P/S amplitude ratios for mining related events in South Africa: Implications for low-yield explosion monitoring

Abstract:

Seismic detection and discrimination of tectonic, and anthropogenic seismic sources are essential for seismic monitoring and enforcement of nuclear test-ban treaties. Among many analytical methods, the P/S amplitude ratios are widely used for seismic source discrimination at teleseismic and regional distances. However, distinguishing low yield seismic sources at local distances (< 200 km) are partially investigated due to lack of local to near-regional data coverage. In this study, we analyze the observations from 170 mining related events (rock bursts, slip burst and pure slips extending to depth of 4.25 km) observed at distances less than 120 km, within and adjacent to the Kloof gold mining region of South Africa. Event magnitudes range from 0 to 3.1, but include no known explosions, so our focus is on the comparison of P/S ratios for different mining-related events. Local ground motions were recorded using 67 surface accelerometers operating in 2012-2017 around the Kloof Gold Mine. After correcting instrument effects, we visually pick all P- and S-wave arrival times and measure the P and S wave amplitudes across several frequency bands in frequency domain. Before determining the P/S ratio, we apply a magnitude and distance amplitude correction (MDAC) to the measured P and S amplitudes. We analyze, quantify, and compare the patterns of MDAC-corrected ratios for rock bursts, slip burst and pure slips events in Kloof mine and explore for distinguishable patterns. Our preliminary results revel two distinct patterns of P/S ratios among pure-slip and rock burst for some seismic events, but the patterns are complex for other events. The results from this study will help to enhance our understanding of low-yield seismic events discrimination which is important in seismic monitoring.