[S07-3] Hazard and risk assessment II

[S07-3-05] TIME-DEPENDENT SEISMIC HAZARD DUE TO MINING-INDUCED EARTHQUAKES IN GAUTENG, SOUTH AFRICA

^○Brian Zulu^{1, 2}, Vunganai Midzi^{1, 2}, Brassnavy Manzunzu^1,2, Raymond Durrheim² (1.Council for Geoscience, Silverton, Pretoria, South Africa, 2.School of Geosciences, University of Witwatersrand, Johannesburg, South Africa)

A time-dependent probabilistic assessment of the seismic hazard along the densely populated northern rim of the Witwatersrand Basin of the Gauteng Province, South Africa, is described. Seismicity in this region is mainly induced by deep gold mining and the flooding of worked-out mines. Seismic hazard assessment in the gold mining regions has not been incorporated in global projects such as the GSHAP, although the seismicity related to the gold mining activities accounts for about 90% of the seismicity of South Africa. Time-dependent seismic hazard estimates are given in terms of peak ground acceleration and 5% damped response spectra at periods, 0.1 s, 0.5, 1.0 and 2.0 s for 10% probability of exceedance in 50 years (475 year return period) for two different periods named Period A (1970 - 2004) and Period B (2005 - 2015). Seismic hazard estimates are higher in Period A owing to higher activity rates than in Period B. The highest estimated PGA value was approximately 0.250 g for a return period of 475 years in the western part of the region in Period A while the corresponding estimated PGA value was 0.206 g for a return period of 475 years in the same region in Period B. The spectral acceleration values also decreased from Period A to Period B. It was observed that the Far West Rand seismic zone contributes more hazard in the study region, followed by the West Rand seismic zone and then the East Rand seismic zone. The Central Rand seismic zone is the least active seismic zone and contributes least to the hazard of the study region. The hazard estimates are higher in the western parts of Johannesburg than in the eastern parts of Johannesburg.