News

State:Earthquake wouldn't hurt tunnel

Puget Sound Business Journal - by Steve Wilhelm

Date:Monday, March 28,2011

State transportation officials have since the outset been studying the impacts of possible

eafthquakes, tunamai and climate change on the planned Seattle deep-bore tunnel and a cut

and-cover version previously proposed.

They're convinced the tunnel won't be flooded in the next century and will be able to withstand

up to a 9.0 earthquake.

"We've been thinking about this since 2004, when the first draft EIS was issued and tunnel

proposed", said Ron Paananen, the Washington Department of Transportation Alaskan Way

Viaduct and Seawall Replacement  Program administrator. "We have evaluated the possible affects

of rising sea levels and tsunamis and have concluded they do not pose a risk to the tunnel."

"The University of Washington Climate Impacts Group has in the last few weeks updated its

estimates of sea level rise in Puget Sound by 2100, and the range is substantial, from a low of 6

inches to a high of 4.2 feet", said Lara Whitely-Binder, outreach specialist  for the group.

Previous WSDOT studies had put the top end of sea level rise at 2.8 feet overt he next 75 years.

"The larger number includes eight inches of Seattle land subsidence, which would lower the land

while the water is rising due to arctic melt", Whitely-Binder said.

"Despite the higher top-end estimates for sea level rise", Paananen said, "current studies show that

the planned Seattle Seawall's eight feet of freeboard over average high tide means that the

possibility of any flooding of the south portal of the tunnel during a large earthquake is very small."

He added that deep ocean tsunamis would be largely dissipated by the time they made their way

down Puget Sound to Seattle, and earthquakes withnin Puget Sound would generate only smaller

tsunamis.

"The tunnel is being designed to withstand a very strong earthquake, and tsunamis are an even

rarer event in Seattle. It 's a very low-risk item", he said." If we look at this again and decide it is an

issue, there are ways to protect the portal against extra sea level rise."

STEVE WILHELM covers manufacturing aerospace and trade for the Puget Sound Business

Journal.  Phone: 206-876-5427/E mails: wilhelm@bizjournals.com.