The spatial distribution and episodic nature of behind-arc spreading is as yet unexplained. The present sites of rapid marginal basin opening well-developed enough to be producing unmistakable oceanic crust are the Tonga-Kermadec, Mariana, and Scotis arcs and the Andaman Sea. In relation to a hot spot reference frame the major plate lying behind the trench in all these spreading arc systems moves away from the the subduction zone (retreats). Taking into account the behind-arc spreading, almost all of the oceanic subduction zones advance in the hot spot frame, i.e., move toward the side from which the subducted slab approaches. This leads to the suggestion that marginal basin opening may be related to a component of 'trench suction' in the driving forces of plate tectonics.