ABSTRACT:

Knowledge of stress strain fields and their development is fundamental for all mine working and for its proper planning. A model of the recent stress fields in the Czech part of the Upper Silesian Coal Basin (USCB) has been interpreted. Stresses causing Variscan structural tectonic pattern in the USCB, based on paleostress analyse, have been used for the starting point of the research project. It was taken into account the influence of Alpine deformation due to Carpathian nappes. There were more stress tensor gauging realised for recent stress state determination in the region above all using hydrofrac and treated overcoring methods during last ten years. It's becoming apparent that for information of recent stress fields is usable the interpretation of focal mechanisms of energetic significant mine induced seismic events, which were observed here more than ten years. The aim of the project is the verification the dependence and influence recent stress on original stress state presented by paleostress model compiled and based on structural tectonic interpretation. In this contribution there are presented the results and their conclusions obtained up to now.

1 GEODYNAMIC MODEL OF THE USCB BASED ON PALEOSTRESS ANALYSIS

The Upper Silesian Coal Basin (USCB) corresponds to the apical domain of the Variscan accretion wedge (foreland coal-bearing molasse),which is nowa part of the epi-Variscan basement, representing northwestern foreland of Alpine orogeny belt (Fig. 1). The Variscan fold and thrust structures of the Moravosilesian zone, striking NNE-SSW with generally eastward vergency and principally corresponds to W-E oriented compression. A very significant role, from the point of view of Variscan tectonics, is played by the Brunovistulian foreland (Precambrian terrane consolidated in the time of Cadomian orogeny). Diagram of Variscan stress-strain model is presented on Figure 2. Recently the USCB is located in immediate foreland of Western Carpathian nappes.

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