Seattle 10 Years After Nisqually Quake

Ten years after a 6.8 earthquake shook the Pacific Northwest, there is still a scramble over seismic hazard preparations.

Ten years ago today, Seattle's Alaskan Way Viaduct, a two-level overpass highway along the waterfront, came dangerously close to collapsing during the 6.8 magnitude earthquake that shook northwest Washington. As long as the overpass remains standing, it is an iconic reminder that Seattle is not yet ready for the next big quake.

Demolition of the overpass began this month, but its replacement tunnel is still under contentious debate. The above Discovery News video demonstrates the potential risk facing Seattle's waterfront and shows why the overpass is considered the city's most dangerous architectural feature.

Built in 1954, the Alaskan Way Viaduct is currently in a position that could rival the famous 1940 collapse of the Tacoma Narrows Bridge.

While city planners continue to argue with the mayor over what's best and most cost efficient for improving Seattle's waterfront safety, geologists are focusing their efforts on improving the seismic knowledge of the region, including identifying previously unknown fault locations. Recently, seismologists have even begun giving serious consideration to what is usually dismissed as quackery: earthquake prediction.

Quoting seismologist John Vidale, Director of Pacific Northwest Seismic Network and a professor at the University of Washington, the university reported that:

Scientists here and around the world are trying to devise methods to predict earthquakes, "but right now we can't even see how that might work," Vidale said.

Seismically more attainable, yet financially still exorbitant, is an earthquake warning system - which might give notice of an earthquake within seconds of its occurrence. The warning would have to travel faster than the seismic waves to provide cities away from the epicenter with enough notice to take action.

From the University of Washington in Seattle again:

It also is possible now to develop an early warning system, using data from sensors close to an earthquake source to determine which direction the waves will go and how strong the shaking might be. Such systems are already being used in Japan, Mexico and elsewhere. "That could give people advance warning ranging from a few seconds to a few minutes," Vidale said. "The question is whether it is worth the financial cost."

Currently the budget for installing enough seismic sensors to initiate a warning system would cost $40 million and take five years to build.

But John Dodge of the Olympian newspaper in Washington reminds readers that:

In 2005, a team of geologists, structural engineers, seismologists and emergency management officials gathered to answer the question: What would happen if a magnitude 6.7 quake occurred on the Seattle fault today? Here's their answer: $33 billion in property damage and economic loss, more than 1,600 deaths, more than 24,000 injuries, and nearly 40,000 buildings destroyed or unfit to occupy.

Following the Kingston, Wash., 4.5-magnitude strike-slip earthquake in 2009, a similar intraplate earthquake to the Nisqually quake of 2001, the U.S. Geological Survey estimated that the "likelihood of another potentially damaging intraplate earthquake during a 50-year time window with the Puget Sound region put the probability at about 84%, with somewhat lower probabilities as one goes southward."

The soft sediment under many of the cities in the Pacific Northwest is one of the key factors making the region vulnerable to shake-induced damage. The soft ground acts to magnify the ground response to the earthquake. The recent updates to building codes take this into account. For example, the 2001 Nisqually earthquake struck during construction of the Seattle's new football stadium. The structure, which sits on pilings driven deep into bedrock is now known in good standing for it's rock-n-roll capabilities.

The tunnel poised to replace the Alaskan Way Viaduct will have to pass even stricter regulations as building codes have changed three times since 2001 to incorporate the updated seismic science. Just seeing the start of the viaduct's demolition however is reason enough to stand-up and cheer.

Image 1: U.S. Geological Survey shake map of the Feb. 28, 2001, Nisqually earthquake.

Image 2: U.S. Geological Survey 2009 seismic hazard map for Washington.