'The safest place to be': Why the new SR-99 tunnel will withstand large earthquakes

In 1989, an earthquake 800 miles away served as a warning for Seattle.

Unsteady video shows a 1.25-section of the elevated Nimitz Expressway along Cypress Street in Oakland, California buckling and cracking on Oct. 17, 1989. The upper deck of the viaduct collapsed on itself, killing 42 motorists driving along the lower level.

One additional person was killed while driving on the Bay Bridge, which was also stacked and similarly collapsed, according to History.com.

The magnitude 6.9 Loma Prieta earthquake in northern California happened as the Oakland A's played in the World Series, which meant it was widely recorded.

"I can still close my eyes and vividly remember the terror I felt while gripping the armrest of my seat as we were jolted back and forth, the sound like a train roaring down the tracks," then-USA Today writer Jeff Gluck recalled in a 2014 column.

The images resonated with Seattle-area experts as well.

"As soon as I saw the photos, I thought about the (Alaskan Way) viaduct because they are visually quite similar to each other -- enough similarities that it immediately made me think of the viaduct and its vulnerability," Steve Kramer, a professor at the University of Washington who specializes in geotechincal earthquake engineering, said in a video released by the Washington State Department of Transportation on Monday.

RELATED: Here's how a 9.0 earthquake would affect Washington's coast

A little over a decade later, in 2001, Washington experienced a similar force as a 6.8-magnitude quake shook Nisqually, which indeed damaged the Alaskan Way Viaduct, though not as catastrophically as what was seen in California in 1989.

The viaduct was subsequently repaired and strengthened. It required two checkups each year to ensure its safety for drivers.

RELATED: A timeline of the Alaskan Way Viaduct's checkered history:

Meanwhile, a train tunnel that runs under the Alaskan Way Viaduct's north end was not damaged.

Kramer explained earthquakes generally affect things below ground much less than things above the ground.

RELATED: The most powerful earthquakes in U.S. history

"A tunnel is in the ground, and it's surrounded by the ground, so when the ground moves, the tunnel moves," he said. "It moves with the ground. The amount of deformation imposed on a tunnel is typically much lower than it is in a structure that's above ground."

So, when The Big One hits, WSDOT officials expect the new state Route 99 tunnel to be a safe place for drivers.

The safety factor was just one reason why Seattle drivers will suffer through the so-called Seattle Squeeze over the next three weeks as the viaduct closes down for the last time and crews prepare the new SR-99 tunnel to open. The closure kicks off a "Period of Maximum Constraint" as a series of major projects disrupts traffic in the city.

After things get worse, they are expected to get better -- and safer.

RELATED: As the Alaskan Way Viaduct closes, so closes a chapter of Seattle history

"The SR-99 tunnel is designed for a 9.0 earthquake," David Sowers, WSDOT deputy administrator, said in the video. "The tunnel is composed of 14,000 concrete rings. It's all bolted together and it holds together, but it also creates some flexibility."

Should a quake strike Seattle, the tunnel will be able to move and return to its original shape.

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

Which will hopefully make surviving Viadoom worthwhile.

Producer Natalie Guevara can be contacted at natalie.guevara@seattlepi.com.