Scientists have estimated that there is a one-in-three chance that a mega-earthquake will hit the Pacific Northwest in the next 50 years.
[social_buttons]However residents of the small town of Cannon Beach on the Oregon coast are well aware they’re in the firing line of an earthquake and the ensuing tsunami, and they’re preparing. Wokring together with experts from Oregon State University, the Oregon Department of Geology and Mineral Industry and local residents, the small town is looking to create a town hall that will act as a tsunami proof building.
“In all but the most catastrophic scenarios, it’s been estimated that the water level from an incoming tsunami at the site we propose to build the new city hall could be up to 15 feet,” said Jay Raskin, a local architect and one of the community leaders working to create the new structure. “We think this building could shelter at least 1,500 people. It will cost more, but so far there has been a pretty positive public reaction to the idea.”
Research conducted by Oregon State University marine geologist Chris Goldfinger and his colleagues has cast a new face on the Northwest’s seismic history, pointing out that earthquakes of a magnitude 8.2 or higher have occurred 41 times over the past 10,000 years.
These earthquakes all originate from the Cascadia Subduction Zone, a massive convergence of the Juan de Fuca and North America tectonic plates that stretches from northern Vancouver Island to northern California.
“What we’ve found is that Cascadia isn’t one big subduction zone when it comes to major earthquakes,” Goldfinger said. “It actually has several segments – at least four – and the earthquake activity is different depending on where a quake originates. The largest earthquakes occur in the north and usually rupture the entire fault. These are quakes of about magnitude-9 and they are just huge – but they don’t happen as frequently.
“At the southern end of the fault, the earthquakes tend to be a bit smaller, but more frequent,” he added. “These are still magnitude-8 or greater events, which is similar to what took place in Chile, so the potential for damage is quite real.”
“Perhaps more striking than the probability numbers is that we can now say that we have already gone longer without an earthquake than 75 percent of the known times between earthquakes in the last 10,000 years,” Goldfinger said. “And 50 years from now, that number will rise to 85 percent.”
The last major quake to emanate from the Cascadia Subduction Zone was in January 1700 which created a tsunami that made its way to Japan. And though the records of what happened in Japan are much more extensive than those in the Pacific Northwest, Goldfinger’s studies have suggested the physical alteration to the coastline was stunning.
The other problem facing the residents of the Pacific Northwest is the possibility that major earthquakes occur in clusters. A thousand years could go by without a major event and then a series of earthquakes could hit every 250 years or so.
“We’re just starting to understand the whole idea of clusters and there isn’t consensus on whether we are in one or not,” Goldfinger said, “but that possibility does exist, which further suggests that we may experience a major earthquake sooner than later.”
So it’s not surprising that the residents of Cannon Beach want to be prepared.
“Every community from Cape Mendocino in California to Vancouver Island in Canada is vulnerable to some extent to the Cascadia subduction zone earthquake and tsunamis,” said Patrick Corcoran, an OSU Sea Grant Extension hazards outreach specialist. “This is arguably the greatest recurring natural hazard in the lower 48 states. Our cities are not engineered to deal with it and our residents are not prepared for it. We need evacuation routes, assembly sites, public education and outreach. And in some places, we need vertical evacuation structures.
“The only way to potentially save thousands of lives is through more education and better engineering.”
The current conceptual design of the building has it at 9,800 square feet with a cost of $4 million. And though public opinion is high and funding is being sought from the federal government, the challenge is still trying to bring the costs down. The proposed structure is twice as much as a standard structure would be to build.
On top of that is the problem that no one has been able to study exactly how a building can survive being hit by a tsunami. Japan is the only country in the world with “tsunami proof” buildings, but these haven’t been put to the test yet. Subsequently, engineers at OSU are testing a proposed model of the structure in their Tsunami Wave Basin, the most sophisticated facility of its type in the world.
“We’re heading in the right direction, but this is new territory,” said Dan Cox, a professor of coastal and ocean engineering at OSU. “There’s a lot we still need to learn about the impact of forces from waves, cars, collapsed buildings and other debris, and just how strong a building must be to resist that. But our tests should help add a higher degree of confidence in this design.”
There are a number of other projects being looked at across the Pacific Northwest. Washington state’s Long Beach peninsula is looking at building a series of artificial hills that would be high enough to stand above tsunami waters, as well as serve a purpose in the meantime as picnic areas or ocean viewing platforms.
“We probably would have built these communities differently if we knew 50 years ago what we know today,” Corcoran said. “But it’s also worth noting this isn’t just their problem. This coastline is very beautiful and people come from all over the world to see it, many thousands of them on nice days. This earthquake is coming. So we all have a stake in doing what we can to prepare for it.”
Images: Oregon State University