title of the thesis - Department of Geology - Queen's University

The increase in event parameter values as compared to background values is associated with the
state of the rock mass. It is assumed that the rock mass in the vicinity of Cluster 1 prior to mining
of the 461 Orebody was in an intact state and is now subject to stress loading. Induced stresses
from the onset of mining in the 461 Orebody (Fig. 2.4A, B) stimulated fracture nucleation, growth
and rupture. Seismicity in this zone represents an active transition from an intact rock mass to a
damaged rock mass. Since this rock mass is remote to the main excavation, it has not been
exposed to the prolonged induced stress of the excavation and thus has not yet degraded to the
state of the rock mass hosting clusters 2 and 3. This area continues to be a source of macroseismic
events.
3.3 Focal Mechanisms
Recorded waveforms from mining-induced events can be utilized to characterize the failure mode
at the source, known as the focal mechanism. Simple shear events can be characterized using
fault plane solutions and more complex events can be described by the moment tensor.
Information gathered from these methods can then be used to estimate the stress tensor.
3.3.1 Fault Plane Solutions
Fault plane solutions are a graphical representation of a fault-slip event and integrate geological
knowledge and seismic signals. Solutions are dependent on the polarity of P-wave first arrivals
that are recorded at a number of stations. The focal mechanism can be represented on a stereonet
(Fig. 3.10) by plotting first arrival polarities and fitting nodal planes to define compressional and
dilatational quadrants. If the fault plane is unknown, the fault plane solution is ambiguous as two
solution planes exist. Pressure axes (P-axes) are oriented in the direction of maximum
compression, tension axes (T-axes) are orientated in the direction of maximum tension and null
axes (B-axes) are oriented along the intersection of the nodal planes. P- and T-axes plot in the
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