E. D. Tereshchenko

Deep electromagnetic sounding of the lithosphere in the eastern Baltic (fennoscandian) shield with high-power controlled sources and industrial power transmission lines (FENICS experiment)

The paper addresses the technique and the first results of a unique experiment on the deep tensor frequency electromagnetic sounding, the Fennoscandian Electrical conductivity from results of sounding with Natural and Controlled Sources (FENICS). In the experiment, Energy-1 and Energy-2 generators with power of up to 200 kW and two mutually orthogonal industrial 109- and 120-km-long power transmission lines were used. The sounding frequency range was 0.1–200 Hz. The signals were measured in the Kola-Karelian region, in Finland, on Svalbard, and in Ukraine at distances up to 2150 km from the source. The parameters of electric conductivity in the lithosphere are studied down to depths on the order of 50–70 km. A strong lateral homogeneity (the one-dimensionality) of a geoelectric section of the Earth’s crust is revealed below depths of 10–15 km. At the same time, a region with reduced transverse crustal resistivity spread over about 80 000 square kilometers is identified within the depth interval from 20 to 40 km. On the southeast the contour of the anomaly borders the zone of deepening of the Moho boundary down to 60 km in Central Finland. The results are compared with the AMT-MT sounding data and a geodynamic interpretation of the obtained information is carried out.

A set-up converter and energy transfer system of an “Energy-2” generator for electromagnetic sounding and monitoring of zones of earthquake sources

A boost converter and a system of energy transfer at a high voltage (up to 1100 V) developed for an “Energy-2” generator 200 kW in power are described. This generator is intended for solving the problems of precision monitoring of the electromagnetic depth of the Earth’s crust at seismoactive regions with an aim to search for earthquake forerunners. High voltage allows taking off the total generator’s power on transmitting antennas with high resistance (7 Ω and higher) within a wide frequency range (0.1–200 Hz) as well as on low-resistance antennas (lower than 0.7 Ω) at high frequencies (greater than 20 Hz). Modern Russian and foreign literature on the problem of developing transformers and rectifiers of the generator’s power circuit, responsible for generation of powerful low-frequency electromagnetic signals, is reviewed. Theoretical research and numerical simulation of the “Energy-2” generator’s power circuit are performed and the element base of the latter is optimized. Based on the developed documentation of all components, radiators and a system of forced ventilation have been made. The proposed generator-measuring complex has no analogs in world practice and can be used for solving a wide range of fundamental and applied problems.

Effect of the ionosphere on electromagnetic waves from ground-based emitter in the frequency band 1–10 Hz

The results of the first experimental reception of electromagnetic signals, emitted by the ground antenna at frequencies of 1–10 Hz in the transition zone in the case when the distance from the transmitter is comparable with the equivalent waveguide height, are presented. The works were performed episodically in 2006, in different seasons and at different time of day, under quiet geomagnetic conditions. A pronounced effect of the state of the ionosphere on the received signal value was found out at distances about 80 km from the transmitter; in this case the seasonal manifestations were more substantial than the daily ones. The obtained results indicate that it is necessary to take into account the effect of the ionosphere on the wave amplitude in the transition zone, when the electromagnetic sounding of the Earth’s structure is performed at frequencies of 1–10 Hz, and that it is reasonable to use artificial waves in this band to perform quasi-vertical sounding of the ionosphere.

Detection of infrasound from the Vitim bolide on September 24, 2002

An infrasonic signal from an atmospheric bolide explosion was detected on September 24, 2002 near the Vitim river, Irkutsk region (57.9 N, 112.9 E). The signal was detected by three spatially separated microbarographs of the Polar Geophysical Institute (PGI), Kola Science Center, Russian Academy of Sciences, Apatity (67.6 N, 33 E) at a distance of 4000 km from the source. The acoustic gravity signal from a falling meteorite at high latitudes was detected at such a distance for the first time in Russia.

International FENICS Experiment on the Tensor Frequency Electromagnetic Sounding of the Lithosphere in the Eastern Baltic (Fennoscandian) Shield

ISSN 1028-334X, Doklady Earth Sciences, 2009, Vol. 427A, No. 6, pp. 979–984.

Transcontinental radio tomographic chain: First results of ionospheric imaging

The results of studying the structure of the ionospheric plasma distribution from data obtained at the transcontinental Russian radio tomographic chain, which is the world’s longest, are presented. The 4000 km long tomographic chain extends from the Svalbard Archipelago to Sochi. The unique feature of this upgraded radio tomographic system is that for the first time observations cover a wide sector of the ionosphere from high latitudes (polar cap and auroral region) to low latitudes. This allows us to study the transfer of perturbations in the system auroral-subauroral-midlatitude-low latitude ionosphere, and to analyze ionospheric electron density distributions in different latitudinal regions as a function of different external factors and solar-geophysical conditions. The first recent results speak for a complex structure of the ionospheric plasma, even in quiet geophysical conditions (Kp < 2.)

Tidal effects in the controlled-source ULF electromagnetic field on the Baltic crystalline shield

The results of the experiment on studying the dynamics of the electromagnetic field (EM) generated by the stationary controlled ULF-band source during 30 days on the Baltic crystalline shield are presented. Diurnal variations in the EM fields and slow variations in the surface impedance with a period of about 14 days are revealed. The diurnal variations in the fields are mainly due to the fluctuations in the ionospheric parameters caused by the changes in the daytime ionization of the ionosphere by solar radiation. By comparing the harmonic component with a period of about 14 days, which was established in the time series of surface impedance, with the slow tidal deformations of the Earth’s crust, we revealed the correlation between the EM variations and tidal processes in the Earth. The estimates for the probable changes induced by tidal deformations in the structure and conductivity of the underlying medium are obtained by modeling.

Features of amplitude and Doppler frequency variation of ELF/VLF waves generated by “beat-wave” HF heating at high latitudes

Observations of extremely low frequency (ELF, 3–3000 Hz) radio waves generated by a “beat-wave” (BW) high frequency (~ 4.04–4.9 MHz) ionospheric heating are presented. ELF waves were registered with the ELF receiver located at Lovozero (68°N, 35°E), 660 km east from the European Incoherent Scatter Tromso heating facility (69.6°N, 19.2°E). Frequency shifts between the generated beat-wave and received ELF waves were detected in all sessions. It is shown that the amplitudes of ELF waves depend on the auroral electrojet current strength. Our results showing a strong dependence of ELF signal intensities on the substorm development seem to support the conclusion that electrojet currents may affect the BW generation of ELF/VLF waves.

Electromagnetic sounding of the Earth’s crust in the region of superdeep boreholes of Yamal-Nenets autonomous district using the fields of natural and controlled sources

Electromagnetic soundings with the fields of natural (magnetotelluric (MT), and audio magnetotelluric (AMT)) and high-power controlled sources have been carried out in the region of the SG-6 (Tyumen) and SG-7 (En-Yakhin) superdeep boreholes in the Yamal-Nenets autonomous district (YaNAD). In the controlled-source soundings, the electromagnetic field was generated by the VL Urengoi-Pangody 220-kV industrial power transmission line (PTL), which has a length of 114 km, and ultralow-frequency (ULF) Zevs radiating antenna located at a distance of 2000 km from the signal recording sites. In the soundings with the Urengoi-Pangody PTL, the Energiya-2 generator capable of supplying up to 200 kW of power and Energiya-3 portable generator with a power of 2 kW were used as the sources. These generators were designed and manufactured at the Kola Science Center of the Russian Academy of Sciences. The soundings with the Energiya-2 generator were conducted in the frequency range from 0.38 to 175 Hz. The external generator was connected to the PTL in upon the agreement with the Yamal-Nenets Enterprise of Main Electric Networks, a branch of OAO FSK ES of Western Siberia. The connection was carried out by the wire-ground scheme during the routine maintenance of PTL in the nighttime. The highest-quality signals were recorded in the region of the SG-7 (En-Yakhin) superdeep borehole, where the industrial noise is lowest. The results of the inversion of the soundings with PTL and Zevs ULF transmitter completely agree with each other and with the data of electric logging. The MT-AMT data provide additional information about the deep structure of the region in the low-frequency range (below 1Hz). It is established that the section of SG-6 and SG-7 boreholes contains conductive layers in the depth intervals from 0.15 to 0.3 km and from 1 to 1.5 km. These layers are associated with the variations in the lithological composition, porosity, and fluid saturation of the rocks. The top of the poorly conductive Permian-Triassic complex is identified at a depth of about 7 km. On the basis of the MT data in the lowest frequency band (hourly and longer periods) with the observations at the Novosibirsk observatory taken into account, the distribution of electric resistivity up to a depth of 800 km is reconstructed. This distribution can be used as additional information when calculating the temperature and rheology of the lithosphere and upper mantle in West Siberia. The results of our studies demonstrate the high potential of the complex electromagnetic soundings with natural and controlled sources in the study of deep structure of the lithosphere and tracing deep oil-and-gas-bearing horizons in the sedimentary cover of the West Siberian Platform within the Yamal-Nenets autonomous district.

Phase Variations of ULF Magnetic Field in the Region of Fault Tectonics

The experiment on phase measurements of three components of a ULF magnetic field generated by a high-power controlled source in the region dominated by fault tectonics is described. The measurements were carried out along two orthogonal directions. It is established that the phase sharply varies by about 180° between some measurement points. The phase jumps are found to be confined to the conductive geological faults, which opens the possibility of locating the faults using the phases of ELF magnetic fields.