The western part of the Bohemian Massif (Vogtland/West-Bohemia region at the Czech-German border) is characterized by relatively frequent intraplate earthquake swarms and by other manifestations of current geodynamic activity, such as mofettes, mineral and thermal springs. In this study we analyze variations of groundwater level in four hydrological wells in the region during the years 2005-2010. Monitoring during the previous time interval of 2000-2004 is also mentioned and used for comparison. Two of the wells are located in the epicentral region of Nový Kostel, and the other wells are more distant. The time interval includes the 2008 earthquake swarm when all the wells displayed a noticeable drop in the water level. This effect was observed up to epicentral distances of nearly 30 km, which exceeds the distances of hydrological changes observed during previous earthquake swarms. Moreover, it seems that a small rise in the water level preceded the intervals of increased seismic activity, which could represent a certain precursory phenomenon. On the other hand, the hydrological changes in the Nový Kostel area were relatively small, indicating that this epicentral area is not hydrologically linked with the seismically active fault at depth. Consequently, more suitable localities for hydrological monitoring should be sought in a broader vicinity of Nový Kostel., Renata Gaždová, Oldřich Novotný, Jiří Málek, Jan Valenta, Milan Brož and Petr Kolínský., and Obsahuje bibliografii
Local seismicity of the Hronov-Poříčí Fault Zone is studied using two-year continuous seismic data from four seismic stations in the area. Newly developed software for automatic seismic events detection is introduced - it is based on the method used at the Icelandic seismic network. Twelve major local earthquakes are detected, localized and their magnitudes are estimated. Simultaneously, groundwater levels are continuously monitored in three wells in the area. Multiple-filtering method, originally used for processing of broadband and dispersed seismic signals, is modified and used for the frequency-time analysis of the water level data. Dominant tidal influence on the groundwater level variations is shown. Theoretical tidal potential for all three well locations is computed. Groundwater data and tidal potential are bandpass filtered to focus on the semidiurnal periods. Mutual amplitude ratio and phase shift between both quantities are computed. Each of the three wells exhibits different pattern of the groundwater level variations with respect to tides. A distinct change in the phase shift is observed at the VS-3 well in the second half of 2009. In the same time span, increased seismic activity is also observed. However, other two wells do not exhibit any evidence of such phase shift. Detailed groundwater level data analysis does not prove any significant rises or drops of the groundwater levels in 28 day intervals around the detected local events. In contras t, unexplained groundwater level drop in the V-34 well is obser ved 18 hours before the teleseismic Tohoku earthquake, Japan, March 11, 2011, Mw = 9.0., Petr Kolínský, Jan Valenta and Renata Gaždová., and Obsahuje bibliografické odkazy
Rayleigh waves in the period range 0.2 - 3.0 s from eight quarry blasts are analyzed to obtain S-wave velocity model beneath the Příbram seven-station array in the Czech Republic. Locations and origin times of blasts are estimated using P- and S-wave onsets and then verified at the quarry in the vicinity of the location. This blind test confirms a sufficient precision of the location procedure for identification of quarries. Epicentral distances are in the range from 16 to 52 km. Group velocity dispersion curves of Rayleigh waves are determined by the frequency-time analysis. An average group velocity beneath the array for each period is computed with the help of mean travel-time curve for all blasts and stations. The resultant group velocity dispersion curve is inverted to obtain a 1-D S-wave velocity model using the Isometric method. The results are compared with known geological structure in the area of interest., Renata Gaždová, Petr Kolínský, Jiří Málek and Jan Vilhelm., and Obsahuje bibliografii