BY BRIAN LIBBY
If you're like me and thousands of others living west of the Cascades, you were left stunned and scared by a recent New Yorker magazine article suggesting that it's almost inevitable that Seattle, Portland and other Pacific Northwest cities will be "toast" (as one Oregon State University seismologist put it) when a massive Cascadia Subduction Zone earthquake arrives, causing what is predicted to be the worst natural disaster in American history.
In the days and weeks following the article, there was a lot of arguing amongst other seismologists and the general public as to just how dire the circumstances are. Is it guaranteed that we'd be hit by a 9.0 earthquake or more? Is it really overdue by decades or could it come in another 75 years? Will we really all be camping outside our houses for over a year without electricity?
Recently I spoke with Bill Steele of the University of Washington's Pacific Northwest Seismic Network to separate paranoia and fear from cold hard facts, and to learn more about just what Portland buildings are under the greatest threat.
From the beginning of our conversation, it was clear that one particular type of building is the most vulnerable: unreinforced masonry, where load bearing walls and other portions of the building like chimneys are made of brick, cinderblock, tiles, adobe or other masonry material that is not braced by reinforcing beams. Steele believes it's just not realistic for us to keep most of them, which is sad, because these old buildings are a huge portion of our city and our architectural character.
"Going back and trying to bring old buildings back up to current standards now that reflect the hazard we face is extremely difficult and in some cases impossible without very expensive base isolation or other strategies," Steele explained. "You wouldn’t employ that unless it was a very special building like a city hall. What you want to do is try to identify those historic structures you absolutely want to keep and find ways of improving their life safety so they don’t collapse on people. And you want to find ways to improve other old buildings or in some cases replace them. One way or the other you hope for all your structures to come up to minimum life safety standard. But it is costly and many of these buildings may have to be torn down after the quake even if the retrofit works. Maybe you were able to evacuate but the building is damaged beyond its reasonable repair. That makes it an expensive proposition to invest in. That’s the challenge: you do you do that? How do you bring everything along?"
But, Steele adds more optimistically, "I think Oregon’s doing a lot of right things. And I know the city is now working on an unreinforced masonry ordinance and involving stakeholders as we speak. I think Portland and Oregon are moving forward, but it’s going to take a significant investment." He says a recent visit to downtown Portland revealed a lot of unreinforced masonry buildings there.
Steele also says our plethora of bridges poses an extra problem. "Some were built to minimum code standards. Oregon didn’t always have as high of a code as Puget Sound. It didn’t adopt Uniform Building Code level 3 [which has more rigid seismic protections] as early as Puget Sound did. There are a lot of important structures that are really quite weak and need retrofitting. I know Oregonians have worked to improve the I-5 bridge to Washington over the Columbia. I think that kind of investment is going to be extremely helpful. Even if you lose one or two bridges, if you have alternatives it doesn’t make you an island. So that’s important."
I asked Steele to further explain the UBC levels, which haven't traditionally been as high in Oregon as in California and Washington. "The Unified Building Code was one of the first with seismic standards built in based on the hazard. UBC [level] 3 is essentially designed so the building will not collapse when subjected to 30 percent of the force of gravity in horizontal shaking," he said. "UBC 4 is designed to withstand 40 percent without collapse. It doesn’t mean they will always be safe, but they won’t kill people. That’s the first level of engineering that you want to achieve, your base level. Nowadays Oregon and Washington have adopted the International Building Code, which has some different ways of approaching these standards. It’s more adaptable. It takes the USGS seismic hazard maps and takes the probable shaking levels a building will receive on a given site and establishes level 4’s criteria based on that."
Why stricter standards for Seattle? "Because Seattle has a big crustal fault that has produced quakes. It’s uncertain in Portland with the Eastbank Fault. We both have the Cascadia Subduction Zone, but Seattle has more possibility of local quakes. If you go down to Eugene it will probably be a bit lower than Portland from all sources. It’s all kind of grounded on the best science available, but in some cases like crustal earthquakes we have less experience with it. We have a 10,000-year history with the Cascadia Subduction Zone, but less info about the crustal faults. Many have one earthquake we know about from paleo-seismologists. It’s kind of hard to predict based on one quake in the past."
Steele also said that more rigid codes are not always the answer. "You don’t want to make the codes unnecessarily strict so it unrealistically increases the cost," he explains. "You also don’t want someone to make the investment and then have it destroyed during a quake. That’s what they’re working on with the IBC, to find the level best suited for the areas. If you’re a police station or a hospital, you just build to a higher performance standard than the basic minimum code. I think key bank is one of the first to do so in the private sector in Portland. They wanted to use their bank after the earthquake. These performance-based standards are coming into play. UBC can say, here is the minimum life safety value. What level do you want to achieve? It becomes much more tunable, if you will."
Does this threat of a massive Cascadia Subduction Zone earthquake make Oregon a more dangerous earthquake zone than California? Steele says no. "California has a much higher hazard. They have about two-thirds more risk than we do," he says. "That’s based on the frequency of big quakes, how close their built environment is to active faults like the San Andreas and the Hayward. There’s a whole suite of them. They have more deformation, more quakes, bigger faults near their population centers. It makes sense that they need to build to a higher standard."
If Portland were to have a large crustal earthquake, though, that might be different. "If you had a magnitude 7 on the Portland Hills fault, the impact might be greater because you have more vulnerable buildings than San Francisco does," he says. "In that sense, when the earthquake does occur it’s going to be every bit as bad. Buildings like hospitals should consider that standard or even more. We're only talking about a small percentage of the building’s cost. It’s something worth thinking about, so your hospital is functional after the earthquake. And I think with schools it’s something to consider. And it’s a question: are we going to keep this old reinforced masonry structure? We can’t build the building anywhere near where it should be. Maybe we should consider taking it down and building a modern structure. It’ll be much safer for the children and actually may cost less than retrofitting the old one. Those are the decisions that have to be made."
As dire as the forecast may be, when I told Steele that I worried about all of Portland's historic homes being destroyed, he took less of a fatalistic tone. "It’s less of a problem for a number of reasons," he says. "One, wood framed structures tend to perform pretty well in earthquakes. Many aren’t bolted their foundation though. But for a small percentage of the cost of your home you can do so, and you can create what’s called a pony wall so the house won’t rack over without any reinforcement and drop onto its foundation. You strengthen that and bold to the foundation, and you’ve made a good improvement. It’s also important to strap down your hot water heater so it won't tear the gas lines from your heater."
"What I’m not sure about," he adds, "is if the ground will shake enough during a Cascadia quake to shake homes off their foundations. It’s difficult to anticipate with any accuracy how strong the shaking’s going to be in any neighborhood. There’s great variability. That said, it would probably be around 20 percent shaking. It takes 30 and above before houses are shaking off their foundation. Crustal quakes, things come off their foundations fairly easily. But that’s not the most common hazard. Those really high accelerations are probably not going to happen."
Perhaps the biggest takeaway from our conversation is that the New Yorker article can provide a wake-up call that saves lives.
"It takes good planning and a focus of our resources," Steele says. "If it’s something we really love, those areas should get some public investment to do what’s necessary to protect those buildings. Secondly, the public has some skin in the game. We can say, 'We want you to spend lots of money to protect these structures.' The public needs to look for ways to help property owners make those improvements and share some of those costs so it’s doable. You don’t want buildings abandoned so no one can afford to do something. But really tearing down some old buildings that aren’t iconic is really the best option."
"It’s a balancing act, isn’t it? It’s trying to take advantage of the opportunities. After the quake a lot of unreinforced masonry buildings are damaged, and some of those you’ll want to rebuild. But there would be a lot of federal dollars and other resources that would flow in that would allow some significant improvements. There are advantages you can achieve when part of the deck is cleared."
"You can’t do everything," Steele says. "I just wish we were a little more systematic about strengthening our infrastructure. Seattle has failed so far to pass an unreinforced masonry ordinance. Hopefully Portland will have a little better luck. You’re still looking at ways of helping landowners meet the requirements. The engineering part is the simplest. It’s about how you implement this and bring everyone alone. It’s everybody’s problem. It needs to be everyone’s solution."