Can you draw the upper shear zone margin on Figure 15.9? Is it easily definable?
What will be an ideal response?
Ans: The upper margin is, by definition, located at the transition from unstrained to (weakly) strained amygdales. This is quite difficult to identify because the initial amygdales are irregular and with slightly different shapes. It may perhaps seem like there is a weak preferred orientation of amygdales outside the shear zone boundary as drawn in Figure Q15.2. It is difficult to know if this is a weak but pervasive strain on which the shear strain was superimposed or if it is related to the shear zone.
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