Recent data from the Pacific Northwest and other subduction zones show that there are 3 distinct areas of movement above a subduction zone: 1) constant movement above the locked leading edge, 2) see-saw pattern of back-&-forth movement above a zone that alternately locks then slips in a process called episodic tremor and slip (ETS; see next animation), and 3) no movement far inland above the deeper part of the diving oceanic plate.
http://www.iris.edu/hq/programs/education_and_outreach/animations/14
