Mechanical models of thrust sheet motion employ a variety of assumptions about fault zone strength and rheology. However, there are few observations available to constrain the choices of fault zone rheology. This research is designed to determine the character and mechanics of shale deformation in thrust fault zones and a way to better understand how thrust sheets move. A combined field, experimental and theoretical approach will be applied to two exposures of the Lewis thrust fault in northwestern Montana and adjacent Alberta. Correlation of naturally and experimentally deformed shale fabrics in combination with theory will be used to explain the typical nonlinear rheology in shale and associated intensity and heterogeneity of deformation at the bases of thrust sheets.
