Oregon Tsunami Maps Dangerously Out Of Date | KUOW News and Information

Oregon Tsunami Maps Dangerously Out Of Date

Sep 27, 2015
Originally published on October 1, 2015 10:04 am

Oregon is unprepared for the tsunami that could follow a Cascadia Subduction Zone earthquake. The megaquake has a 1-in-3 chance of hitting in the next 50 years.

An analysis by OPB earlier this year found that about a third of schools, hospitals, police and fire stations along the Oregon coast are within the potential tsunami zone.

RELATED: Search What Critical Infrastructure Might Be Affected In Your Community.

But the official maps of Oregon's tsunami inundation zone are 20 years old. They contain a single regulatory line. On one side, coastal communities can build new schools, hospitals, police stations and critical infrastructure. On the other side, they generally can't.

A lot has changed in 20 years, however, including the sophistication of computer modeling.

The Oregon Department of Geology and Mineral Industries, known as DOGAMI, created new tsunami maps in 2013.

“The difference is quite dramatic,” said Interim State Geologist Ian Madin.

These new maps have no legal standing, Madin said. They're used to establish evacuation routes, but not to regulate new construction. For now, they merely provide more accurate information communities can elect to use or ignore.

Coastal communities would take a big step forward in preparing for the coming megaquake if they adopted newer, up-to-date tsunami inundation maps.

The inundation zone mapped in 1995 is, more or less, a crude calculation of a tsunami's impact after an 8.8 magnitude Cascadia earthquake.

“This is an important consideration, because we know that earthquakes sizes on Cascadia can range from 8 to 9.2,” Madin said. “The size of the tsunami totally depends on the size of the earthquake.”

RELATED: The Difference Between An 8.8 And 9.0 Earthquake Is Huge

Newer tsunami maps are modeled on five earthquake sizes — small, medium, large, extra large and extra extra large. Geologists call them the "T-shirt sizes."

DOGAMI charted out every large earthquake along the Cascadia Subduction Zone for the past 10,000 years. Although the 1995 map is based on the most likely earthquake to strike, the information it used to determine the tsunami's scope is now viewed as dated.

Tsunamis are shaped by more than the strength of earthquakes. They're affected by factors like how a fault slips, as well as seafloor and land geography, and the movement of the water when it hits the shore.

"There's a huge, both quantitative and qualitative, difference between the new data and the old data," Madin said. "The old data was literally eyeballed onto a map with a pen by somebody who was very knowledgeable."

The new data was created with more sophisticated computer modeling and information obtained from high resolution LIDAR topography, which measures the elevation of the ground to within inches.

Part of the challenge is that every earthquake has a completely different pattern of movement. But with the new data, DOGAMI was able to create better models of how a tsunami might behave in various situations.

It's up to DOGAMI's governing board, not state lawmakers, to determine the regulatory line marking the state's tsunami inundation zone. Madin said he is confident one of the new maps will soon become Oregon's new legal standard -- most likely the large earthquake, or "L," scenario.

Before making a change, however, there's a period of public outreach. Funding issues have complicated that.

Some people in the earthquake preparedness community are critical of how long it's taken DOGAMI to adopt an updated standard. They include Jay Wilson, chair of the Oregon Seismic Safety Policy Advisory Commission. He said he thinks the implementation of a new regulatory line should have been a formal part of completing the new maps, not what he calls an "afterthought."

"In my opinion, the formal release of the new tsunami inundation 'L' line should have been scheduled and funded as a part of the process of updating the original 1995 line, so that there would be no lag time for implementation and application towards zoning and land use planning in coastal communities," he wrote in an email to OPB.

Until a decision is finalized, the question for communities on the coast is which line they want to advocate for — S, M, L, XL or XXL?

“It’s a question of how much risk are you willing to tolerate,” said Madin.

“If you pick the XXL, we are generally able to say that there’s 99 percent chance that if you are above that line you will never get wet. If you choose the XL there is a 98 percent chance,” he said.

If you're outside the large line, there's a 95 percent chance you'll stay dry, according to DOGAMI. The medium line is more like 79 percent.

All evacuation maps use the up-to-date XXL model. But when it comes to regulatory decisions, things are far more complex.

Madin said he believes DOGAMI's governing board will adopt the "large" earthquake and tsunami scenario as the new regulatory standard next June. That change was provisionally approved in 2013.

The current tsunami regulatory line is closest to the "medium" scenario.

"Going from the current line to a 'large' scenario is something like a 30 percent increase in the number of structures that are in the (inundation) zone," Madin said.

Critical structures already in the new zone wouldn't need to be rebuilt. However, the construction of new hospitals, schools, and police stations would be largely prohibited there.

These changes are hardly theoretical.

If the new "large" regulatory line had been adopted sooner, for example, it would have prevented Gold Beach from rebuilding Curry General Hospital a few blocks away from the ocean. Voters passed a $10 million bond measure to pay for the project.

"Those maps should have been implemented at that time," said Wilson, the Oregon Seismic Safety Policy Advisory Commission chair. He said he sees the location of the future hospital as a state failure and an important lesson. "We need to be much more out in front of these decisions in the future."

Wilson acknowledged Madin's commitment to getting the tsunami line changed. However, Wilson said, "We're still waiting for them to be officially implemented."

There are success stories on the coast. Towns like Cannon Beach are raising awareness about the threats with innovative initiatives. Last month, residents participated in the inaugural “Race The Wave” 5K.

Lincoln County taxpayers passed a $63 million bond that moved Waldport High School out of the tsunami zone and on to the top of a hill. The seismically-fit building doubles as a meeting place for the town. Lincoln County also has the facilities for a makeshift command center.

However, a similar proposal for Seaside schools fell flat in recent elections. The reason could have been the steep price tag. At $128.8 million, property owners faced a tax hike of $1.82 per $1,000 valuation. For a $200,000 property, for example, the tax would have been $364. Doug Dougherty, the superintendent at the Seaside School District, speculates it might also be because nearly two-thirds of homes in the town are owned by people who aren't permanent residents.

“We know that we had many people who had relatives and friends who lived out of our area, and basically they changed their voter registration so they would be able to vote on the ballot against the school district," he said. "They don’t live here and didn’t want to see their taxes increase”

Ed Jahn contributed reporting.


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