Abstract
Long-term monitoring of the rock massif using geophysical methods is carried out in the area of the Underground Research Facility (URF) Bukov, Czech Republic. Changes in apparent electrical resistances on the mine wall are monitored using the Electrical Resistance Tomography (ERT) method. 48 electrodes are used on the profile with a step of 25 cm.
The repetition frequency was in the test phase 8 times a day, in the monitoring phase it is measured once a day. High-frequency active seismic measurement uses one seismic source and three receivers at distances of 30, 60 and 90 cm from the source.
The measurement is performed 4 times a day. The length of monitoring series is currently over 2 years.
It was found that the measured quantities show a weekly periodicity of changes, which is related to the ventilation regime in the mine. Due to periodicity in ventilation regime, the periodical changes in temperature (by approx. 1-2 °C) and humidity (by approx. several %) are observed during some time intervals.
Under the given circumstances, these changes lead to clearly measurable changes in the apparent resistivities of the rock mass and at the same time to changes in the amplitudes and frequencies of seismic waves. Based on the analysis of the S-coda waves of high-frequency active seismic measurement, it can be concluded that this is not just a near-surface effect, but changes in the rock mass affect a larger volume of rocks in the vicinity of the underground excavation.