The most dangerous fault line in Seattle, both in terms of earthquake and tsunami risk, is the eponymous system of shallow thrust faults[0] that run through the middle of the city and historically have produced ~7.0 earthquakes.
Seattle buildings built in the last 3 decades are explicitly designed to survive extreme earthquakes. Most of the risk is in the 1970s and earlier infrastructure, quite a lot of which has been torn down to make room for the massive growth of Seattle.