The Nature and Possible Source Mechanisms of Seismic Events From a Shallow Pillar Supported, Platinum Mine in South Africa

ABSTRACT: Seismic data recorded by near surface geophones over a period of 20 months at a 900 m deep platinum mine in the Bushveld Igneous Complex (BIC) have been analysed. The mine is supported by a system of reef pillars and the objective of the analysis was to distinguish between pillar failure related seismicity and that caused by shearing on geological discontinuities. An area of relatively high seismic activity was highlighted for study. The evaluation of several parameters, which, together can be considered to indicate seismic risk, correlated well with the increased seismic activity. A newly developed data analysis technique was applied to investigate source mechanisms. Three possible mechanisms which fit the data were postulated. Two of these have been observed underground, the most common being pillar punching.