In 2014, a M5.5 earthquake ruptured the range of depths between 3.5 km and 7 km near Orkney, South Africa. The main and aftershocks were very well monitored in the nearfield by dense, surface, strong motion meters and a dense underground seismic network in the deep gold mines. The mechanism of this M5.5 earthquake was left-lateral strike-slip faulting, differing from typical mining-induced earthquakes with normalfaulting mechanisms on the mining horizons shallower than 3.5 km depth. To understand why such an unusual event took place, the aftershock zone was probed by full-core NQ drilling during 2017-2018, with a total length of about 1.6 km, followed by in-hole geophysical logging, core logging, core testing, and monitoring in the drilled holes. These holes also presented a rare opportunity to investigate deep life. In addition, seismogenic zones of M2-M3 earthquakes were probed on mine horizons that were also very well monitored by acoustic emission networks. This paper reviews the early results of the project.

Kanowna Belle went underground from the open pit in 1996. At the start of 2000 the decline had reached 950 m below surface and stoping was down to 740 m. Seismicity was starting to occur and by May 2000 a seismic system had been commissioned. Since then, seismicity has played an increasing role in risk management of the mine, both in respect to safety and production. Seismic events with increased damage potential only started to occur mainly below 970 m depth (below C-block). The increase in seismic risk has lead to the development and implementation of the Garford yielding bolt, the development of seismic management systems and the adaptation of the mining method and sequencing. With increasing depth and seismicity, development of the lower E-block the mine is now moving into a new environment where new support systems and seismic control systems are being developed and implemented. This paper highlights the need for long term planning strategies, good quality seismic and geology data collection, analysis and recognition of high risk zones and subsequent management systems that involve planning, analysis, support, exclusion zones and education/communication of the work force.

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The Ernest Henry mine (EHM) in Queensland, Australia is developed to a depth of just over 1 km, and current active production cave levels have reached a depth of 730 m. Caving started just below the pit floor at a depth of 535 m, and is progressing deeper. The impact of stress and seismicity with increasing depth requires ongoing review and re-assessment of established practices and standards, and the implementation of new measures where required. Adverse effects of stress and the associated seismicity can have a significant impact on the safety, production and morale at a mine site. At EHM, an inclined sublevel caving operation, the geometry of the orebody and increasing depth provides for some interesting stress and seismic impacts, which are actively monitored and assessed. This paper outlines some of the observed rock mass responses, the impacts these had, and ongoing measures implemented to provide stability in an increasingly challenging environment.