Seismo-hydrological monitoring in the area of the Hronov-Poríčí Fault Zone, Northern Czech Republic, Central Europe
Abstract
The Bohemian Massif - the Central European Variscan structure - is an area with a weak intraplate seismicity. Only its marginal parts are affected by young (up to Early Quaternary) tectonic movements responsible for uplift of mountain chains on the borders. A part of this natural boundary is the Hronov-Poríčí Fault Zone (HPFZ) on the NE of the Czech Republic. The HPFZ is a result of long-lasting evolution since the late Paleozoic with several tectonic phases. The contemporary HPFZ consist of a main reverse fault (thrust) accompanied by parallel or oblique normal or reverse faults. The seismic activity of broader area of the HPFZ - a proof of present day mobility of the area - is characterized by relatively frequent local earthquakes. The strongest earthquake in January 1901 reached the magnitude of 4.6. Another proof of the mobility is a presence of CO2-rich mineral springs in the area. The seismic activity of the area is monitored by four seismic stations - CHVC, DPC, OSTC and UPC. They are equipped with broadband seismometres and the sampling frequency is 100 or 250 Hz. A methodology for automated picking of local event arrival times (similar to STA/LTA ratios plus requirement for a candidate event to be located on certain number of stations) was developed to enable us processing of large datasets. The recorded data are automatically scanned for possible local earthquakes which are then reviewed by seismologists and further processed. This procedure increased the number of detected events more than twenty times. Hydrological changes are monitored in three boreholes by water-level sensors. The sensors take readings every 10 minutes. The air pressure values are recorded every hour. The ground water levels obviously follow the seasonal changes in aquifers which are replenished after heavy rains and snow melting. However, distinct step-like water level changes (rise +6 and +15 cm) were observed on one of the wells before the 2005 earthquakes (M = 2.4 and M = 3.3). The first one was observed 11-15 hours before the event while the other one was observed 29-32 hours before the earthquake. We interpret this behavior as a possible precursory phenomena.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.S11B2211V
- Keywords:
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- 7223 SEISMOLOGY / Earthquake interaction;
- forecasting;
- and prediction;
- 7230 SEISMOLOGY / Seismicity and tectonics