Margin-parallel strike-slip faults commonly develop along convergent plate margins where an oceanic plate subducts obliquely beneath a continental plate. Such faults detach a "sliver" of continental crust from the leading edge of the overriding plate; fault motion then causes the sliver to move parallel to the continental margin, in the direction of the transverse component of relative plate motion. However, few slivers move as rapidly as predicted by simple analyses of the forces acting on them. This discrepancy must be due principally to the "buttress effect": resistance to displacement of the sliver arising from a space problem at its leading edge. More simply, a sliver can move only if it has somewhere to go. Buttresses can be geometrical (as when the continental margin changes trend abruptly), or they can arise from changes in the physical properties of the overriding plate or in other factors (such as subduction angle and angle of obliquity) that help determine whether sliver motion will occur. A strongly buttressed sliver will move only insofar as the buttress can be overcome. Obvious ways in which a buttress can be overcome are by thickening the crust or widening the sliver. Examples of both are known. Crustal thickening entails elevation increase; sliver motion is opposed by both gravity and friction. Widening the sliver is a more complex process that results in areas of extension and compression forming within the sliver, as well as a characteristic pattern of overlapping, curved fault segments. This latter response may be the cause of curvature in many strike-slip fault systems.