A down-to-the-east crustal tilt rate across western Washington disclosed by precise leveling over a 70-year period suggests that the Juan de Fuca plate is aseismically underthrusting the North American plate. According to this hypothesis, the frequent occurrence of large thrust earthquake that ordinarily accompany plate convergence need not be expected along the Juan de Fuca subduction zone. This conclusion is consistent with the fact that there have been no great earthquakes in western Washington in historical time (the past 140 years).