SR 99 tunnel ‘safest place to be’ during earthquake

SEATTLE -- The double-deck Alaskan Way Viaduct spells disaster in the event of a massive earthquake in Seattle.

It's a warning that played out in real life in Oakland, Calif., 30 years ago. The Cyprus Street Viaduct Collapse killed 42 people during the Loma Prieta Earthquake.

The stark similarities between that and our own viaduct in Seattle had experts sounding the alarm back then. Then in 2001, the Nisqually Earthquake hit at a 6.8 magnitude.

"In 2001, during the Nisqually quake, the Alaskan Way Viaduct was damaged on the north end of the Alaskan Way Viaduct," said tunnel expert Red Robinson. "The viaduct goes over the Great Northern railroad tunnel. The adjacent, almost underlying, Great Northern Tunnel that was built in 1905 suffered virtually no damage at all."

Tunnels, it turns out, are safer than the surface during an earthquake.

"A tunnel is in the ground and it's surrounded by the ground, so when the ground moves the tunnel moves," explained Steve Kramer from University of Washington. "It moves with the ground, so the amount of deformation that's imposed on a tunnel is going to be typically much lower than it is in a structure that's above ground."

The Washington State Department of Transportation says earthquake vulnerability was the primary drive behind replacing the viaduct with a new, modern tunnel.

Fourteen hundred concrete and steel rings make up the new SR 99 stretch, bolted together with the flexible ability to move with the ground in the event of a 9.0 magnitude earthquake.

"The SR 99 tunnel will be the safest place to be in Seattle during and after a big earthquake," WSDOT Deputy Administrator David Sowers said.

Meanwhile, one of the least safe places to be during an earthquake is open to drivers through Friday before closing for good.

 

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