Geological noise in magnetotelluric data: a classification of distortion types

Bahr, Karsten

doi:10.1016/0031-9201(91)90101-m

Cited by 326 publications

(280 citation statements)

References 11 publications

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“…For MT data, Zhang's strike and distortion model (Zhang et al 1987), Bahr's phase-sensitive skew (Bahr 1991) and the phase tensor (Caldwell et al 2004) were used for dimensionality and strike analyses.…”

Section: Mt Data Acquisition P Ro C E S S I N G a N D A N A Ly S I Smentioning

confidence: 99%

A magnetotelluric investigation of the Scandinavian Caledonides in western Jämtland, Sweden, using the COSC borehole logs as prior information

Yan¹,

Juanatey²,

Kalscheuer³

et al. 2016

Geophys. J. Int.

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Section: Mt Data Acquisition P Ro C E S S I N G a N D A N A Ly S I Smentioning

confidence: 99%

A magnetotelluric investigation of the Scandinavian Caledonides in western Jämtland, Sweden, using the COSC borehole logs as prior information

Yan¹,

Juanatey²,

Kalscheuer³

et al. 2016

Geophys. J. Int.

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“…A well-defined, midcrustal reflective boundary is imaged at 12_+2 km depth, below which the P-wave velocity increases to 6.44-6.45 km s -•. values (1-10 4 f2 m), but all sites indicate a general decrease in resistivity above 100 s. Although the apparent resistivity curves have been partially corrected for static shift effects via joint analysis of (audiomagnetotelluric) AMT and TEM data, decomposition [Bahr, 1988[Bahr, , 1991Groom and Bailey, 1989] indicates that some galvanic effects arise at periods corresponding to penetration depths deeper than the deepest penetrating TEM data. A number of sites, including OLO, IRK and NGU, which may lie close to boundaries, display marked phase splitting persisting to the longest periods.…”

mentioning

confidence: 99%

“…The expectation that the N-S geological strike of the rift in the region would entirely control the geoelectric strike is not substantiated by the data. Table 1 summarizes data above 10 s from 11 sites with period ranges (some of which, e.g., LUK, however, exhibit high phase-sensitive skews [Bahr, 1988]) for which a stable Bahr "strike" [Bahr, 1988[Bahr, , 1991 is apparent. Data quality in this period range can be seen from Figure 2.…”

mentioning

confidence: 99%

A three‐dimensional electromagnetic model of the southern Kenya Rift: Departure from two dimensionality as a possible consequence of a rotating stress field

Simpson¹

2000

J. Geophys. Res.

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Abstract. A generic, three-dimensional (3-D) model has been developed which explains the threedimensionality exhibited by magnetovariational (MV) and magnetotelluric (MT) data from southern Kenya. In this model, observed variations in electromagnetic strike with period and location, impedance phase splitting, and peaks in tipper magnitude are all understood in terms of two regionally two-dimensional (2-D) structures striking NW-SE and N-S, respectively. The observed period and location dependence of the electromagnetic strike may arise as an indirect consequence of a rotating stress field, with regional-scale structures formed at different stages of the stress-strain history of Kenya being preserved as conductive lineaments. These conductive structures are not all confined to the upper crust. Thus, whereas stress data provide constraints on rifting at the upper crustal scale, the MT impedance tensor data provide constraints at lithospheric scales. The constraints and resolution provided by the MV and MT data have been rigorously investigated using 3-D forward modeling. Decoupling of the period and site dependence of electromagnetic strike aids resolution and constraint of conductors, rendering attempts to fix an average strike in space and frequency inexpedient. An anomalous apparent "strike" at the center of the Rift Valley reflects neither the N-S strike of the riff, nor the NW-SE striking shear fabric, but is shown to be a virtual strike arising as a result of coupling between the respective strike directions. The NW-SE trending conductivity anomaly straddles the rift and both its flanks, extends to at least middle to lower crustal depths, and appears substantially more electrically anomalous than the rift itself. A hypothesis that melt exists in the mantle directly below the rift at latitude 1.8øS is not supported by the MT data.

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“…Localized (near-surface) 3D effects influence the response observed at site 4. The dimensional characteristics were also confirmed using the classification analysis scheme of Bahr (1991).…”

Section: Magnetotelluric Data Characteristicsmentioning

confidence: 81%

Deep resistivity imaging across the Northern and Central belts of the Southern Uplands

Beamish

1995

Geol. Mag.

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Magnetotelluric data from 16 soundings have provided a northwest-southeast traverse across the Northern and Central belts of the Southern Uplands. The 34 km profile extends from the Ordovician Portpatrick Formation (northwest of the Thornhill Basin) across the Silurian Gala Group onto the Permian Lochmaben Basin in the southeast. The survey traverses, and has particular relevance to, the Ordovician/ Silurian boundary (Orlock Bridge Fault), the associated Moniaive Shear Zone, and the Moffat Valley Lineament. The data obtained have been successfully modelled (inverted) to provide a crustal-scale resistivity cross-section. The two Upper Palaeozoic basins are resolved as relatively conducting features. Basin depths are about 200 m (Thornhill) and 1100 m (Lochmaben). Elsewhere, through the upper crustal interval, resistivities over 500 ohm m are associated with the Lower Palaeozoic greywackes. The Silurian formations appear more resistive (and slightly thicker) than their Ordovician counterparts. Depth to basement (base Lower Palaeozoic) is not a wellresolved characteristic but resistivity gradients observed below 5 km suggest a depth of this order. Concealed beneath the Thornhill Basin lie two narrow, vertical, conductive zones. The more substantial feature lies towards the northwest margin of the basin, and is probably associated with the Orlock Bridge Fault. The second zone lies towards the southeast margin of the basin. The conductivity minima, in both cases, are located in the depth range 2 to 3 km; they are separate and distinct from the overlying basin sediments. If the two anomalies, some 5 to 6 km apart, can be considered an expression of the Moniaive Shear Zone, then the major conductive constituents are concentrated at the margins. Two dipping, resistive features in the upper kilometre are imaged in the vicinity of the Moffat Valley Lineament.

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Geological noise in magnetotelluric data: a classification of distortion types

Cited by 326 publications

References 11 publications

A magnetotelluric investigation of the Scandinavian Caledonides in western Jämtland, Sweden, using the COSC borehole logs as prior information

A magnetotelluric investigation of the Scandinavian Caledonides in western Jämtland, Sweden, using the COSC borehole logs as prior information

A three‐dimensional electromagnetic model of the southern Kenya Rift: Departure from two dimensionality as a possible consequence of a rotating stress field

Deep resistivity imaging across the Northern and Central belts of the Southern Uplands

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