Evaluation of the seismic rock mass response to mining and the impact of preconditioning using an epidemic-type aftershock model

Abstract

Preconditioning techniques are frequently used to reduce the seismic hazard induced by mining under high-stress conditions. However, the impact of preconditioning on the seismic rock mass response has not been completely quantified. This study evaluates the impact of preconditioning using an Epidemic-Type Aftershock Sequence (ETAS) model. This stochastic model simulates a process in which each event produces its own offspring events. For the analysis, the mining-induced seismicity recorded during the construction of the New Mine Level Project (NML) tunnels at the El Teniente mine was used. The data was divided into five scenarios depending on the type of preconditioning applied. Next, the parameters of the ETAS model are estimated for each scenario and compared. The results show that both hydraulic fracturing (HF) and destress blasting (DB) increase the speed of decay of seismicity after blasts. However, only HF has a significant effect on reducing the seismic hazard and the background levels of seismicity. The α parameter of the ETAS model, which measures the efficiency of a given magnitude in producing its offspring, is proposed to quantify and classify the seismic hazard amongst the NML tunnels. Additionally, a residual analysis based on the difference between the recorded seismicity and that estimated by the ETAS model is proposed to evaluate the seismic rock mass response to mining in calibration and application. Auxiliary graphs to better understand the fluctuations of the residuals are also provided.