The model presented here illustrates that during accretion, the state of stress and strain in the orogen canges dramatically from pre-accretion to post-accretion time. Prior to accretion, the orogen can be explained using the critical wedge model. At this stage, deformation is concentrated at the toe of the overriding plate along a basal thrust.

During the early stages of collision, the behaviour of the orogen deviates from the critical wedge model because the state of stress changes as the principle axes rotate. Deformation localizes in the middle of the overriding wedge, and in this model is manifested by thrust faulting. As the collision advances, the deformation starts to step downward and begins to affect the leading edge of the accreting terrane. This is manifested by a series of thrust faults in the terrane in this model. This state of stress does not last long before the zone of active deformation steps downward to the base of the terrane.

After the terrane accretes, the active deformation front becomes localized at the toe of the orogen and a new critical wedge develops. At this stage, the terrane itself undergoes a widely-distributed shortening without the localization of strain into faults. This region, however, cannot be explained by critical wedge theory because it is not at failure throughout.

This model broadly approximates what is seen in real accretionary orogens. The situation modelled here is broadly analagous to what happened during the accretion of Wrangellia to North America in southern British Columbia. There, much of the deformation associated with the accretion is localized in the Coast Mountain Thrust Belt with lesser deformation within Wrangellia itself. Then, after Wrangellia accreted, the active deformation zone stepped outboard and Wrangellia remained relatively undeformed.