Measurements for determining the safety against earthquakes of abandoned shafts for radioactive waste disposal

In view of the various sites currently envisaged for ultimate storage in the Eastern region of Lower Saxony, at two of these sites underground seismometer measurements for estimating the seismic risk have been carried out. The digitally recording stations are described, and the ground unrest which is much more favourable compared with sites above ground, is demonstrated by means of spectra and a presentation of the detection threshold. A considerable obstacle in interpreting the events is the unsatisfactory discernability of natural and artificial shocks (explosions). Nevertheless it can be said with a probability of approximately 60 per cent that from January 1980 until May 1982, apart from a minor event, there were no seismic activities in the Eastern part of Lower Saxony. Reservations must be made for the area of Gorleben located a bit farther where a detection threshold of M(L) = 1,7 to 2 is to be taken into account. (orig./HP)