Experts: Fault lines difficult to detect, assess

Photo Credit: MARK MILLER - St. Helens City Hall is among the local buildings that could collapse in a major earthquake. State expert Ian Madin said unreinforced masonry is especially vulnerable to quake damage.Is south Columbia County prepared for a major earthquake?

The short answer is “no” — but there are measures that both individuals and agencies can take to be ready.

A magnitude 6 earthquake rattled California’s Bay Area early Sunday, Aug. 24, damaging buildings and streets and injuring about 200. While the fault system on which the quake occurred is separate from the faults in northwest Oregon, the event serves as a reminder of the geologically turbulent foundation upon which our lives rest.

“There’s more we don’t know about the faults in the region than what we do know,” said Bill Steele of the Pacific Northwest Seismic Institute, which is based in Seattle, on Monday. “We don’t have them all well-mapped.”

But, Steele said, just because seismologists do not see the faults does not mean they aren’t there — obscured by thick bedrock in some places, like the high basalt shelf upon which much of south Columbia County sits.

“It would be no shock or surprise to put a magnitude 6 earthquake similar to what occurred in California anywhere in western Oregon,” Steele said. “There are faults in the crust near every city, probably, most every city in western Oregon that could produce a magnitude 6 earthquake. We don’t know where all of those are, by any means.”

Ian Madin, a lead scientist studying earthquake patterns at the Oregon Department of Geology and Mineral Industries, said it is difficult to identify earthquake risks ahead of time.

“Earthquakes like this Napa one ... it occurred on a fault that wasn’t really well-known or considered one of the more dangerous ones down there,” said Madin, referring to Sunday’s quake in California.

The big one’ is coming

Oregon is also threatened by the specter of a major earthquake emanating from the Cascadia subduction zone, a massive fault system off the coast of northern California, Oregon, Washington and British Columbia. The last big quake associated with that fault took place in 1700, more than a century before the Lewis and Clark Expedition extended American influence into the Pacific Northwest — and decades before American independence in 1776.

But while much ink has been spilled about the earthquake risk, Madin dismissed the idea that the region is “overdue” for “the big one,” as many seismologists refer to the hypothetical future quake.

“The average time between those earthquakes is 540 years,” Madin said. “So we’re not even up to the average time yet [since the 1700 earthquake]. So it’s quite incorrect to refer to that as ‘overdue.’”

Photo Credit: COURTESY OF THE WASHINGTON STATE DEPARTMENT OF NATURAL RESOURCES - A collapsed walking path in Olympia, Wash., showing the extensive damage caused by the 2001 Nisqually earthquake. One fatality and hundreds of injuries were attributed to the magnitude 6.8 temblor, which was felt throughout most of Washington, northwest Oregon and southwest British Columbia.Smaller earthquakes than the 1700 event, which has been estimated as about a magnitude 9 quake, are far more common in Oregon than the massive quakes that have ripped through Chile, Japan, Central Asia and the Indian Ocean in recent years.

However, even earthquakes much closer to the size of Sunday’s magnitude 6 quake in Napa, Calif., can cause major damage.

An earthquake that devastated Christchurch, New Zealand, in 2011 was recorded at magnitude 6.1. Nearly 5,800 people died in a magnitude 6.3 earthquake in Indonesia in 2006. The deadliest quake of the century to date is believed to be the 2010 Haiti earthquake, which registered as a magnitude 7 event.

Steele said Oregon has experienced quakes of a size similar to the Nisqually earthquake, which struck near Olympia, Wash., in 2001 as a magnitude 6.8 quake and was felt throughout northwest Oregon, “scattered through the state” in the past.

“They’ll happen in the future, and they’ll happen in more populated areas in the future,” said Steele.

State, county not prepared

The destructive earthquakes in other parts of the world, from Indonesia to New Zealand, were calamities for the unprepared communities they affected — but a report delivered to the Oregon Legislative Assembly last year by a team of specialists suggests Oregon is in poor shape to respond to a major quake of its own.

The Oregon Resilience Plan paints a grim picture of the state’s ability to withstand and recover from a massive earthquake. According to the report, it could take as long as three months for power to be restored throughout the region of the state between the Coast Range and the Cascades — and up to a year for drinking water and sewer services to be restored. Even top-priority highways, including Highway 30, could take up to a year to be just partially restored.

In an executive summary of the report, the authors wrote, “Resilience gaps of this magnitude reveal a harsh truth: a policy of business as usual implies a post-earthquake future that could consist of decades of economic and population decline — in effect, a ‘lost generation’ that will devastate our state and ripple beyond Oregon to affect the regional and national economy.”

Photo Credit: FILE - The Sauvie Island Bridge, built less than 10 years ago and maintained by Multnomah County, is one of the few bridges in the Portland metropolitan area built to withstand the seismic forces of a major earthquake. Multiple state assessments and reports warn that significant portions of Oregon's infrastructure, including Columbia and Willamette river bridges throughout the state, could fail if a large quake strikes the region.Madin’s outlook for how south Columbia County might hold up in the event of a large earthquake was mixed.

On one hand, the basalt bedrock in St. Helens provides sturdier footing for structures than buildings built on softer soil or sand, which may liquefy in the event of an earthquake, Madin said. But Columbia County also has relatively little new construction, and older buildings are vulnerable to earthquake damage.

Stone and brick buildings — like St. Helens City Hall and the historic Columbia County Courthouse — are particularly susceptible to collapse in a major earthquake, according to Madin.

“It is possible to retrofit buildings like that, but it is very expensive,” said Madin, explaining, “Unreinforced masonry just inherently doesn’t have the strength and flexibility needed to withstand an earthquake.”

A 2006 study cited last week by Peter Courtney, president of the Oregon State Senate, lists St. Helens High School, St. Helens Middle School and Scappoose Middle School among school buildings deemed to run a high risk of collapsing due to a large earthquake.

Wide-reaching impacts

Oregon updated its building code in 1994 to require new construction be built to higher seismic standards. However, many bridges in the state — including most of the Willamette River crossings in Portland, as well as crossings over the Columbia River like the Astoria-Megler Bridge — predate the code and could fail in a major quake.

Madin said roadways and railroads are especially vulnerable to earthquake damage.

“Because all you have to do is cut the road or the railroad in one place and it’s not usable, they’re much more vulnerable to that sort of thing than a building,” Madin said.

Photo Credit: COURTESY OF THE OREGON DEPARTMENT OF TRANSPORTATION - The aftermath of a landslide that collapsed a stretch of Highway 30 east of Clatskanie in 1996. The Oregon Department of Transportation referred to the ruination as 'complete roadway failure' and said it took 21 days to fully restore service. This particular slide was blamed on heavy rain, but earthquakes can cause landslides and rockfalls as well.An assessment of potential “lifelines” in Oregon’s surface transportation network by the Oregon Department of Transportation in May 2012 listed Highway 30 as a first-tier route in case of a major earthquake — higher than both Highways 26 and 217, major transportation routes in the Portland metropolitan area, and equal to Interstate 5.

But landslides in 1996 and 2007 were enough to shut down parts of Highway 30 near Clatskanie for days. It took three weeks to reopen the highway after the 1996 slides, according to ODOT.

A report produced by ODOT last year suggests retrofitting and upgrading Highway 30 between Portland and Astoria to better withstand earthquakes and landslides could cost more than $60 million.

Courtney, the Senate president, has proposed $200 million in bonds for seismic retrofitting in schools, which could conceivably benefit Scappoose and St. Helens. Some bridges have also been rebuilt or retrofitted in recent years to better withstand quakes, including the Sauvie Island Bridge, which was just reconstructed last decade.

Preparing for the worst

Vincent Aarts, the county’s emergency management coordinator, said, “The Cascadia event, should it happen, could be of such a large magnitude that it could pose serious challenges, regardless of the amount of preparation we could do.”

Aarts said he could not offer any cost estimates for what it would take either to prepare Columbia County for a major earthquake or recover from one. But he said the prospect of a damaging quake is taken seriously by the county Department of Emergency Management.

“We do identify some of these areas that require mitigation, but not all goals have been met,” Aarts explained. “It’s a matter of planning ahead of time and then working diligently to get to where we want to be.”

But while preparing local communities, the state and region for “the big one” is a costly and laborious enterprise, Aarts and Madin said individuals can ready themselves as best they can. Madin recommended that homeowners discuss an emergency plan with their families, look into seismic retrofits that could be made to their chimneys and other vulnerable structures, and put away a few weeks’ worth of supplies.

“It was, for some time, conventional wisdom that residents of our county prepare a 72-hour kit,” Aarts remarked. In the case of a magnitude 8 or magnitude 9 earthquake, he added, “We may even need longer-duration emergency kits. Some of the verbiage I’m hearing from Oregon Office of Emergency Management is food and water for three weeks.”

For his part, Madin said, “If you’ve taken steps to get your self-sufficiency kits, to get your family plan ... you’ve really done what you can and what you need to do. And then people should get on with their lives and not worry about it so much.”

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