Numerical electromagnetic modeling including studies of characteristic dimensions: A review

Kaikkonen, P.

doi:10.1007/bf01904063

Cited by 15 publications

(5 citation statements)

References 81 publications

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“…Analytical solutions (Weaver, LeQuang & Fischer 1985, when available, are valuable for verifying the accuracy of more general numerical models. A fairly recent review by Kaikkonen ( 1986) considers some of the wide variety of numerical and analytical modelling methods that have been developed. The following paragraphs present a brief review of some numerical and analytical forward models that have been based on thinsheet theory.…”

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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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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“…Some examples include Hibb. and Jones (1978), Mareschal (1981Mareschal ( , 1986, Jones (1980Jones ( , 1981, Jones et al (1983), Kaikkonen (1986), Hermance (1984) , andOsipova et al (1989). Mareschal (1986) gave a particularly good review of the influence of nonuniform source fields on the MT transfer functions for a ID earth.…”

Section: :00mentioning

confidence: 99%

Robust processing of magnetotelluric data in the AMT dead band using the continuous wavelet transform

García

Jones

2008

GEOPHYSICS

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Magnetotelluric (MT) data acquired during September-October I 1994, in northern Canada, were strongly influenced by non-uniform source field contributions from the aurora1 electrojet, and especially by intense auroral episodes. The largest effect on the estimate of the magnetotellwic impedance tensor elements was during intervals of highest magnetic activit.y, which primarily correlated with high auroral activity and wa::; observoo during local night time. In comparison, during the day the effect on the normal magneto telluric impedance tensor response was usually, but not always, small. A robust controlled-leverage processing algorithm was applied to these data in an attempt to extract the stable lLniform field estima.tes of the impedance. The differences between nonrobust and robust processing of the entire data set is compared to that obtained after dividing the time series into daytime and nighttime segments. The nonrobust estima.te using all data is controlled by the nocturnal data, which are, in turn. dominated by non-uniform source effects. However, nonrobust processing of only the daytime data fails to recover a useful result. There is little difference between the robust response for the eutire Wld daytime data. provided that the fruction of auroral activity is not large, i.e., in excess of half of the available data series. In addition, examination of the time-dependence of the response functions shows that the strongest bias is observed during the initial quarter of an auroral event.

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“…Previous studies [ Price , 1949; Sasai , 1968; Vasseur and Weidelt , 1977; Dawson and Weaver , 1979; McKirdy et al , 1985] have shown that the inductive/conductive effects of the ocean can be well approximated by modeling EM induction in three‐dimensional (3‐D) nonuniform thin sheets of variable conductance placed on the Earth's surface. The periods of the geomagnetic temporal variation in concern should fulfill the so‐called “thin sheet conditions” [ Agarwal and Weaver , 1989; Kaikkonen , 1986; Park , 1985; Schmucker , 1970] in order to validate the approximation. Here, “conductance” is understood to be the product of electrical conductivity and thickness.…”

Section: Forward Problemmentioning

confidence: 99%

Mantle upwelling revealed by genetic algorithm inversion of the magnetovariational anomaly around Kyushu island, Japan

Toh

Honma

2008

J. Geophys. Res.

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[1] The spatial extent of an outstanding mantle upwelling in the west of Kyushu island, Japan, has been estimated by a genetic algorithm inversion. Here we show how the mantle upwelling manifests in modeling of observed anomalies of temporal geomagnetic variations, i.e., magnetovariational anomalies around southwest Japan. Observed ratios of the vertical to horizontal geomagnetic components at short periods are known as indicators of subsurface electrical contrasts. However, they are also sensitive to the presence of oceans and continents because of much more conductive seawater than land rocks. To circumvent the difficulty, we used three-dimensional nonuniform thin sheet approximation to subtract out the conductive as well as inductive effects of the ocean on the magnetovariational anomalies. The observed anomalies were then inverted by a genetic algorithm inversion for conductance (the product of electrical conductivity and thickness) with the known bathymetry as a priori information. The derived conductance model has particular sensitivity to the northeastern portion of spatial extent of the mantle upwelling probably centered at the East China Sea. The upwelling may result in horizontal flows of the uppermost mantle, which induce the horizontal stress field that can trigger hazardous shallow intraplate earthquakes of large magnitude, such as the earthquake off the west coast of Fukuoka Prefecture that occurred on 20 March 2005. The northeastern rim of the mantle upwelling thus revealed can also be related to an unidentified boundary between the Amurian plate and the Eurasia plate.Citation: Toh, H., and S. Honma (2008), Mantle upwelling revealed by genetic algorithm inversion of the magnetovariational anomaly around Kyushu island, Japan,

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Numerical electromagnetic modeling including studies of characteristic dimensions: A review

Cited by 15 publications

References 81 publications

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

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

Robust processing of magnetotelluric data in the AMT dead band using the continuous wavelet transform

Mantle upwelling revealed by genetic algorithm inversion of the magnetovariational anomaly around Kyushu island, Japan

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