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

3.2.1.3 Energy Ratio, E s /E p
The ratio of S-wave to P-wave energy (E s /E p ) is commonly used to identify source mechanisms.
Events with high E s /E p ratios are most likely caused by shear failure along a geological structure
while lower ratios may have a complex or dilational component of failure (Gibowicz and Kijko,
1994). While traditionally the cutoff for E s /E p is 10 (Gibowicz et. al, 1991) for discriminating
between extensional blast events (E s /E p 10), this value is too
large to discriminate between shear and extensional microseismic events. A cut-off of E s /E p = 5 is
deemed appropriate for Creighton Mine because the mean E s /E p of microseismic events is 8.6, for
macroseismic events is 16.3, and for blasts is 6.2 (Fig. 3.5). Previous work in Creighton Mine by
Vasak (n.d.) also deems an E s /E p ratio of 5 to be appropriate for Creighton Mine. Microseismic
events having high E s /E p are randomly distributed, rather than being located along large
discontinuities as would be expected from fault slip. No spatial trends were identified for events
between the 7200 and 7530 Levels and thus no correlations between E s /E p and geological structure
are made. Spatial distributions of detected E s/ E p events can be found in Appendix B.
Frequency (% of total)
35
30
25
20
15
10
5
2006 Blast and Event Distribution (% of Total)
Blasts
Events
0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Es/Ep
Figure 3.5: Es/Ep ratios measured for 2006 events and blasts. The cut-off of 5 is shown by the dashed line.
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