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On the influence of DC railway noise on variation data from Belsk and Lviv geomagnetic observatories

Neska A., Reda J., Neska M., Sumaruk Y.

Acta Geophysica

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2013

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Vol. 61, no. 2

385--403

EN

Geomagnetic variation data from the observatories in Belsk (BEL, Poland) and Lviv (LVV, Ukraine) significantly suffer from disturbances caused by direct current (DC) electric railways. The aim of this study is to quantify the impact of these disturbances on quantities derived from such data, as the K index of magnetic activity and the induction arrow used in the geomagnetic deep sounding method to indicate lateral contrasts of elec- tric conductivity in the solid earth. Therefore, undisturbed data have been reconstructed by means of a frequency-domain transfer function that relates the horizontal magnetic field components of the observatory to the ones synchronously recorded at a noise-free reference station. The comparison of the K index derived from original and reconstructed data shows an increase of quiet time segments by 29 per cent for LVV and by 14 per cent for BEL due to our noise removal procedure. Furthermore, the distribution of the corrected K indices agrees well with the one from the Niemegk observatory in Germany

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Effect of thin near-surface layer on the geomagnetic induction arrows: an example from the East European Platform

Jankowski J., Ernst T., Jóźwiak W.

Acta Geophysica Polonica

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2004

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Vol. 52, nr 3

349-361

EN

Nineteen deep geomagnetic soundings were made in NE Poland which belongs to the East European Platform. The calculated transfer functions show that the induction vectors are quite large, achieving 0.8. The maximum length of the vectors is at the period of about 300 s. Comparing the directions of the induction vectors with the map of the thickness of sedimentary cover we found a striking correlation with the crystalline basement depth isolines. An auxiliary 2D modelling and a thin-sheet model support the statement that substantial part of the vectors is due to induction in the sedimentary cover.

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Modeling of conductivity structures generating anomalous induction at the eastern margin of the Bohemian Massif and the West Carpathians

Cerv V., Kovacikova S., Pek J., Pecova J., Praus O.

Acta Geophysica Polonica

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2002

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Vol. 50, nr 4

527-545

EN

Coordinated field campaigns were organized in close co-operation with the Polish and the Slovak colleagues to obtain geomagnetic variation data at 150 temporary field sites situated along profiles traversing the West Carpathians and the eastern part of the Bohemian Massif. Geomagnetic transfer functions and induction vectors (arrows) were calculated from the variation data. Two zones of the anomalous induction were suggested across the region. The West Carpathian anomaly (WCA), manifested by full reversals of strike-perpendicular induction arrows, is evidently a quasi-linear inductive feature with 2-D internal structure. The anomaly at the eastern margin of the Bohemian Massif (BMA) is defined by fast changes of induction arrow azimuths, but contrary to 2-D setting, by large strike-parallel induction arrows suggesting 3-D effects. Generating anomalous vertical magnetic field maps for the hypothetical primary field of different orientations, we found the NNE/SSW direction of hypothetical primary field, at which the strongest anomalous response appeared. To understand 3-D conductivity effects in the area of BMA at the eastern margin of the Bohemian Massif, possible distortions were analyzed. At long periods in quasi-static approximation, a thin sheet can replace anomaly source with anomalous conductivity and the equivalent current systems in thin sheet are calculated across the whole region. Equivalent current systems were obtained both for the thin sheet in free space and for the thin sheet buried in a medium with finite resistivity. The depth of the thin sheet corresponding to the top level of the anomaly source was estimated at 15-18 km and at 10-12 km for the WCA and BMA zones, respectively. Using minimum gradient support and maximum smoothness stabilizers for the Tikhonov functional in the inversion procedure, we computed a model of conductance distribution within the unimodal thin sheet located at a depth of 10 km and surrounded by a uniform medium.