Getting ready for the Big One

The images of the quake aftermath in China raise the question: What would the wake of a major quake look like in Seattle? Fortunately, we have the answer. Or at least a pretty good guess.
Crosscut archive image.

A map of the Seattle Fault, best as geologists can render it. (U.S. Geological Survey) Click to enlarge.

The images of the quake aftermath in China raise the question: What would the wake of a major quake look like in Seattle? Fortunately, we have the answer. Or at least a pretty good guess.

Events in China have nudged earthquakes closer to the top of our minds. Here in Seattle Mayor Greg Nickels is calling for seismic retrofitting of nearly 1,000 of the city's older brick buildings, which are at risk in the event of a major quake. Seeing the devastation in southwestern China, it's hard not to wonder what could happen here. We're told, a major quake is just a matter of time. How would we fare? And what would the aftermath look like?

We've done our homework. In 2005, the Earthquake Engineering Research Institute, an Oakland, Calif., non-profit group, conducted an extensive study of what would happen if Seattle were hit with a 6.7 quake on the Seattle Fault, which runs roughly from Hood Canal to Issaquah and right through Seattle. The so-called "Seattle Scenario" [38.2 MB PDF] is chilling. The quake in China was 7.8 on the Richter scale, but the projected Seattle one is smaller, comparable to the Nisqually quake (6.8) of 2001. Unlike Nisqually, however, it would be right under our feet.

Even so, the projected losses are appalling: With $33 billion (that's on the low side) in losses, there would be 1,600 dead and 24,000 injured, and 9,700 buildings and homes would be completely destroyed, 29,000 rendered unsafe for use, and 154,000 suffering moderate damage. The quake would collapse bridges, shut down highways for weeks or months, and cause more than 1,000 landslides, some of which, in turn, could cause mini, localized tsunamis.

The Nickels plan is based on a 6.7 scenario, too. According to The Seattle Times, last year "engineers looked at 575 buildings from the outside and estimated 850 to 1,000 such buildings in the city would be at risk if a 6.7-magnitude earthquake occurred on the Seattle Fault ..." Retrofitting them all would cost $358 million to $431 million, according to the Times. Most were built in the 1930s and earlier, and they cluster in neighborhoods like Ballard, the University District, First Hill, Capitol Hill, the waterfront, Pioneer Square, and the International District. The southernmost neighborhoods would likely be the hardest hit in the Seattle Scenario because they're closer to the epicenter and because of soil conditions. (Here's a look at local earthquake hazard zones.)

But they aren't the only structures at risk. Many modern, concrete buildings, such as the boxy factories and warehouses in SoDo or retail and manufacturing sprawl zones like the Kent Valley, are also likely to topple. And, according the the scenario's numbers, even if all 1,000 Seattle brick structures were retrofitted and didn't collapse, another 8,700 building of various kinds would be destroyed, either in the quake or the aftermath (landslides, floods, fires). In other words, retrofitting is common sense, but there's no panacea, and even the mayor's proposal doesn't cover all the buildings that need retrofitting.

A 6.7 quake in Seattle would severely damage and hamper our transportation infrastructure, according to estimates. Since disasters are commonly used these days to prod people to fix the Alaskan Way Viaduct and replace the 520 bridge, it is worth noting that while building stronger roadways might be ideal, given our locale and geography, nothing we do will make us entirely earthquake-proof.

Another thing the scenario looks at is disaster recovery time: Economic losses are largely determined by how fast a damaged, modern city (Los Angeles, San Francisco, and Kobe, Japan) can get back on its feet. One of the most expensive earthquake disasters in this respect was the 1994 Northridge quake in Southern California, but the Seattle Scenario's authors point out that recovery there was quicker than what Seattle could expect because the Los Angeles freeway system has a lot of redundancy. We have comparatively few freeways, and alternative surface routes would likely be jammed, if not heavily damaged and clogged with debris themselves. In other words, our current grid is not designed to make it easy for us to bounce back. That suggests that instead of simply making new structures stronger, we should eye improvements that could quicken recovery.

Some lessons have been learned. The trend of replacing old brick schools with newer ones, or retrofitting and remodeling older buildings to bring them up to safer seismic standards, is working. During the Nisqually quake, schools were pretty safe places to be, unlike in China, where many schools suffered catastrophic collapse. Making progress a bit at a time can pay dividends when the "big one" hits.

One problem with the mandatory retrofitting of Seattle's old privately owned brick buildings is moving carefully so as not to make matters worse by requiring property owners to suddenly shell out money they don't have. That could lead some owners to decide to tear down or close down perfectly useable, important, and possibly historic structures.

Mandatory upgrades would have to come with incentives and assistance, like low-interest loans, the waiving of permit fees, tax breaks and credits, etc. Even then, however, it will be a tough sell. The Seattle Scenario found that even in quake-prone greater Los Angeles, public and private infrastructure upgrades were sometimes slow to be adopted.

One idea would be to integrate the retrofitting plans with broader changes to encourage adaptive re-use of older buildings instead of new construction. Keeping older buildings and recycling them for new uses is a key sustainability strategy. Seismic regulations ought to be part of an effort to save and upgrade older structures, not an excuse to level them faster than Mother Nature can.


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About the Authors & Contributors

Knute Berger

Knute Berger

Knute “Mossback” Berger is Crosscut's Editor-at-Large.