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Results of Crust and Mantle Soundings in Central and Northern Europe in the 21st Century

Semenov V. Yu.

Acta Geophysica

2015

Vol. 63, no. 1

103--124

The first decade of 21st century is characterized by the appearance of new approaches to deep induction soundings. The theory of magnetovariation and magnetotelluric soundings was generalised or corrected. Spatial derivatives of response functions (induction arrows) were obtained for the ultra-long periods. New phenomena have been detected by this method: secular variations of the Earth’s apparent resistivity and the rapid changes of induction arrows over the last 50 years. The first one can be correlated with the number of earthquakes, and the second one – with geomagnetic jerks in Central Europe. The extensive studies of geoelectrical structure of the crust and mantle were realized in the frame of a series of international projects. New information about geoelectrical structures of the crust in Northern Europe and Ukraine was obtained by deep electromagnetic soundings involving controlled powerful sources. An influence of the crust magnetic permeability on the deep sounding results was confirmed.

Electromagnetic soundings across the Holy Cross Mountains, Poland

Semenov V. Yu., Jankowski J., Ernst T., Jóźwiak W., Pawliszyn J., Lewandowski M.

Acta Geophysica Polonica

1998

Vol. 46, nr 2

171-185

Ten deep electromagnetic soundings were performed along the 150 km profile across the southern part of the Tornquist-Teisseyre zone (TTZ) in SE Poland. Five electromagnetic components have been recorded in the period range from few seconds to several hours. The real induction vectors were estimated at all 10 sets, but data from 6 stations only were good enough for magnetotelluric soundings. The magnetovariation data have shown the presence of a high-conductivity, deeply rooted narrow fractive zone of resistivity of about 5 Ohmm, situated in the northern part of Łysogóry unit of the Holy Cross Mountains (HCM). This zone separates two blocks with different geoelectrical properties, particularly well expressed in their upper part. Juxtaposed together with the earlier magnetotelluric (MT) soundings performed east of that profile, the results ofthis study suggest an existence of the easterly extension of the high resistivity zone of the Łysogóry unit far beyond the HCM. If our interpretation accounts for the Carpathian conductive anomaly, a conductive layer within TTZ at the depth of the crust-mantle boundary can be inferred. The mantle conductivity structure for the 2-D modelling was assumed in accordance with results obtained from the Polish geomagnetic observatories Belsk and Hel together with MT deep sounding from Wola Kanigowska.