Present-Day Seismicity in Bohemian Massif: Looking for Similarities in Two Most Seismoactive

PRESENT-DAY SEISMICITY IN BOHEMIAN MASSIF: SIMILAR FEATURES OF TWO MOST SEISMOACTIVE REGIONS.

P. Špaček, J. Pazdírková, V. Nehybka , R. Tilšarová

1 Institute of Physics of the Earth, Faculty of Science Masaryk University, Tvrdého 12, 602 00 Brno, Czech Republic, Tel.: +420 543 423 116, FAX: +420 543 423 120, e-mails:

Two seismically most active regions within the Bohemian Massif are located at opposite margins of the massif and are separated by a domain of very low seismicity. Despite the different tectonic position, some important geological features are similar and characteristic for these two regions only. In the Western Bohemia/Vogtland region the occurrence of earthquake swarms, each comprising several thousands of events, is characteristic. The epicentres are distributed in several groups, the major of which has a marked linear shape with NNW-SSE orientation. Predominance of strike-slip movements is documented by focal mechanisms. In the NE Bohemian Massif (Eastern Sudetes) the seismic activity is distributed over larger area within a mesh of NW-SE to NNW-SSE striking faults. Focal mechanisms indicate strike-slip movements on NW-SE oriented structures. The number of registered earthquakes is much smaller and the recurrence periods are larger, nevertheless, in many cases the swarm-like nature of earthquakes can be observed, too. It seems that in both regions faults suitably oriented to stress tensor are present. However, such faults can be found in many places throughout the Bohemian Massif where no seismic activity is observed. Typical for both seismoactive regions is the occurrence of Pleistocene volcanism and abundance of CO2 emissions and carbonated mineral springs. It is tempting to link the seismicity and post-magmatic activity in both regions. However, it is not possible to exclude that the regional weakening of the crust is a primary cause for seismicity, the post- magmatic activity being only another result of the weakening. In our contribution a discussion is opened about the possible causal links between the increased seismic activity and local geological conditions. - seismicky nejaktivnější oblasti, historicky i dnes - počty registrovaných jevů, magnituda - časová distribuce, rojový charakter - prostorová distribuce ohnisek, jejich vazba na SZ-JV až S-J orientované struktury - fokální mechanismy, napětí a vhodná orientace zlomů - prostorová shoda s kvartérním vulkanismem - shoda s emisemi CO2