Typically, the time-dependent b-value has been shown to decrease prior to the occurrence of a higher-magnitude event, thus providing a possible indicator of the timing of a significant event. The Energy Index relates seismic energy to seismic moment and an increase in the Energy Index has been associated with an increase in rock mass stress levels. The distribution of P-wave velocity also indicates rock mass stress levels and is provided from time-lapse passive seismic tomography. Finally, prior studies have correlated an increased production rate (blast rate) to higher stress concentrations, potentially triggering a seismic event. Therefore, Energy Index, P-wave velocity, and blast rate may be correlated to stress levels within the rock mass and may imply the magnitude and timing of an event. In this case study, these parameters are used in a back analysis to define a safety protocol for a deep, narrow-vein, underground mine. A catalog of b-value, Energy Index, P-wave velocity, and mine excavation blasting rate, was developed and integrated as a concept of hazardous thresholds. The combination of these various parameters can be helpful in determining the potential for high-risk times and locations due to induced stress.

1. INTRODUCTION

Unexpected seismicity in deep underground mines can result in unsafe working conditions and can negatively impact production at a mine. For this reason, microseismic monitoring has been used for more than half a century to monitor induced seismicity related to stress redistribution associated with mining excavation (Mendecki, 1996). Many hundreds of microseismic events can be recorded and analyzed with high precision of measurements of location and time of the event occurrence (Urbancic and Trifu, 2000). The modern real-time seismic monitoring is used in mines to monitor the changes in microseismicity in order to predict potential instabilities (Mendecki, 1996). Seismic parameters such as b-value, Energy Index and seismic velocity calculated from real-time seismic monitoring can be helpful in understanding the rock mass behavior in order to define meaningful trends leading to the occurrence of a major shock (Swanson et al., 2016).

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