title of the thesis - Department of Geology - Queen's University
title of the thesis - Department of Geology - Queen's University
title of the thesis - Department of Geology - Queen's University
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Table 3.3: Summary <strong>of</strong> relevant parameter mean values and standard error for each cluster as compared to<br />
background parameter values. An asterisk (*) indicates <strong>the</strong> log <strong>of</strong> <strong>the</strong> values for scaling purposes.<br />
Parameter (Mean) Cluster 1 Cluster 2 Cluster 3 7400 Level Background<br />
Moment Magnitude (M) -1.11 ± 0.01 -1.28 ± 0.02 -1.37 ± 0.03 -1.11 ± 0.01 -1.09 ± 0.00<br />
Seismic Moment* (Nm) 7.70 ± 0.02 7.37 ± 0.03 7.23 ± 0.05 7.81 ± 0.02 7.79 ± 0.01<br />
Seismic Energy*, (J) 3.38 ± 0.04 1.73 ± 0.07 1.31 ± 0.08 2.63 ± 0.03 2.51 ± 0.01<br />
Source Radius (m) 2.10 ± 0.02 2.24 ± 0.04 2.55 ± 0.07 2.64 ± 0.02 2.71 ± 0.01<br />
Asperity Radius (m) 0.60 ± 0.01 0.59 ± 0.01 0.49 ± 0.01 0.66 ± 0.01 0.71 ± 0.00<br />
Es/Ep 8.89 ± 0.20 7.52 ± 0.28 9.42 ± 0.32 8.21 ± 0.18 8.62 ± 0.07<br />
Static Stress Drop* (Pa) 6.84 ± 0.02 6.11 ± 0.03 5.86 ± 0.04 6.05 ± 0.35 6.24 ± 0.09<br />
Dynamic Stress Drop* (Pa) 7.12 ± 0.02 6.50 ± 0.02 6.49 ± 0.03 6.88 ± 0.01 6.80 ± 0.01<br />
Apparent Stress* (Pa) 6.05 ± 0.02 4.92 ± 0.04 4.64 ± 0.05 5.37 ± 0.02 5.27 ± 0.01<br />
Maximum Displacement (m) -3.56 ± 0.02 -4.21 ± 0.03 -4.30 ± 0.04 -3.79 ± 0.01 -3.84 ± 0.01<br />
Peak Velocity Parameter (m/s) -1.36 ± 0.02 -2.01 ± 0.03 -2.09 ± 0.04 -1.59 ± 0.01 -1.62 ± 0.01<br />
Peak Acceleration Parameter<br />
(m/s 2 )<br />
6.02 ± 0.02 5.40 ± 0.02 5.39 ± 0.03 5.77 ± 0.01 5.70 ± 0.01<br />
3.2.4 Seismicity and Rockmass Degradation<br />
In <strong>the</strong> mine environment, high event rates and dense event spacing suggest progressive damage <strong>of</strong><br />
<strong>the</strong> rock mass and increased seismic hazard (Vasak et al., n.d.). The occurrence and<br />
characteristics <strong>of</strong> seismic events can be used as an indication <strong>of</strong> <strong>the</strong> physical state <strong>of</strong> <strong>the</strong> rock<br />
mass. Temporal trends in seismic event parameters indicate that <strong>the</strong> rockmass passes through five<br />
phases in <strong>the</strong> degradation process (Coulson and Bawden 2008):<br />
1. Crack closure and fracture initiation<br />
2. Fracture interaction<br />
3. Fracture coalescence (yield)<br />
4. Fracture localization (peak)<br />
5. Disassociation (post peak behaviour approaching <strong>the</strong> residual rockmass strength).<br />
Observations by Coulson and Bawden (2008) in several mines in Nor<strong>the</strong>rn Ontario demonstrate<br />
that <strong>the</strong> rock mass immediately surrounding an excavation is in a state <strong>of</strong> permanent strain<br />
(disassociation) and is aseismic. The rock mass fur<strong>the</strong>r from <strong>the</strong> excavation is continually<br />
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