Nikolay Palshin

Electromagnetic images of the deep structure of the Trans-European Suture Zone beneath Polish Pomerania

A large-scale international electromagnetic experiment has been carried out in northwest Poland and northeast Germany. The main goal was to study the deep conductivity structure across the Trans-European Suture Zone, which is the most prominent tectonic structure of Phanerozoic age in Europe. Electromagnetic measurements were carried out mainly along seismic profiles P2, LT-7, and LT-2 crossing the suture zone and running in the northeastern direction. Strike and dimensionality analyses indicate that a geoelectrical strike of N60 degrees W common to both profiles LT-7 and P2 can be estimated. This strike direction was used to project and rotate all transfer functions and both profiles were subjected to 2D inversion using three different approaches. The results show the presence of highly conductive Cenozoic-Mesozoic sedimentary cover reaching depths up to 3 km. A significant conductivity anomaly beneath the central part of the TESZ, called the Central Polish Anticlinorium, has been well resolved at midcrustal depths. The upper mantle of the Precambrian East European Craton is more resistive than, adjacent to the West, the younger Paleozoic Platform.

Probing electrical conductivity of the Trans-European Suture Zone

The Trans-European Suture Zone (TESZ) is the largest tectonic boundary in Europe, crossing northwest-southeast through central Europe from the North Sea to the Black Sea. More than 2000 kilometers long, it constitutes a complex transition between the thick and cold East European Craton (EEQ/Baltic Shield, created more than 650 million years ago (Ma) during the Precambrian, and the warmer, younger Paleozoic (650 to 250 Ma) central European mobile belts.

Studies on the lithosphere and the water transport by using the Japan Sea submarine cable (JASC): 1. Theoretical considerations

The Japan Sea Cable (JASC) was retired from telecommunications services and its ownership transferred to the scientific community in February, 1996. For the first stage of its scientific reuse program, a Japan-Russia joint project has been initiated to monitor electrical potential differences across the Japan Sea to study the electrical conductivity distribution in the Earth and the water transport across the cable.This paper describes preliminary investigations by forward modelling study to explore possible results from the voltage observation, before analyzing real data. On the resistivity structure, modelling has suggested that voltage data is most sensitive to the conductance of resistive lithosphere, especially at longer periods. Water transport modelling has shown that the heterogeneity of sub-bottom resistivity does not greatly influence the cable voltage, and that water transport of 5–6 Sv in the Japan Sea can generate voltage differences of 70–80 mV across the JASC. A preliminary observation was found to be roughly consistent with this estimation.

Compilation of 3D global conductivity model of the Earth for space weather applications

We have compiled a global three-dimensional (3D) conductivity model of the Earth with an ultimate goal to be used for realistic simulation of geomagnetically induced currents (GIC), posing a potential threat to man-made electric systems. Bearing in mind the intrinsic frequency range of the most intense disturbances (magnetospheric substorms) with typical periods ranging from a few minutes to a few hours, the compiled 3D model represents the structure in depth range of 0–100 km, including seawater, sediments, earth crust, and partly the lithosphere/asthenosphere. More explicitly, the model consists of a series of spherical layers, whose vertical and lateral boundaries are established based on available data. To compile a model, global maps of bathymetry, sediment thickness, and upper and lower crust thicknesses as well as lithosphere thickness are utilized. All maps are re-interpolated on a common grid of 0.25×0.25 degree lateral spacing. Once the geometry of different structures is specified, each element of the structure is assigned either a certain conductivity value or conductivity versus depth distribution, according to available laboratory data and conversion laws. A numerical formalism developed for compilation of the model, allows for its further refinement by incorporation of regional 3D conductivity distributions inferred from the real electromagnetic data. So far we included into our model four regional conductivity models, available from recent publications, namely, surface conductance model of Russia, and 3D conductivity models of Fennoscandia, Australia, and northwest of the United States.

Preface to the Special Issue on “The 20th Electromagnetic Induction Workshop”

Electromagnetic (EM) induction methods are used and continue to be developed for a wide range of applications, ranging from exploration near the Earth’s surface to investigations of the deep mantle. In this research, important scientific and societal challenges, such as to search for hydrocarbons and other Earth resources, to probe the structure and dynamics of the lithosphere, to study environmental issues and to monitor and mitigate natural hazards, are addressed. The Working Group I-2 of the International Association of Geomagnetism and Aeronomy on ‘‘Electromagnetic Induction in the Earth’’ has held, since the Edinburgh, United Kingdom, Workshop of 1972, biennial workshops. Here, selected topics are extensively explored by the participants, in the form of oral and poster presentations and discussion sessions. An essential and important part of the EM Induction Workshops (EMIWs) has been the invited review presentations on themes selected by the program committee. These themes vary from workshop to workshop; usually, they highlight recent advances in the rapidly evolving fields of electromagnetic induction and introduce important new directions of research as well as highlight and review results focusing on certain geological targets. The review papers presented at the workshops have traditionally been published as Special Issues of Surveys in Geophysics/Geophysical Surveys since the 1978 workshop in Murnau, Germany. This Special Issue of Surveys in Geophysics contains expanded articles from six review papers presented at the 20th Workshop on Electromagnetic Induction in the Earth (http://mtnet.dias.ie/workshops/2010_Giza/website/index.html). The Workshop was held

LOW ELECTRICAL RESISTIVITY AND SEISMIC VELOCITY AT THE BASE OF THE UPPER CRUST AS INDICATOR OF RHEOLOGICALLY WEAK LAYER

Conductivity models were compiled in two geological provinces with thinsediments. The first province is the margin of the Precambrian East EuropeanPlatform. The second one is the Phanerozoic Rhenish Massif as a part of CentralGermany Hercinicum. In both provinces, a conducting layer was revealed at thebase of the upper crust by the magnetotelluric soundings. Its depth is around10 km in the East European Platform and around 15 km in the Rhenish Massif.The conductance of the layer reaches a few tens of Siemens in the first provinceand is almost an order of magnitude greater in the second one.A good correlation between the conductor and a seismic wave-guide (low-velocityzone) exists at the base of the upper crust. Simultaneous decrease of both electricalresistivity and seismic velocity, suggests an increase of porosity and permeability inpresence of saline water. The depth of rheological weak layer in the PhanerozoicRhenish Massif corresponds to the commonly accepted depth of the thermallyinduced brittle/ductile transition. Contrary similar layer in the Precambrian EasternEuropean Platform is much shallower than the thermally induced transition. Somenew mechanism should be considered.

Measurements of motinally induction voltage in the Ria de Aveiro lagoon (Portugal)

Techniques based on motional induced voltage (MIV), which is induced by the water flow across Earths magnetic field has motivated and increase of interest of oceanographers, regarding studies of large scale ocean flows. The major part of these experiences has been applied to large-scale ocean studies. This technique has been demonstrated during last decade to provide reliable information when applied to the flow monitoring in large oceanic channels. In this paper we present the preliminary results of the implementation of these techniques to smaller scales systems like the one of Ria de Aveiro lagoon (Portugal). A submarine cable crossing the channel at the entrance of the lagoon (Barra channel) allows the estimation of the water flow at this place. The preliminary analysis of the collected data shows that there is a good potential to obtain the water transport (by tidal and residual flows) through the canal by measuring the differences of electrical potential.

Long-term electromagnetic field observational network in Russian Primorye

An electromagnetic field observational network is being constructed in Russian Primorye. The method employs a commercial telephone network to measure voltage differences with long dipole lengths ranging from 10 to several dozens of kilometers. For better understanding of the spatial and frequency behavior of transfer functions a prognostic model of 3D conductivity structure has been constructed and the numerical modeling has been carried out. The particular aim is to check the hypothesis that the lithospheric mantle is much more resistive that is was estimated using a homogeneous model of the lithosphere and the low values of effective integral resistivity were obtained due to the influence of the sub-vertical conducting zones associated with subduction system.