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

Figure 3.20: Distribution of double-couple event mechanism types on the 7400 Level.
In conducting fault plane solution analysis, a number of events were discarded that did not have
adequate statistical or visual fits. Failure to fit a double-couple solution can be a result of either
(or both) the fault plane solution method or the physical failure process. Poor solution fits can be
a result of poor focal sphere coverage, poor first arrival picks, uncertainty in first arrival polarities
or insufficient polarity information (Urbancic and Young, 1995).
Poor solution fits can also be obtained if the solutions do not have a double-couple solution. Nondouble-couple
solutions are a result of the physical failure process and occur when the moment
tensor contains components other than pure shear, such as volume change. Blasts, for example,
cause large volumetric changes and result in non-double-couple mechanisms. Deviations from the
double-couple solution are expected in the mining environment since a number of free surfaces
exist along which fractures can interact during failure. Intersections of fractures and openings,
complex interactions between fractures as well as closely spaced failures in time and space are
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