By JCP Geologists

Magnitude 6.8 Earthquake Strikes Seattle Area

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Seattle, WA -- A magnitude 6.8 earthquake occurred at 10:55 a.m. PST approximately 30 miles south of Seattle, Washington near the City of Olympia. The earthquake's epicenter is near the location of the magnitude 7.1 earthquake that occurred in 1949.

Although the earthquake was large in magnitude, it was quite deep at approximately 50 kilometers. As a result, ground shaking was weak throughout most of the region, and damage patterns seem to match this. The epicenter was located about 10 miles north east of Olympia.

In Seattle, no modern engineered buildings displayed any significant damage. Scattered damage of unreinforced masonry buildings (URM) was noted in the Pioneer Square area. Roughly 1 in 10 URM buildings suffered significant damage including parapet failures, parapets leading to peeling off of the tops of walls, and blow out type out-of-plane wall failures. In the Duwamish area, moderate damage was noted in low-rise industrial buildings of various types.

Water systems in the area faired very well with only 20 main breaks. Electric power also faired very well, with some rather minor substation damage. Power was lost to about 200,000 customers and was restored within hours. There were a few fires, but nothing of particular note and since water pressure was maintained, these were easily extinguished.

Bridges in the area also faired very well. The Alaska Viaduct running along the West side of Seattle was closed for two days, but suffered no apparent damage of significance.

SEATAC airport suffered extensive damage to the control tower. The Tower was permanently closed, resulting in about an 8-hour closure for the airport while the FAA mobilized a portable military control center. This allowed operations to resume to a 50% level. Additional mobile tower equipment will be provided to enable full operation while a new tower is built. Runways at the King County Airport (Boeing Field) were disrupted by moderate liquefaction and the facility also suffered damage to the tower and some hangar buildings.

Moderate liquefaction was reported throughout the region, including the Port of Olympia and the Port of Seattle. Liquefaction was accompanied by sand boils, sink holes and modest lateral spreading, with 1 to 1-1/2-inch cracks paralleling the waterfront for 300 to 400 feet at a stretch. There was no impact to the cargo cranes as they are on piled rails. The ferry terminal suffered a large crack across its elevated deck and has been closed for inspection and repair.