Abstract

BRANDT, M.B.C.. Weibull failure analysis of seismic event return periods in the Far West Rand and Klerksdorp-Orkney-Stilfontein-Hartebeesfontein gold mine areas. J. S. Afr. Inst. Min. Metall. [online]. 2019, vol.119, n.12, pp.995-1003. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/765/2020.

Weibull failure analyses of seismic event return periods in the Far West Rand (FWR) and Klerksdorp-Orkney-Stilfontein-Hartebeesfontein (KOSH) gold mine areas were completed for the period October 2012 to January 2018. The analyses reveal that seismic event occurrences in the gold mines mostly follow a Poisson process for magnitudes M > 2. This implies that the event catalogue for a classical hazard analysis does not require declustering, provided mining activities and the time-of-day pattern are constant throughout the period. The Weibull analyses were benchmarked against event occurrences in the southern California earthquake catalogue. Two failure systems for small and larger events with short and longer return periods, respectively, were identified. An excessive number of dependent events with short return periods were interpreted as fore- and aftershocks. The FWR and KOSH sub-catalogues reveal comparable, but also different, event occurrences to those for southern California. Very few dependent events could be recognized for short return periods, rather than the excessive number of events expected when assuming a Poisson process. Two failure systems were identified for lower-magnitude events with longer return periods. For KOSH, the two failure systems were found to overlap at lower magnitudes than for FWR.

Keywords : Weibull analysis; mining-related seismic event; return period.

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