Where is the footwall flat? A cautionary note on template constraints

Sand-box models and field observations are used to illustrate limitations associated with template constraints in the analysis and interpretation of thrust systems. Model results show that, at shallow levels, shortening is taken up by displacement along thrust surfaces, whereas ductile deformation accommodates shortening at deeper levels. This variation in deformation style, which also is observed in nature, may contradict the necessity of correspondence between footwall and hanging wall ramp and flat structures. Hanging wall flats that form the base of an imbricate sheet for a relatively long distance may not have the corresponding footwall flats. Unlike the template constraint model, the model footwall flat is represented by a broad zone of ductile deformation with significantly less fault slip than along the shallower parts of the imbricate.