Geomagnetic variation anomalies in northern England: processing and presentation of data from a non-simultaneous array

Shen, P.Y.; Mansinha, L.

doi:10.1111/j.1365-246x.1983.tb01903.x

Cited by 28 publications

(17 citation statements)

References 43 publications

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“…In conventional inter-station transfer function analysis, a bivariate processing is performed, where all local geomagnetic components are directly related to horizontal magnetic components of a reference station, which serve as input channels in the processing [Schmucker, 1970;Beamish and Banks, 1983]. The multiple-station analysis developed by Egbert [1997] which we have used here, fully incorporates the simultaneity of the array data by calculating spectral density matrices SDM (matrix of averaged cross products for all components observed in the array), using a so-called multivariate errors-in-variables estimator.…”

Section: Array Data Analysismentioning

confidence: 99%

A magneto‐variation array study in the Central Andes of N Chile and SW Bolivia

Soyer¹,

Brasse²

2001

Geophysical Research Letters

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Section: Array Data Analysismentioning

confidence: 99%

A magneto‐variation array study in the Central Andes of N Chile and SW Bolivia

Soyer¹,

Brasse²

2001

Geophysical Research Letters

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“…5 ) single‐site vertical response functions are available. Additionally, difference field response functions (= local response functions A ℓ , B ℓ ) were computed for 35 sites on dense profiles covering an area of approximately 40 × 40 km across the Alston Block ( Beamish & Banks 1983). They were obtained by relating the differences of total and reference vertical fields at each site ( B z i ℓ = B z i − B z r ) to the horizontal field at a common reference site ( B z i ℓ = A ℓ B x r + B ℓ B y r ).…”

Section: 1 Vertical Magnetic Response Functionsmentioning

confidence: 99%

“…5 for T~750 s). Beamish & Banks (1983), Banks (1986) and Banks et al (1993Banks et al ( , 1996 pointed out that the anomaly associated with the Northumberland Trough is produced in part by current concentrations in the surface sediments but mainly in the mid-crustal conductor. From hypothetical event maps of a magnetometer array across the Alston Block (53 sites), Banks & Beamish (1984) concluded that, at periods around 1000 s, current channelling rather than induction is the ruling physical process in these extended structures.…”

Section: The Iapetus Data Setmentioning

confidence: 99%

Separation of local and regional information in distorted GDS response functions by hypothetical event analysis

Ritter

Banks

1998

Geophysical Journal International

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Electromagnetic investigations are usually intended to examine regional structures where induction takes place at a given period range. However, the regional information is often distorted by galvanic effects at local conductivity boundaries. Bahr (1985) and Groom & Bailey (1989) developed a physical distortion model for decomposing the MT impedance tensor, based upon local galvanic distortion of a regional 2‐D electromagnetic field. We have extended their method to predict the magnetic variation fields created at an array of sites. The magnetic response functions at periods around 1000 s may be distorted by large‐scale inhomogeneities in the upper or middle crust. In this period range, the data measured by a magnetometer array contain common information that can be extracted if the data set is treated as a unit, for example by using hypothetical event analysis. With this technique it is always possible to recover the regional strike direction from distorted data, even if a strong, spatially varying regional vertical field component is present in the data set. The determination of the regional impedance phases, on the other hand, is far more sensitive to deviations from the physical distortion model. The approach has been used to investigate the Iapetus data set. For the array, which covers an area of 200 km × 300 km in northern England/southern Scotland, the technique revealed a common regional strike azimuth of ca. N125° E in the period range 500–2000 s. This direction differs from the strike indicated by the induction arrows, which seem influenced mainly by local current concentrations along the east–west‐striking Northumberland Trough and a NE–SW‐striking mid‐crustal conductor. Both impedance phases are positive and differ by ca. 10°, which supports the assumptions of distortion fields in the data set and that the regional structure is 2‐D.

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“…The advantage and the limitations of the common reference site (interstation) transfer function vis-à-vis single-station transfer functions have been discussed by BEAMISH and BANKS (1983). However, in view of the difficulty of uniquely estimating the normal horizontal field, the MV fields recorded at station GOI are reckoned to be a likely measure of the normal field.…”

Section: Transfer Functionsmentioning

confidence: 99%

Magnetometer Array Study in North-Northeast Brazil: Conductivity Image Building and Functional Induction Modes

Arora

Rigoti

Vitorello

et al. 1998

Pure appl. geophys.

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Magnetovariational fields recorded by an array of magnetometers in the equatorial region of north-northeast Brazil are analyzed to infer the configuration of internal induced currents in and around the extensive intracratonic Parnaíba basin. Only nighttime magnetovariational fields were used because of the prevailing uniform source field conditions. For periods exceeding 40 min. the vertical fields at all inland sites are dominated by the effects of electric currents originating in the northeast, in the deep Atlantic Ocean. Below this period, although best developed in the 12 -15 min. period range, the anomalous signatures are principally controlled by two distinct continental current paths. The first is associated with a N60°E trending graben-like structure in the southeastern part of the basin (named the Parnaíba Basin Conductivity Anomaly-PBCA) and the second appears as a subsurface sedimentary channel, from the NW corner of the array to the central part of the basin. This is named the LINK anomaly, as it connects the northwestern Marajó basin with the Parnaíba basin. While the PBCA is shown to highlight the importance of basement tectonics in the geological evolution of the Parnaíba basin, the LINK anomaly provides strong geophysical evidence of the direction of the sea intrusion into the region of the basin and possibly indicates the connectivity of the Parnaíba basin to the adjoining Amazon basin through the Marajó basin. Frequency and polarization dependence suggest that the induction response of individual structures is not determined by the local conductivity alone but also by their interconnectivity as well as by their linkage to the continental shelf and deep oceanic region.

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Geomagnetic variation anomalies in northern England: processing and presentation of data from a non-simultaneous array

Cited by 28 publications

References 43 publications

A magneto‐variation array study in the Central Andes of N Chile and SW Bolivia

A magneto‐variation array study in the Central Andes of N Chile and SW Bolivia

Separation of local and regional information in distorted GDS response functions by hypothetical event analysis

Magnetometer Array Study in North-Northeast Brazil: Conductivity Image Building and Functional Induction Modes

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