Lift 2 Palabora—Seismic Hazard Monitoring

Abstract

This chapter takes advantage of the recorded and confirmed as bona fide seismic signature of the Lift 1 caving process for monitoring the Lift 2 caving process and related seismic hazard. A detailed and specific proposal how to monitor and report these matters is given. Methods for Lift 2 seismic hazard estimation are easy to list. What more the probability that they will be successful is high. This is due to the fact that the sources of Lift 2 seismic hazard are known because of Lift 1 experience. As always with nature there will be some unknown factors that will influence the Lift 2 seismic hazard. In nature nothing happens twice in exactly the same way. For this reason it must be expected that the seismic hazard history of Lift 2 might not be exactly as it was in case of Lift 1. There will be differences due to the increased depth of Lift 2 extraction level, which will be located 1600 m below the surface. This should result in higher energy release rates and consequently in increased seismic risk. This is not certain as in the early stage of the caving process the induced seismicity is strongly related to the production rates. In case of Lift 2 it is easy to figure out that the initial production rates and their increase with time will be different to these of Lift 1. On the other hand half of the recorded to date seismicity took place in the rock mass volume that will be Lift 2 cave. This seismicity has preconditioned this rock mass volume. Preconditioning decreases the seismic risk. In case of Lift 2 increased depth will increase the seismic risk while preconditioning will decrease this risk. The question remains in what proportions?