Overview of the Geophysical Monitoring Activities on the Hard-Rocks in Czechia

Summary The process of the site selection in Czechia includes two main parts of the geophysics-related activities: geophysical field campaigns at the potential sites for geological setting´s characterization and monitoring works at the natural analogues of the future deep geological repository. Contrary to the approach of other countries regarding a suitable geological formation for the repository, Czech Republic sticks to the Scandinavian model, i.e. assumes the hard-rock formations as the most suitable host rock. Within approximately last decade two main test analogue sites have been used for multiple monitoring activities in the country – Bedřichov granite gallery and URF (underground research facility) Bukov, set in paragneisses and amphibolites. Multi-year geophysical monitoring using the SGI 1 system has been carried out at both sites, using mainly electrical resistivity tomography (ERT) and ultrasonic seismic measurements directly on the walls of the galleries. The repeated measurements showed that relatively weak natural phenomena influence the near-surface zone of the massif, e.g. the ventilation regime in the gallery. No variations in the state of stress of the massif have been observed on the seismic data.