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

3.2.1.4 Stress Parameters
Stress parameters quantified from event spectra (Mendecki, 1997) include static stress drop,
dynamic stress drop and apparent stress. Static stress drop,
, is defined as the average
difference between the initial and final stress levels over a fault plane (Gibowicz and Kijko,
1994). Dynamic stress drop,
d
, is the effective stress representing the difference between the
initial stress and the kinetic friction level on a fault (Gibowicz and Kijko, 1994). The apparent
stress, is proportional to both the seismic energy and the seismic moment:
a
, (Equation 3.1)
where μ is the shear modulus of the source medium, E is the seismic energy and M o is the seismic
moment. The distribution of event stress parameters displays similar spatial trends as energy and
seismic moment with low parameter magnitudes to the south and south east of the excavation,
higher parameter magnitudes to the southwest of the excavation, and elevated values where
mining took place in the easternmost stopes during the time span under analysis (Appendix B).
3.2.1.5 Source Dimensions
Calculated source dimensions include source radius, r o , and asperity radius r a . These values are
derived from spectral parameters and based on a dynamic circular fault model (Madariaga, 1976).
Such calculations are thus highly dependent on modeled spectra (Gibowicz and Kijko, 1994).
Large source radii occur to the west of the excavation. Clustered events to the southwest of the
excavation have small source radii while low to intermediate values exist to the south and
southeast of the excavation. Asperity radii are largest to the east of the excavation and more
variable south of the excavation away from blasting.
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