Multidisciplinary monitoring of preparation and generation of earthquakes at M2 sources in South African gold mines

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Drilling > 80 holes with a total length > 2.8 km in earthquake prone areas, conducted were multi-disciplinary studies at sites (at depths > 3km or with equivalent stress) at six South African gold mines in ever-larger scale. Microfracturing associated with a magnitude (M) 2 event as well as those in highly stressed rock mass at 1.0km depth at another mine were finely delineated and seismologically analyzed in ever-greater detail. A hole intersecting an M2 hypocenter allowed the constraint of stress. A technology was introduced that allowed to measure stress at ever-larger depths or in ever-larger magnitudes, which calibrated elastic stress modelling. Pre-seismic strain change was observed for a M0 event, which was one of the other outcomes that can be obtained only from our monitoring at the closest proximity of hypocenters.