Geophysical Field Pattern in The West Bohemian Geodynamic Active Area

Regional geophysical data from detailed gravity survey, airborne magnetometry and gamma-ray spectrometry were analysed in order to determine the subsurface extent of contrasting geological bodies and to highlight subtle anomalies which can be related to the occurrence of earthquake swarms. Potential field data were compiled into contour and colour-shaded relief maps suitable for detecting structural tectonic elements. A shaded relief map of the horizontal gradient of gravity was used to detect considerable structural and tectonic features. The results of airborne gamma-ray spectrometry, showing the regional total gamma-ray activity, abundance of uranium, thorium and potassium, were included in this study. Only the two most instructive maps – the total gamma-ray activity and the abundance of potassium are shown. The main line of epicentres Nový Kostel – Poátky coincides well with the N-S configuration of abundances of these natural radioactive elements. The epicentres of micro-earthquakes detected by the local seismological network KRASLICE for the 1991 to 1998 period were plotted in the geophysical maps. The hypocentres of earthquakes in the main epicentral zone at Nový Kostel were projected onto the crustal density model based on the interpretation of seismic reflection profile 9HR and gravity data. The average distance between the Nový Kostel epicentral zone and the seismic profile was 4-5 km. Based on the interpretation of gravity data the hypocentres of the main epicentral zone seem to be associated with the western margin of the Eibenstock - Nejdek (Karlovy Vary) Pluton and, beside that, they follow the depth level where the allochthonnous part of the Saxothuringian Zone is thrust over the European parautochton. A drawing of the geodynamic model of the area is also shown.     

Slope movements in the Flysch Carpathians of Eastern Czech Republic triggered by extreme rainfalls in 1997: a case study

The severe rainfalls in Northern and Central Moravia and Eastern Bohemia in July 1997, triggered slope movements recorded particularly in the flysch-type rocks of Northern and Eastern Czech Republic. The basis of the diversified woodland and agricultural landscape of the Western Carpathians is the highland and mountain erosion–denudation and structure-denudation relief, which consists of flysch rock complexes. The geomorphological and geological setting is predisposed to extensive slope deformations––especially landslides. Slope movements play an important role in topography modelling and cause great direct and indirect damages in the countryside as well. Slope deformations of different intensity and aerial extent control the character of relief on the local or regional scale. Significant changes of land use may result from the slope movements, especially when the reclamation of the slope deformations are not undertaken. Landslides themselves have a great impact on the water regime of the landscape and consequently on the development of ecosystems. That is why they are often considered to be a significant biodiversity factor. It is also necessary to pay attention to the opposite effect since the land use (dispersed woody patches, landscape mosaic) is to a certain extent influencing the development and progress of the slope deformations. Based on the order we focused our geological investigations on the area in which the slope movements began to develop to such an extent that human lives and properties were considerably endangered. The total damages from activated landslides reached about 40 million USD. The landslide research differs in individual localities and their topical situations and is accompanied by a stability assessment of the locality and a proposal of rescue measures. An alternative solution should consist of an assessment of necessary changes in the area plans of affected villages, prospects of their future habitability, and displacements of engineering networks and roads.