The ocean-coast effect re-examined

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

doi:10.1111/j.1365-246x.1981.tb02735.x

Cited by 18 publications

(7 citation statements)

References 4 publications

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“…for a sheet current it is greater than for a line current (with R fixed). R varies greatly from event to event due to the variations in the primary current system, as Kisabeth & Rostoker (1977, An idealized thin-sheet model to estimate the ocean effect is given by Fischer, Schnegg & Usadel (1978) (for correction of an error in this paper, see Raval, Weaver & Dawson 1981). They assume a plane-wave primary field, but an extension to a laterally inhomogeneous field is straightforward (Viljanen 1992, Section 3.3.2).…”

Section: Theoretical Interpretationmentioning

confidence: 98%

On induction effects at EISCAT and IMAGE magnetometer stations

Viljanen¹,

Kauristie²,

Pajunpää³

1995

Geophysical Journal International

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S U M M A R YWhen ground-based magnetometer data are used for ionospheric/magnetospheric studies, it is important to know the external (ionospheric/magnetospheric) and internal (telluric) contributions to the observed total variation. To study them, we calculate geomagnetic induction vectors, and apply the Siebert-Kertz separation method using data from the EISCAT and IMAGE magnetometer stations in Fennoscandia. Induction vectors in the period range 20-2560 s show the expected, and dominating, ocean effect near the Arctic Ocean. At Masi, a small-scale inland anomaly is detected in addition to the ocean effect. At Hankasalmi a man-made anomaly due to the nearby STARE radar is present. The source effect on induction vectors at high latitudes is briefly investigated. By separating the magnetic variations of several bay events at IMAGE stations into external and internal parts, we study the importance of the large-scale induction in the recordings. Depending very much on the particular event, the internal horizontal part is 10-30 per cent of the total field in the auroral electrojet region, and its relative contribution increases in more distant regions. The internal contribution of the vertical field at inland stations is 10-40 per cent (having an opposite sign to the total field), or 10-30 per cent (having the same sign as the total field), depending on the location with respect to the ionospheric currents and to the ocean. Results are also discussed using a thin-sheet model.

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Section: Theoretical Interpretationmentioning

confidence: 98%

On induction effects at EISCAT and IMAGE magnetometer stations

Viljanen¹,

Kauristie²,

Pajunpää³

1995

Geophysical Journal International

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“…Other E-polarization problems have also been solved. Fischer, Schnegg & Usadel (1978), and later Raval, Weaver & Dawson (1981), considered the E-polarization mode solution for Bailey's model. This was later extended to the case of E-polarization induction in two adjacent thin half-sheets of differing finite integrated conductivities, on a uniformly conducting half-space, by Dawson ( 1983).…”

Section: Introductionmentioning

confidence: 99%

B-polarization induction in two thin half-sheets coupled to the mantle by a conducting crust-I. Solution by the Wiener-Hopf technique, with limiting forms

Dawson

1996

Geophysical Journal International

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S U M M A R YThe Wiener-Hopf technique is used to obtain an exact analytical solution to the problem of B-polarization induction in two adjacent thin half-sheets lying on a conducting layer, which is terminated at finite depth by a perfect conductor. The model may be viewed as an idealized local approximation to the Earth, with the half-sheets representing conducting layers (including the oceans) at the surface of the Earth, the conducting layer representing the crust, and the perfect conductor approximating the mantle. The solution may be used to study the behaviour of currents and electromagnetic fields induced in the Earth by ionospheric sheet-current sources flowing perpendicular to the thin-sheet junction. The solution allows for analytical investigation of the behavior of the field components near the thin-sheet junction. It also leads to some additional insight into the adjustment distance question.The model is a generalization of ones considered in three earlier publications by various authors. It is demonstrated that the field solutions for the present model contain those for the three earlier models as limiting cases, when one or more of the thin-sheet integrated conductivities become zero or infinite, or when the mantle depth becomes infinite. Also under appropriate limits, the model may also be viewed as a generalized thin sheet lying on a perfect conductor.

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“…In the absence of a fault and of a conducting talus or scree, they would have to be looked at as being located on very resistive ground but immediately adjacent to a highly conducting formation. This is somewhat reminiscent of an ocean coast situation, and one would therefore expect a rather anisotropic impedance with a small apparent resistivity in the E-POL configuration and a large one for H-POL (cf, FISCHER et al, 1978;FISCHER, 1979;and RAVAL et al, 1981). The absence of any anisotropy is strong evidence by itself that there must be a fault as sketched in Fig.…”

Section: Amt Sounding Resultsmentioning

confidence: 92%

Audio-magnetotelluric study of a structure with a reverse fault.

Schnegg

Quang

Fischer

et al. 1983

J. geomagn. geoelec

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A two-dimensional (2-D) structural transition from a flat valley floor to a mountain slope, with a presumed reverse fault at its base, was investigated by the audio-magnetotelluric sounding method. By calling on previously available geological information, it was possible to reformulate the problem so that only two basic questions remained to be answered: (1) does the structure effectively involve a fault, and (2) if so what is the dip angle of this fault? Since the soundings away from the mountain furnished the 1-D valley structure, it was possible to construct a 2-D model in which the only specified parameter was the unknown dip angle. Even the absence of a fault could be simulated in the model by giving this parameter a definite value. The model responses were computed numerically by the technique of finite differences and compared with the measured response curves, yielding quite clear answers in favor of a reverse fault dipping at an information concerning details of the valley structure.

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The ocean-coast effect re-examined

Cited by 18 publications

References 4 publications

On induction effects at EISCAT and IMAGE magnetometer stations

On induction effects at EISCAT and IMAGE magnetometer stations

B-polarization induction in two thin half-sheets coupled to the mantle by a conducting crust-I. Solution by the Wiener-Hopf technique, with limiting forms

Audio-magnetotelluric study of a structure with a reverse fault.

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