The use of caves as observatories for recent geodynamic activity and radon gas concentrations in the western carpathians and bohemian massif

In recent years, many underground spaces such as caves and deep mines have been used to monitor geodynamic activity in the Western Carpathians and Bohemian Massif. In addition, long-term radon gas monitoring has also being undertaken in three of the caves. The observed radon concentrations have shown diurnal, seasonal and yearly variations. A significant correlation with external temperature has been registered. This pattern is considered to result from the movement of air caused by the contrast between the broadly constant internal and fluctuating external temperatures. The same seasonal effects have been observed in the record of active fault displacements at sites close to the surface. These seasonal effects lead to peak-to-peak massif dilation amplitude that affects the overall trend of fault displacement. It is also noted that a significant decrease in this amplitude occurs with increasing depth beneath the surface. However, high variability has also been observed in both the radon concentration and fault displacement activity recorded. Many events have been registered that link these two geofactors. (authors)