Microscopic Feather Fractures
Certain microfractures adjacent to faults in experimentally deformed cylinders of Westerly Granite form as a result of shear displacement along the primary fault, and they are oriented consistently relative to the fault surface. These fractures are described in detail because they are: (a) symptomatic of a homogeneous state of stress in the region of the fault at the time of faulting; (b) criteria to demonstrate that shear displacement has occurred along a fault; and (c) criteria to establish unequivocally the sense of shear.