Seismic damage mechanism at Impala Platinum mine

Ledwaba, Lesiba Shalkie
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Impala Platinum Mine (Impala), situated north of the town of Rustenburg in the North West Province of South Africa, has experienced an increase in seismicity from ~841 seismic events in the year 2005 to ~1588 seismic events in 2008. The seismologists and rock engineers need to understand the underlying mechanisms and driving forces responsible for seismicity to develop and design mining layouts and support strategies to lessen the risks posed by rockburts. However, most previous studies of seismicity conducted on Impala and other Bushveld Complex mines in the Rustenburg area provided limited information regarding the source parameters and mechanism due to insufficient data. The study is designed to investigate the seismic hazard on Impala Platinum Mine by means of two approaches: an investigation of seismic source parameters and the mechanism of potentially damaging seismic events, and mapping of the weathered layer of the near surface within the Impala mine lease area. A number of detailed investigations of rockbursts were conducted whereby damage was mapped and photographed. The investigations includes reviews of the seismic history, short-, medium- and long-term seismic hazard assessment methods, and an analysis of the source parameters of the seismic event and associated ground motions. The study has revealed that most of the seismic events occur close to the reef plane, and are the result of the failure of a volume of rock that includes the pillar and the host rock that forms the foundation of the pillar.
A dissertation submitted to the Geophysics Department, School of Geosciences, Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Masters of Science. Johannesburg, February 2012