"You couldn't walk," Daryl Stevens said, describing when the quake hit. "It was like a rolling ship in the ocean."
A major highway buckled in places northwest of Olympia, and another road nearby was closed by a mudslide.
The Seattle-Tacoma International Airport was closed for more than three hours, stranding thousands of people.
The Federal Aviation Administration at one point halted all flights in and out of the Northwest's biggest city and crews were building a temporary control tower because the main building was damaged too severely to use.
The air traffic center for Washington and Oregon, near Auburn, Washington, was operating on backup power. Puget Sound Energy said 200,000 customers in western Washington lost service, but power was expected to be restored by nightfall.
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