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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Microseismic events <strong>of</strong> this subset have an average location error <strong>of</strong> 18 feet. Events were<br />
recorded on average by 22 sensors (15 uniaxial and 6 triaxial sensors triggered on average) with<br />
<strong>the</strong> minimum condition <strong>of</strong> 8 sensors needed for an event to be recorded. Complete population<br />
statistics, including those for magnitude events and events identified as blasts can be found in<br />
Appendix B. These parameters are automatically calculated by <strong>the</strong> mine using ESG s<strong>of</strong>tware, and<br />
first arrivals for microseismic events are usually automated. Statistics for macroseismic events<br />
that are derived from <strong>the</strong> underground array may not reflect <strong>the</strong> true magnitude <strong>of</strong> <strong>the</strong> parameters<br />
because <strong>of</strong> waveform clipping for stronger events.<br />
3.2.1.1 Moment Magnitude (M)<br />
Three magnitude estimates are made for microseismic events: uniaxial magnitude, as determined<br />
from uniaxial sensors, triaxial magnitude and moment magnitude. Magnitudes in this <strong>the</strong>sis for<br />
microseismic events make reference to <strong>the</strong> moment magnitudes.<br />
Detected microseismic events within <strong>the</strong> study area range in magnitude from M = -2.3 to M = 0.8<br />
with a mean <strong>of</strong> M = - 1.09. The distribution <strong>of</strong> magnitudes peaks at M = -1.3 (Fig. 3.2). Below<br />
this magnitude a higher proportion <strong>of</strong> events is expected but events are not recorded due to <strong>the</strong><br />
detection threshold <strong>of</strong> <strong>the</strong> sensors and <strong>the</strong> minimum sensor requirement for recording events. The<br />
magnitude range can also be examined with <strong>the</strong> frequency-magnitude relation (Fig. 3.3). The<br />
shallow slope at low magnitudes demonstrates that events below M = -1.3 are infrequently<br />
recorded, though <strong>the</strong>se are expected to occur. Beyond M = 0.4 <strong>the</strong> relation breaks down due to <strong>the</strong><br />
relative infrequency <strong>of</strong> larger events as well as <strong>the</strong> recording limitations <strong>of</strong> <strong>the</strong> sensors. At high<br />
magnitudes, sensors become saturated and recorded waveforms clipped. The effective range <strong>of</strong><br />
microseismic coverage is <strong>the</strong>refore between M = -1.3 and M = 0.4. Spatially, high-magnitude<br />
microseismic events do not show preferential clustering except near blast sites.<br />
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