Effect of face fracturing on shear wave coda quality factor estimated from acoustic emission events

Abstract

The dependency of the quality factor derived from S wave coda (Q(subc)) on frequency is analysed in order to understand the effect of fracturing ahead of a mining stope. Micro seismic events recorded using acoustic emission sensors in a mining environment were used in the analysis. Acoustic emissions due to rock extraction were compared to those due to fault slip. The comparison is done by considering the ray paths of the two groups of events. The ray paths of the face events pass through fractured rock around the mining stope while those due to fault slip pass thought competent rock, away from active mining. Q(subc) was computed from averaging events from the two groups and normalising by the number of events. It was found that the Q (subc) dependency on frequency follows a power law. For face events, the power law is given by Q(f)=006f(sup0.99) and Q(f)=003.f(sup1.58) for fault slip events. Q(subc) derived from face events was found to be lower than that derived from fault slip events. The degree of dependency which is given by the power law exponent was found to be lower for face events. The low dependency value is interpreted as the effect of fracturing ahead of the mining stope. The degree of dependency was found to be comparable to those found for natural earthquakes. This suggests scale invariance of the power law since the results obtained from acoustic emission events are comparable to those derived from natural earthquakes.