The islands in Puget sound show a history of vertical motion +-50 ft. or more.
The subduction area is offshore a pretty good distance. A tsunami from there would have trouble getting into Puget Sound.
The problem is there are assorted other faults on shore, one directly under Seattle. A 7.0 quake on that would be worse for Seattle than a 9.0 on the Subduction zone. 1,100 years ago a quake on the Seattle Fault caused a tsunami on the site of present day Seattle.