Investigation of relationships in time-domain between tectonic and tidal signals observed in the Geodynamic Laboratory of SRC and seismic events which occur in the Middle Odra Faults Zone (The Lower Silesian copper mining region)

Since plenty of years the measurements carried out in the Geodynamic Laboratory of SRC PAS provide us with numerous observations of vertical motions and tiltings of foundations which are suitable for studies of tectonic signals. These signals are produced by the recent tectonic activity of the Sudetic and adjacent areas. The Geodynamic Laboratory is situated in the middle of geological unit called Swiebodzice Depression. The laboratory is distant about 40 km from the Fore-Sudetic Monocline and the Middle-Odra Faults Zone. The Middle-Odra Faults Zone is seismically active. The strongest events which occurred there reach maximally 5.5 [deg] in the energetic scale. The system of active faults cuts through the copper mining region and produces seismic hazard. Closeness of the Geodynamic Laboratory to this area creates good opportunity to investigate dependencies between variations of kinematic activity of Swiebodzice Depression orogen and seismic activity of the Middle-Odra Faults Zone. On the base of almost 10 years long measurements we found relations between velocities of rocky blocks displacements in the Swiebodzice Depression and occurrences of seismic events in the Middle-Odra Faults Zone. The possibility of measurements of the level of kinematic activity of the massif (velocities of motions) results from the location of the long water-tubes and pendulums on the system of faults well visible in the underground corridors of the Ksiaz Geodynamic Laboratory. We observed that during 10 years almost all the seismic events took place when the first derivative was close to zero which represents the pause in kinematic activity of the massif and the stop of relative displacements of blocks. This observation suggests that the large dimension filed of tectonic pressure appeared simultaneously in the Swiebodzice Depression and the Fore-Sudetic Monocline and that the seismic events occur during the extension phase rather than the compression phase. Revealed the second correlation was unexpected. Through dozen or so days almost all the earthquakes happened accordingly to a certain rule, i.e. during the similar phase of tide. Next, the rule was changed and through the dozen or so days the earthquakes occurred during a different but also constant phase of tide. Observations of kinematic activity of the orogen of Swiebodzice Depression can be used as the indicator of evaluation of probability of seismic hazard in the Lower Silesian copper mining region.

Keywords: geodynamics, tectonic activity, mine surveying, tectonics of the Sudetic Mountain region, geodetic and geophysical measuring systems