And they're already anticipating what a 9.0 quake, or higher, might do to Seattle.
This article runs through it in some detail, with the eventual recommendation to be prepared to live three days alone, without food or water.
From their report of a 2008 study: "In that study engineers looked at 575 buildings from the outside and further that estimated 850 to 1,000 old brick buildings that date back to the 1930s would be at risk if a 6.7-magnitude earthquake occurred on the Seattle fault, which runs through the center of Seattle and Bellevue. The Seattle fault is widely considered the most dangerous quake threat to Seattle. Scientists have predicted that a significant earthquake on this fault could cause widespread devastation and at least 1,000 deaths in the city because of collapsed buildings, fires and other infrastructure failures."