Václav Červ

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.

Numerical solution of the two-dimensional inverse geomagnetic induction problem

SummaryAn effective numerical approach to the solution of the two-dimensional inverse geomagnetic induction problem using the linearization method is presented. The numerical realization of the inversion is based on Marquardts algorithm, for which the solution of the direct problem and the partial derivatives of this solution with respect to the electrical parameters of the medium are computed by the finite difference method. Theoretical models are studied and numerical results are presented.

Anomalous induction in the Carpathians

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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.

Numerical modelling in laterally inhomogeneous geoelectrical structures

РезюмеИзлaaеmся чuсленныŭ меmо¶rt; мо¶rt;елuровaнuя элекm ромaнumных nолеŭ Н- u Е-nолярuзaцuŭ в ¶rt;вумерно нео¶rt;норо¶rt;ных сре¶rt;aх. Обсуж¶rt;aюmся uсmочнuкu ощuбок, коmорые моуm вознuкamь в nрuмененuu меmо¶rt;a конечных рaзносmеŭ в уVлaх соnрuкосновенuяеоэлекmрuческuх nо¶rt;облaсmеŭ с рaзлuчaющuмuся элекmрuческuмu nрово¶rt;uмосmямu.

Resolution of anisotropic and shielded highly conductive layers using 2-D electromagnetic modelling in the Rhine Graben and Black Forest

Abstract Anisotropy in magnetotelluric (MT) data has been found very often and has been explained as the result of local structures of different conductivities. In this paper, an observed anisotropy in MT data is not interpreted qualitatively in terms of local structures but is modelled quantitatively by a quasi-anisotropic layer. Besides the MT transfer functions, measurements of the vertical magnetic component are required. The second goal of this paper is to describe a method which permits the resolution of mid-crustal conductive layers in the presence of an additional high-conductivity layer at the surface. This method is possible in a two-dimensional (2-D) situation that limits the spatial extension of the surface structure. Again, vertical magnetic field recordings are necessary, but the phase of the E-polarization with respect to the 2-D structure is the most sensitive parameter. Using two field sites in Southern Germany, it has been possible to give a quantitative explanation of anisotropy and an improved depth resolution, and to derive an integrated conductivity of the highly conductive mid-crustal layers using MT and geomagnetic depth sounding data. The anisotropic highly conductive layer is located 12 km beneath the poorly conductive Black Forest crystalline rocks, whereas it is at a depth of 6 km beneath the highly conductive Rhine Graben sediments.

Solution of the one-dimensional inverse magnetotelluric problem

SummaryMethods of solving the inverse magnetotelluric problem are compared. Basic relations for Newtons method, the least-squares method and Marquardts method are presented and the convergence properties of these methods are studied. The high effectiveness of Marquardts method is demonstrated and its application to practical magnetotelluric data is discussed.

A magnetotelluric profile across the German Deep Drilling Project (KTB) area: Two‐ and three‐dimensional modeling results

Previous interpretations of magnetotelluric data from the vicinity of the German Deep Drilling Project (KTB) revealed two major structures: a midcrustal layer of increased conductivity and large, regional extent and a highly anisotropic upper crust. Nevertheless, a satisfactory combination of both structures explaining all measurements has not yet been achieved, mostly due to incomplete and qualitatively poor data. Simplified superposition of both structures could not yield an explanation of the observations. On the basis of a carefully processed new data set we apply different modeling approaches to verify the existence of both structures. Models calculated with a two-dimensional modeling program, which allows for general anisotropy, as well as a full three-dimensional code show that an anisotropic upper crust is overlaying a regional east-west striking high-conductivity structure. Nevertheless, this continuous conductive midcrustal layer with a conductance decreasing from north to south must be replaced by a quasi-anisotropic one, at least in the region of the KTB. The final model may still be oversimplified, considering the complexity of the true but unknown geology in this particular area, but it demonstrates which major electrically effective structures could be resolved.

Electromagnetic measurements in the vicinity of the KTB drill site. Part II. Magnetotelluric results

SummaryIn addition to the magnetovariational measurements across an array in Western Bohemia, close to the KTB ultradeep borehole (Germany), discussed in part I of this paper [1], magnetotelluric results from pivot sounding point Ostrůvek within the array are presented here. Good quality of long-period magnetotelluric data (period range from 30 s to about 1 hour) allowed structural dimensionality of the medium to be analysed in detail. The geoelectrical structure was identified as a slightly distorted two-dimensional regional substratum, with dominating E - W strike, overlaid by a heterogeneous subsurface layer with extremely strong and anisotropic galvanic distortion effect on the magnetotelluric data. Estimating the total static shift distortion tensor by fitting the local magnetotelluric curve to the curve of the global magnetovariational soundings (for the European continent), the static distortions were identified as of generally multidirectional origin. The resulting telluric ellipse is, however, strongly anisotropic, indicating an approximately SW - NE apparent local strike, which is in the approximate agreement with remote reference magnetovariational results. Finally, the magnetotelluric results from the station Ostrůvek are compared with long-period data from the immediate neighbourhood of the KTB borehole on the German territory.

Mt-field of H-polarization in models with dipping interfaces

РезюмеПрuво¶rt;umся решенuе ¶rt;ля расnре¶rt;еленuя элекmроманнumноно nоля Н-nолярuзацuu на мо¶rt;елu слоuсmоŭ норuзонmально нео¶rt;норо¶rt;ноŭ сре¶rt;ы с наклонным конmакmом. Сuсmема разносmных уравненuŭ решаеmся релаксацuонным меmо¶rt;ом.