[S02-5] New directions in anthropogenic seismicity studies I

[S02-5-03] The Spatio-Temporal Variation of Seismicity in the South African Gold Mining Region

^○Vunganai Midzi^{1, 2}, Brian Zulu^{1, 2}, Denver Birch¹, Andrzej Kijko³, Ansie Smit³ (1.Council for Geoscience, Pretoria, South Africa, 2.University of the Witwatersrand, Johannesburg, South Africa, 3.University of Pretoria, Pretoria, South Africa)

The creation of a reliable earthquake catalogue with homogenous magnitude representation (Mw) is an essential step for the development of a probabilistic seismic hazard model. In preparing to conduct a seismic hazard of the Gauteng province in South Africa, such a catalogue of seismic events was compiled by combining publicly available earthquake information from the Council for Geoscience datasets. Two main datasets used in the creation of the catalogue are from the South African National Seismograph Network and the Gold Mines cluster networks. The SANSN catalogue consists of 49812 records of earthquakes occurring between May 1905 and December 2014, whilst the Cluster network catalogue has 7828 records between March 2010 and December 2014. Results of preliminary analysis of the data show a strong spatial and temporal variation in the occurrence of seismicity in the region. The seismicity characteristics of an area are usually described through the seismic hazard recurrence parameters, the mean seismic activity rate, λ, the Gutenberg-Richter b-value and the area-characteristic completeness magnitude, Mc. These parameters were investigated in terms of their temporal variation within the various mining regions of the Witwatersrand basin, using the ZMAP software package. The region was divided into four sub-regions, Klerksdorp-Orkney-Stilfontein-Hartbeesfontein (KOSH), West Rand, Central Rand and East Rand. In some regions mining stopped some years ago, yet seismicity continues to occur. Researchers linked this seismicity to flooding of the mines. Results of the analysis showed a strong influence of the temporal distribution of seismograph stations on the observed variation of recurrence parameters. However, physical processes such as the flooding of mines as well as the occurrence of large events also influenced the occurrence of events. A recommendation from this investigation was that time dependent seismic hazard assessment should be conducted for this region.