Magnetotelluric investigations of the seismically active region of Northwest Bohemia: preliminary results

Abstract

During 1997, within the framework of an Italian-funded scientific cooperation between Italy and the Czech Republic, a series of magnetotelluric (MT) soundings was carried out in the region of Northwest Bohemia (Czech Republic). This is one of the most seismically active areas in Central Europe, where micro-earthquake swarms frequently occur during the apparently quiescent intervals between large macro-seismic swarms. Fifteen MT stations were installed in an area of about 15 ´ 20 km2 where 80% of the seismicity of the entire region has been recorded since 1986. The area showed a high electromagnetic noise, possibly of high cultural origin from the nearby industrial zone of the Sokolov basin, which affected both the electric and the magnetic signals. The final data, carefully selected, were modeled by 2D and 3D techniques. The results show an extensive conductive structure in the depth range from 0.5 to 3 km. This structure could be connected with the locally buried granitic massif in the inhomogeneous metamorphic basement, probably accompanied by fracturation, thermo-metamorphism or paleofluids. Moreover, the presence of a conductive anomaly in the northern part of the investigated region could be linked to a lithological change in the metamorphic rocks (prevalence of phyllites over mica schists), which would even increase the effect of the granite.