Characterization of Aseismic Fault-Slip in a Deep Hard Rock Mine Through Numerical Modelling: Case Study

Seismic moment is a predominantly utilized parameter for assessing fault-slip potential when the numerical modelling of fault-slip is carried out. However, relying on seismic moment as an indicator for fault-slip might lead to incorrect conclusions, as fault-slip can be inherently seismic or aseismic. The present study examines the behaviour of a fault in Copper Cliff Mine, Canada, with a 3D numerical model encompassing major geological structures in the area of interest. Three types of numerical analyses are conducted, namely elastic and elasto-plastic analyses in static conditions and elasto-plastic analysis in dynamic conditions. The static analyses show that the fault most likely had undergone shear failure at the pre-mining stage. It is then demonstrated that mining activities induce further shear movements along the fault plane as well as within the fault material, as the fault is composed of thick, severely fractured materials. Notwithstanding the results, no large seismic events with M_w > 0.1 were recorded within the fault from microseismic-monitoring systems between 2006 and 2014, implying that the shear movements are aseismic and static. Furthermore, microseismic database analysis using 350,000 events that took place between 2004 and 2014 indicates that the fault is not seismically active. It is found from the dynamic analysis that the maximum slip rate during fault-slip is not more than 0.3 m/s, even when the fault-slip is simulated with an instantaneous stress drop. This result substantiates the assumption that the fault is not seismically active and shear movements are dominantly aseismic. It is therefore suggested that other factors such as stress re-distribution induced by the aseismic slip be considered in order to assess damage that could be caused by the fault movements. The present study sheds light on the importance of distinguishing aseismic from seismic fault-slip for optimizing support systems in underground mines.