I don't think a tsunami is going to flatten the city. A wave has a lot to go through (peninsulas, narrow straights, etc) before it could reach the city, all of which would likely lessen its impact significantly. Where the area will get hit hard, though, is liquifaction and landslides.
There will be significant damage from water all around inland Puget Sound, though I agree not on the scale of the full-blown tsunami on the coast. Everything is going to shift 30 to 100 feet west over the course of a couple minutes - the water in Puget Sound is going to slosh around like crazy.
Large parts of downtown and the area between Queen Anne and Capitol Hill ( where the Amazon campus is ) are built on fill, and are likely to be subjected to liquefaction in a major seismic event. It's entirely possible that whole sections of Capitol Hill could slide into downtown too.
The hills shake and the mountains dance, and then comes the tsunami; this sounds much more exciting to read about than live through.
Yeah, and the Elliot Bay tsunami hazard map[1] is a nice reminder that most of Seattle is up some steep hills (including flat areas like SLU). The hazard map models a 7.3 earthquake on the Seattle fault, which is tiny compared to a 9.0 in the subduction zone, but also doesn't have to travel through all those narrows straits and turns.
