Establishment of SATREPS experimental sites in South African gold mines to monitor phenomena associated with earthquake nucleation and rupture

Abstract

Mining-induced earthquakes pose a risk to workers in deep mines, while natural earthquakes pose a risk to everywhere, but especially near plate boundaries. A five year Japanese–South African collaborative project entitled ‘Observational studies to mitigate seismic risks in mines’ commenced in August 2010. Here we report on the achievements of the first 18 months of the project. Faults at Ezulwini, Moab–Khotsong and Driefontein gold mines considered likely to become seismically active during mining activity were modelled using pre-existing geological information supplemented by cores and camera images from new boreholes. As of 30 January 2012, about 90% of about 70 planned boreholes totalling more than 2 km in length had been drilled at project sites to locate fault zones accurately and to deploy sensors. Acoustic emission sensors, geophones, accelerometers, strain- and tilt meters, and controlled seismic sources were installed to monitor the deformation of the rock mass, the accumulation of damage during the earthquake preparation phase, and changes in stress produced by the propagation of the rupture front. The suite of sensors has greater sensitivity and dynamic range than those typically used in civil or mining engineering applications, making it possible to record very small changes in stress and strain as well as violent rock mass deformation associated with large seismic events. These data sets will be integrated with measurements of stope closure, strong ground motion in stopes, and seismic data recorded by the mine-wide network.