Electric and Magnetic Field Galvanic Distortion Decomposition of BC87 Data.

Chave, Alan D.; Jones, Alan G.

doi:10.5636/jgg.49.767

Cited by 40 publications

(34 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…There are both magnetic and electric effects of the charges (see e.g. Chave & Smith 1994;Chave & Jones 1997;) but the magnetic effects drop off very quickly with increasing period for isolated anomalies.…”

Section: Sensitivity Analysismentioning

confidence: 99%

“…It should be noted that the magnetic effects caused by galvanic distortion charges do affect Z, H and T (e.g. Chave & Smith 1994;Chave & Jones 1997), however, these effects rapidly decrease with increasing period due to the square root dependence of their sensitivity on frequency, and can effectively be ignored over broad frequency bands. This rapid decrease is true for pure galvanic distortion but not in other situations as for example in the case of presence of current channelling caused by thin-long structures (e.g.…”

mentioning

confidence: 99%

See 1 more Smart Citation

The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study

Campanyà¹,

Ogaya²,

Jones³

et al. 2016

Geophys. J. Int.

Self Cite

View full text Add to dashboard Cite

: The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study. -Geophysical Journal International, 207, 3, pp. 1818-1836 S U M M A R YAs a consequence of measuring time variations of the electric and the magnetic field, which are related to current flow and charge distribution, magnetotelluric (MT) data in 2-D and 3-D environments are not only sensitive to the geoelectrical structures below the measuring points but also to any lateral anomalies surrounding the acquisition site. This behaviour complicates the characterization of the electrical resistivity distribution of the subsurface, particularly in complex areas. In this manuscript we assess the main advantages of complementing the standard MT impedance tensor (Z) data with interstation horizontal magnetic tensor (H) and geomagnetic transfer function (T) data in constraining the subsurface in a 3-D environment beneath a MT profile. Our analysis was performed using synthetic responses with added normally distributed and scattered random noise. The sensitivity of each type of data to different resistivity anomalies was evaluated, showing that the degree to which each site and each period is affected by the same anomaly depends on the type of data. A dimensionality analysis, using Z, H and T data, identified the presence of the 3-D anomalies close to the profile, suggesting a 3-D approach for recovering the electrical resistivity values of the subsurface. Finally, the capacity for recovering the geoelectrical structures of the subsurface was evaluated by performing joint inversion using different data combinations, quantifying the differences between the true synthetic model and the models from inversion process. Four main improvements were observed when performing joint inversion of Z, H and T data: (1) superior precision and accuracy at characterizing the electrical resistivity values of the anomalies below and outside the profile; (2) the potential to recover high electrical resistivity anomalies that are poorly recovered using Z data alone; (3) improvement in the characterization of the bottom and lateral boundaries of the anomalies with low electrical resistivity; and (4) superior imaging of the horizontal continuity of structures with low electrical resistivity. These advantages offer new opportunities for the MT method by making the results from a MT profile in a 3-D environment more convincing, supporting the possibility of high-resolution studies in 3-D areas without expending a large amount of economical and computational resources, and also offering better resolution of targets with high electrical resistivity.

show abstract

Section: Sensitivity Analysismentioning

confidence: 99%

mentioning

confidence: 99%

The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study

Campanyà¹,

Ogaya²,

Jones³

et al. 2016

Geophys. J. Int.

Self Cite

View full text Add to dashboard Cite

show abstract

“…3), it can be appreciated that a good correlation of the surface geology strike direction with a geoelectric average strike angles exists. The length of the arrow denotes how well the data are fit by the distortion model; long arrows indicate an excellent fit of the distortion model to the data and short arrows indicate a poor fit owing to either overly optimistic error estimates (see Chave and Jones 1997) or to 3-D inductive effects because of complex 3-D geometry of conductive structures. The decomposition analysis suggests a regional strike angle of 60°for the frequencies corresponding to EM-wave penetration in the upper 70 km.…”

Section: Dimensionality and Distortion Analysismentioning

confidence: 99%

Electromagnetic image of the Trans-Hudson orogen THO94 transect

García

Jones

2005

Can. J. Earth Sci.

View full text Add to dashboard Cite

Abstract:The North American Central Plains (NACP) anomaly in enhanced electric conductivity and its relationship with the Paleoproterozoic Trans-Hudson orogen (THO) has been studied under the auspices of Lithoprobe for over a decade. The NACP anomaly was the first geophysical evidence of the existence of the THO beneath the Phanerozoic sediments of the Central Plains. This anomaly, detected geomagnetically in the late 1960s, has been the subject of a number magnetotelluric studies from the early 1980s. The PanCanadian and Geological Survey of Canada experiments in the 1980s and the Lithoprobe experiments in the 1990s together comprise four east-west and one north-south regional-scale profiles in Saskatchewan perpendicular to the strike of the orogen. In this paper, data from the northernmost line, coincident with seismic line S2B, are analysed and interpreted, and are shown to be key in determining the northern extension of the NACP anomaly. Dimensionality analysis confirms the rotation of deep crustal structures eastward to Hudson Bay, as earlier proposed on the basis of broad-scale geomagnetic studies. On this profile, as with the profile at the edge of the Paleozoic sediments, the NACP anomaly is imaged as lying within the La Ronge domain, in contact with the Rottenstone domain, and structurally above the Guncoat thrust, a late compressional feature. The location of the anomaly together with the surface geology suggests that the anomaly is caused either by sulphide mineralization concentrated in the hinges of folds, by graphite, or by a combination of both. Our interpretation of the data is consistent with that from other profiles, and suggests that the NACP anomaly was formed as a consequence of subduction and collisional processes involving northward subduction of the internides of the THO beneath the Hearne craton. On the southern part of this profile, a resistive structure is identified as the Sask craton, suggesting that Proterozoic rocks are above Archean rocks in the THO. 493Résumé : L'anomalie des plaines du centre de l'Amérique du Nord en conductivité électrique amplifiée et sa relation avec l'orogène trans-hudsonien (Paléoprotérozoïque) ont été étudiées dans le cadre du projet Lithoprobe depuis plus d'une décennie. Cette anomalie a été la première évidence géophysique de l'existence de l'orogène trans-hudsonien sous les sédiments phanérozoïques des plaines centrales. Cette anomalie, détectée par des techniques géomagnétiques à la fin des années 1960, a été le sujet de nombreuses études magnétotelluriques (MT) à partir du début des années 1980. Les expériences de PanCanadian et de la Commission géologique du Canada dans les années 1980, ainsi que celles du projet Lithoprobe dans les années 1990, comprennent ensemble, à l'échelle régionale, en Saskatchewan, quatre profils est-ouest et un profil nord-sud qui sont perpendiculaires à la direction de l'orogène. Dans cet article, les données de la ligne la plus au nord, coïncidant avec la ligne sismique S2B, sont analysées et interprétées; elles s'avèrent ...

show abstract

“…The Phoenix estimates are too small at periods shorter than about 5 s, i.e., when the number of available estimates is large, and are too large at longer periods. Chave and Jones (1997) then attempted combined galvanic and magnetic distortion removal, and determined that the distortion model is statistically inadequate at some frequencies for quite a few sites.…”

Section: Bc87mentioning

confidence: 99%

“…Thin sheet modelling showed that the sites are greatly affected by the presence of the resistive Nelson batholith. Chave and Jones (1997) reprocess the 24 Hz sampling data from the original time series, and determine jackknife errors on the estimates. They show that, in the main, the estimates derived from Phoenix's processing and those from the robust processing compare quite well in the mid-band (5-500 s).…”

Section: Bc87mentioning

confidence: 99%