Abstract Fold and thrust belts are contractional systems created by tectonic plate collisions, creating stress conditions where the maximum principal stress is horizontal and the minimum principal stress is vertical. The stress orientation favours the development of low-angle reverse faults. The trigger mechanism for thrust activation as a recurring seismic event is related to fluctuations in fluid pressure. The fluctuating fluid pressure creates a temporal cycle of elevated and relaxed fluid pressure that shifts the system in and out of failure conditions. The generation of hydrocarbons from organic material is a source of fluids and a means of temporally fluctuating the fluid pressure. In the southern Canadian Rocky Mountains the major detachments follow organic-rich strata that have generated hydrocarbons. The nature of the fluids impacts the size and distributions of faults within the tectonic wedge. The critical taper of the wedge is modified by the presence of high fluid pressure.