Last Friday’s 4.5 magnitude earthquake was not-so-gentle reminder of just how much Gov. Chris Gregoire, Seattle Mayor Greg Nickels and (soon to be former) King County Executive Ron Sims are gambling in their deliberations and recommendation for replacing the Alaskan Way Viaduct.

It was the imminent threat of earthquake that boosted the $4.24 billion viaduct project on Seattle’s downtown waterfront and, to a lesser extent, the $4.5 billion Highway 520 bridge project, to the top of the state’s priority list for money. Those two projects were the main reason the Legislature approved raising the gas tax by 9.5 cents a gallon in 2005.

State highway engineers say there is a 10 percent chance that over the next 10 years, there will be an earthquake severe enough to make parts of the viaduct collapse.

Ron Paananen, DOT deputy urban corridors director and the guy who oversees the viaduct replacement project, said earlier this week that translates into a 1 percent chance each year that the viaduct may crumble. Conversely, that means there’s a 99 percent chance that it won’t.

Gregoire, Nickels and Sims were playing the odds over the past two years while they were negotiating a deal. They still are.

The governor issued an ultimatum a couple years ago, saying the viaduct was coming down no later than 2012, so all interested parties had better come to an agreement.

Now, the trio are recommending to the Legislature that the viaduct stay in place -- it carries 110,000 vehicles a day -- until 2015, while a deep-bore tunnel is dug about 300 feet from seawall.

That means the trio are still playing the odds.

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They’re gambling that the viaduct will still be upright 14 years after the Nisqually earthquake, the one that so startled everyone into making the viaduct the top transportation project in the state.

Odds makers will tell you the odds are the same every year. It’s 1 percent this year, 1 percent next year, and so on. The passage of time doesn't increase the odds to say, a 14 percent chance of collapse in that final year (but don't tell that to someone in Vegas who's throwing the dice.) The odds are still 1 in 100.

Nonetheless, last Friday’s earthquake got the attention of engineers about just how vulnerability the viaduct is.

“It definitely was a reminder,” Paananen said Monday. He confirmed that leaving the viaduct up during tunnel construction is “exactly the plan.

“People don’t want to live too long without Highway 99,” he said. (The viaduct is 99 through that part of the city.)

He noted the current standard for highway and bridge construction is solid enough to withstand a 1,000-year quake -- that is, build structures so soundly they can handle the kind of earthquake that rolls around only once every 1,000 years.

“Damage, but no loss of life,” Paananen said.

Apparently, Nickels, Sims and all those downtown Seattle business types who envision an unobstructed view of Elliot Bay, who want to open up Seattle’s waterfront by removing the eyesore that is the viaduct, persuaded the governor the new plan is worth the risk.

Now, it’s up to the state’s 147 legislators to decide whether they like those 100-to-1 odds.

No one is out of the woods, yet.