The Present State of Art of Long Period Magnetotellurics in the Western Part of the Bohemian Massif

Abstract

Research into the complex geological structure of the Middle European Variscides in the western part of the Bohemian Massif has largely intensified in connection with the KTB deep borehole project in the Oberpfalz, Germany. First results of long period magnetotelluric studies along an about 100 km long profile in SW Bohemia, close to the KTB drilling site, are presented here. They represent a partial step within a broader project of constructing a 3-D geoelectrical model of the western margin of the Bohemian Massif and resolving the relations of anomalous geoelectrical features to the geological structures of the region. The data roughly fit a composite model of a 2-D regional structure, striking E-W, overlaid by a layer of highly distorting near-surface inhomogeneities. The distorting layer displays large anisotropy with preferred conductivity in NW-SE to NNW-SSE direction. Attempt is made to estimate the absolute static shift of the MT curves. Several variants of 2-D models for the deep regional structure are discussed, including an anisotropic model which can qualitatively explain the discrepancy of the principal directions indicated by the MT and GDS data. The relation of the results obtained along the particular profile to the regional geoelectrical background is studied.