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

quadrants of dilatation and compression, respectively) and are oriented orthogonal to each other
and 45° to the nodal planes (Fig. 3.11; Stein and Wysession, 2003. P- and T-axes approximate
maximum principal stresses, though these can differ significantly if failure occurs along preexisting
structure (Gephart and Forsyth, 1984).
Figure 3.10: Block model of a shear-slip event and corresponding focal mechanism and waveforms,
modified from Stein and Wysession, (2003).
Solutions are limited to pure shear event mechanisms only, that is, mechanisms with doublecouple
sources. Double couple (DC) sources have source radiation patterns that can be described
by coupled forces with no net torque (Fig. 3.11; Stein and Wysession, 2003).
Figure 3.11: (Left) coupled forces along fault and auxiliary planes; (middle) paired force couples (doublecouple);
(right) resultant fault plane solution, where shaded quadrants are in compression. Modified from
Stein and Wysession, (2003).
Events involving interaction between more than one fracture, volume change and those having
mixed mechanisms cannot be represented using the fault plane solution method (Miller et al.,
1998; Stein and Wysession, 2003). Voids created by mining often cause extension and thus non-
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