TSUNAMI EVACUATION BUILDING: The proposed Cannon Beach City Hall is one of the first tsunami-evacuation buildings to be be considered in the U.S. and, if approved, could replace the existing city hall with a raised structure that could withstand Cascadia-generated earthquake and tsunami. Image: Jay Raskin, AIA
Plans to build the nation's first tsunami-resistant building are unfolding in Cannon Beach, Ore., in a region that is almost identical, seismically, to the subduction zone that triggered the earthquake and tsunami in Japan last week. Elevated 4.5 meters off the ground, the building would provide an evacuation zone for coastal residents and tourists while also serving as a new city hall.
"The goals are to save lives and provide continuity of government," says Jay Raskin, an architect and former Cannon Beach mayor who is helping to spearhead the design process.
The Pacific Northwest coast is vulnerable to quakes produced by the Cascadia subduction zone, a 950-kilometer-long fault running from northern California to Vancouver, B.C. There hasn't been a Cascadia earthquake since 1700, and many researchers say there is a one-in-three chance a magnitude 9.0 temblor and tsunami will strike in the next 50 years
"It's coming sooner or later," says Harry Yeh, a professor of coastal engineering at Oregon State University (O.S.U.) and tsunami expert who is helping Cannon Beach community leaders with the project.
The building plans were based in part on a 2008 FEMA (Federal Emergency Management Agency) publication, Guidelines for Design of Structures for Vertical Evacuation from Tsunamis. But lessons from Japan may also shape the look and feel of the project, which is still a conceptual design, not an actual building.
The vertical structures that "saved so many lives" during the recent disaster were made of reinforced concrete, many of which remained standing even as wood-frame structures washed away, Yeh says. Japan also has some buildings specifically designed as tsunami evacuation zones.
Earthquake- and tsunami-resistant buildings are not the same, Yeh adds. In the former case wood framing tends to be the better bet, as it can absorb the shaking more effectively than a structure fashioned from rigid construction materials.
But during a combined quake–tsunami, the structure must also be able to withstand the pounding of the waves, or what Yeh describes as "prolonged lateral forces." And, of course, the building must be tall enough that people can escape the rising water.
The Cannon Beach city hall design features concrete stilts reinforced with steel cables supporting a 900-square-meter building. Beams and concrete pilings at the base of the building will help prevent the powerful waves from eroding the foundation.
The building elevation is based on tsunami inundation maps suggesting that 90 percent of all possible tsunamis would generate water depths of 4.5 meters—at the city hall site. But in the aftermath of the Japan quake and the nine-meter waves it spawned, Raskin says he plans to ask the Oregon Department of Geology and Mineral Industries if the assumptions used to create the inundation maps would change.
There are other questions: About 1,600 people live in Cannon Beach, and thousands more flock to the area as tourists. Located at the main beach entrance, the proposed city hall would have room for 1,500 people—who would have about 20 minutes to seek refuge before the deadly waves hit. "How is that going to work?" asks Raskin, acknowledging the challenge of getting so many people inside one structure in such a short time.
O.S.U. researchers are conducting an evacuation simulation study to see how effective the proposed building would be compared with a base case without the building.
Cost is another hurdle. The building has an estimated price tag of about $4 million, about twice as much as standard construction.
In a region that is decades behind Japan in terms of seismic preparedness, the new structure is supposed to be as much a design model as a safe haven, Yeh says. Scientists in the Pacific Northwest only discovered the Cascadia threat about 30 years ago, when a University of Washington geologist located evidence of the 1700 earthquake and tsunami.
As a result, most of the region's building stock and critical infrastructure in the area have yet to undergo seismic retrofits. And according to Yeh, there are hardly any reinforced concrete structures anywhere on the Washington State or Oregon coasts.
In that context the Cannon Beach structure would be "one of a kind," Yeh says. The next step is to secure funding, then hire architects to turn the conceptual design into a real building, Raskin says, adding that as locals watch the tragedy unfold in Japan, interest in the initiative is rising. "There is a growing realization of how underprepared we are and how bad the Cascadia event could be."