A thrust duplex is a system of imbricate thrust faults that branch off from a floor thrust below and curve upward to join a roof thrust at a branch line above, thereby forming a stack of horses (Figure 6.14; compare Figure 4.26 A). Unlike an imbricate fan that can break through to the surface, a duplex is necessarily contained within the stratigraphic section. Like an imbricate fan, however, a duplex can develop along a frontal ramp on which the main thrust rises toward the foreland.