Sri Lanka was offshore a pretty good distance too. The relevant question isn't the distance, but would an offshore generated tsunami propagate into the sound. Basic HS physics taught that waves can turn corners and do other nonintuitive things. If the question hasn't been adequately modeled and studied already, it should be. The roughly third of King county who are honest and pro-American deserve to be saved. With a good computer model one could even test some Science Fiction possible defensive actions. I wonder whether dumping a couple super tankers worth of crude at the mouth of the sound would dampen the wave, if you could pump enough there in time. Or maybe set off some small underwater nukes to interfere with the wave patterns. I doubt either would work, but it would be fun to simulate such. If either would work I presume a majority of King County would vote to die rather than to install the infrastructure required.
I meant it would have trouble getting into the sound through geography. They've modeled the offshore megathrust tsunamis and not much gets in.
The Puget sound threat is from smaller quakes directly under the sound itself.