a narrow ocean channel, and an atoll (modelled as a seamount), field components for individual traverses over the model are presented.The coast effect for the bay coastline is visible only for short periods at which the depth of the bay is at least .1 skin depths. The response of the seamount, overlain by a 500m depth ocean, differs greatly from the response of an island. Electric current flow over the seamount, confined to this thin layer, produces a quadrature field directly opposite to that for an island. Buried features such as the seamount and depth profile of the deep ocean show the largest in-phase response at the lower frequency where the overlying ocean is much less than .1 skin depth thick.

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Section: Discussion Of Resultssupporting

confidence: 87%

Section: Discussion Of Resultsmentioning

confidence: 99%

Laboratory model magnetic fields for the Hainan Island region.

Nienaber

Dosso

1983

J. geomagn. geoelec

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“…This indicates that current channelling in the very narrow ocean channels is important for the H -Polarization as well. Traverse T6, shows an extremely large Ey enhancement over the bay shaped continental coastline, in agreement with the augmented enhancement at a bay observed by CHAN et al (1981).…”

Section: Traverses For the H-polarization Case For A Conducting Layersupporting

confidence: 83%

“…Traverse T6 provides an example of reduced coast effect for HZ. The maximum in the coastal HZ enhancement is shifted seaward from the coastline, as is expected for a traverse through the central region of a bay (CHAN et al, 1981).…”

Section: Discussion Of Resultsmentioning

confidence: 56%

An analogue model study of electromagnetic induction in the Queen Charlotte Islands region.

Chan

Dosso

Nienaber

1981

J. geomagn. geoelec

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In order to ease the interpretation of geomagnetic data for resource charting and tectonic studies of the Queen Charlotte Islands region, the behaviour of the electromagnetic variations over the region is studied using a laboratory analogue model. The results indicate that conductive channelling is important in Hecate Strait for both E and H source field polarizations. Current deflection is observed at Rose Point for E-Polarization and at the northern and southern tips of the Queen Charlotte Islands for H-Polarization. Model results for simulated variations of 4, 40, and 120min show a wide range of field values over the Queen Charlotte Islands, for example, HZ varies by a factor of 4 or more between coastal and inland locations for E-Polarization at short periods and by as much as a factor of 5 between certain coastal locations at long periods. The model results show that in decreasing the depth of the conducting layer in the mantle from 200 to 100km, the Hz, Hx, Ex, and EY anomalies are attenuated by 20%, and the Hy anomalies by roughly 8% over the deep ocean and by 12% over Hecate Strait for 4min period variations.

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“…Also, the existence of certain of the 'crustal' anomalies quoted in Table II is suspect due to the presence of irregular coastlines and nearby islands this is true of Alert, Mould Bay, Greenland, Morocco, Britanny, and the Palk Strait. For all measurements close to coastlines, the observations can be very dependent on the highly local character of the shape of the coastline, as was shown in the analogue modelling study of capes and bays by Chan et al (1981). Also, the presence of an island off the coast can lead to apparently anomalously large magnetic fields being observed (see, for example, Nienaber et al, 1976Nienaber et al, , 1977Ramaswamy et al, 1977).…”

Section: Fieldmentioning

confidence: 90%

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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An analogue model study of electromagnetic induction for cape and bay coastlines

Cited by 15 publications

References 9 publications

Laboratory model magnetic fields for the Hainan Island region.

Laboratory model magnetic fields for the Hainan Island region.

An analogue model study of electromagnetic induction in the Queen Charlotte Islands region.

The problem of current channelling: A critical review

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