From SDOT:

Responding to this morning’s earthquake, the Seattle Department of Transportation (SDOT) is inspecting the city’s elevated roadway structures for any possible damage. The department has already examined the Ballard, Fremont, University and Spokane Street bridges and has found no indications of damage from the earthquake. The inspections will continue with assessments of the Magnolia, Emerson Street and Jose Rizal bridges, the 15th Avenue NW Interchange and the Spokane Street Viaduct.

Given the small size of the earthquake, the department is carefully examining a key number of its bridges, viaducts and overpasses. If any earthquake damage is discovered, SDOT will then escalate its inspection to all citywide elevated roadway structures.

The Washington State Department of Transportation is responsible for inspecting the Alaskan Way Viaduct and is already at work on that important elevated structure.

ADDED 12:16 PM: SDOT has sent an update:

Inspections of elevated roadway structures across the city
by the Seattle Department of Transportation (SDOT) revealed no damage
from this morning’s earthquake. … In addition to visual inspections, SDOT performed test openings on the four movable bridges and found all systems operating correctly. This testing covered the Ballard, Fremont, University and Spokane Street bridges.