The geomagnetic coast effect

Parkinson, W. D.; Jones, F. W.

doi:10.1029/rg017i008p01999

Cited by 121 publications

(87 citation statements)

References 133 publications

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“…When the Parkinson vectors are employed in surveying the momentary existence of earthquake-related high conductivity materials, influences of the coast effect and inhomogeneous conductivity of subsurface structure have to be considered. The coast effect (Parkinson and Jones, 1979;DeLaurier et al, 1983;Parkinson, 1983) is caused by an induction field resulting from differing conductivity properties of sea water, the oceanic and continental lithosphere and has been observed in countries such as Japan (Ogawa et al, 1986), Italy (Armadillo et al, 2001) and Australia (Hitchman et al, 2000). The coast effect causes that the induction arrows point toward the high conductivity sea water and remain simultaneously orthogonal to the nearby coastline.…”

Section: Methodsmentioning

confidence: 99%

“…The magnitude of an induction arrow is related to both the proximity of the conductor and its conductivity contrast with the background structure (Hitchman et al, 2000). Thus, the magnetic transfer function is usually applied to survey sites where the conductivity is higher than in the nearby areas (Parkinson, 1962;Parkinson and Jones, 1979) and it is widely utilised to study time-varying conductivity due to earthquakes (Zeng et al, 1995) and magnetic coast effects (Ogawa et al, 1986;Armadillo et al, 2001;Hitchman et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of seismo-electric anomalies using magnetic data in Taiwan

Chen

Hsu

Wen

et al. 2013

Nat. Hazards Earth Syst. Sci.

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The Parkinson vectors derived from 3-component geomagnetic data via the magnetic transfer function are discussed with respect to epicentre locations and hypocentre depths of 16 earthquakes (M ≥ 5.5) in Taiwan during a period of 2002–2005. To find out whether electric conductivity changes would happen particularly in the seismoactive depth ranges, i.e. in the vicinity of the earthquake foci, the frequency dependent penetration depth of the electromagnetic waves (skin effect) is taken into account. The background distributions involving the general conductivity structure and the coast effect at 20 particular depths are constructed using the Parkinson vectors during the entire study period. The background distributions are subtracted from the time-varying monitor distributions, which are computed using the Parkinson vectors within the 15-day moving window, to remove responses of the coast effect and underlying conductivity structure. Anomalous depth sections are identified by deviating distributions and agree with the hypocentre depths of 15 thrust and/or strike-slip earthquakes with only one exception of a normal fault event

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evaluation of seismo-electric anomalies using magnetic data in Taiwan

Chen

Hsu

Wen

et al. 2013

Nat. Hazards Earth Syst. Sci.

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“…Across coastlines, the lateral contrast in conductivity between sea-water and continental crust gives rise to a distinct geomagnetic coast effect (Parkinson and Jones, 1979). Although the coast effect is dominated by the conductivity contrast at the surface, it is also dependent on the conductivity of the underlying crust and mantle.…”

Section: Introductionmentioning

confidence: 99%

Two-Dimensional Electrical Conductivity Structure across the Southern Coastline of Australia.

White

Heinson

1994

J. geomagn. geoelec

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Geomagnetic field measurements have been made at three new seafloor locations off the coast of southern Australia, to extend a magnetometer array deployed by White and Polatayko (1978). Geomagnetic depth sounding (GDS) and vertical gradient sounding (VGS) estimates provide a measure of both the TE and TM mode response of the continent-ocean boundary, which is relatively two-dimensional (2D) over hundreds of kilometres. The seafloor data from the continental shelf, mid-continental slope and at the edge of the abyssal plain show a strong geomagnetic coast effect which can largely be accounted for by the sea-water and a thick wedge of sediments in a rifted marginal basin on the continental shelf. A 2D inversion of the GDS and VGS estimates to determine the sub-seafloor conductivity structure suggests that (a) the oceanic crust and continental crust have conductivities of 0.05 and 0.005 S-m ' respectively to a depth of 10 km, (b) the upper mantle above 140 km has conductivity 0.01-0.003 S-m', (c) the upper mantle between 140 and 390 km has conductivity less than 0.003 S-m ', and (d) the lower mantle below 390 km has conductivity less than 0.3 S•m'. No distinct boundary between oceanic and continental lithosphere conductivity can be discerned. The conductivity structure beneath the coastline of southern Australia is somewhat less conductive than the preferred model ofKellett et al. (1991) for southeastern Australia.

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“…As the ocean effect usually extends some 200 km inland (PARKINSON and JONES, 1979) no site in New Zealand should be free from it, but at a station midway between two parallel coastlines the two opposing effects should cancel. The ocean effect was recognised in New Zealand as early as 1927 by BAIRD (1927) and SKEY (1928) from observations at the Amberley magnetic observatory near Christchurch on the east coast of South Island and more recently by KELLETT et al (1988) at Eyrewell, which replaced Amberley in 1978 and which is situated 43 km to the southwest of Amberley.…”

Section: Introductionmentioning

confidence: 99%

A New Zealand Wide Magnetometer Array Study.

Chamalaun

McKnight

1993

J. geomagn. geoelec

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An array of three-component magnetometers was operated across the whole of New Zealand from November 1991 till April 1992, and the transfer functions have been computed for 34 sites. The results show that the ocean effect dominates the induction arrows. An attempt to remove the ocean effect by means of a thin sheet numerical model has not produced unambiguous evidence for induction effects associated with the underlying subduction zones. If such effects are present then they are small compared with the ocean effect and a much finer numerical grid with very detailed bathymetry is required to detect them.

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The geomagnetic coast effect

Cited by 121 publications

References 133 publications

Evaluation of seismo-electric anomalies using magnetic data in Taiwan

Evaluation of seismo-electric anomalies using magnetic data in Taiwan

Two-Dimensional Electrical Conductivity Structure across the Southern Coastline of Australia.

A New Zealand Wide Magnetometer Array Study.

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