Faults discovered on Mount Hood pose earthquake risk

A network of active fault lines have been discovered on Mount Hood, which pose serious danger to the cities of Hood River, Odell, Parkdale, White Salmon, Stevenson, Cascade Locks, Government Camp and the Villages at Mount Hood — as well as Portland — researchers announced Monday.

Geologist Ian Madin of the Oregon Department of Geology and Mineral Industries and Dr. Ashley Streig, an assistant professor of geology at Portland State University, discovered the fault networks while they were analyzing recent high-tech imaging of the area, and followed the discovery with field research to verify their findings.

The fault networks are north, south and southwest of Mount Hood, with the northern fault extending all the way to the Columbia River; and they could potentially trigger a 7.2 magnitude earthquake.

“This would be a crustal earthquake as opposed to the Cascadia subduction zone earthquake Portland has been bracing for,” Streig is quoted in a press release. “Subduction zone quakes are deeper below the surface, they last longer — as long as seven minutes — but they are lower in amplitude. The kind of quake we would get from Mount Hood would be shorter — 20 seconds to less than a minute — and would be strong enough to knock you off your feet.”

Crustal earthquakes are not uncommon in Hood River County, according to information included in the county’s Natural Hazards Mitigation Plan (NHMP), a document that details the area’s prominent natural hazards and lays out mitigation strategies so that the county can prevent future emergencies, or at least minimize and withstand their effects.

The plan lists both crustal earthquakes and the predicted Cascadia Subduction Zone (CSZ) event as among the county’s top 10 natural hazard risks. The CSZ event, however, was ranked third as a priority while crustal quakes were ranked seventh. Both are classified as “moderate” risks.

“The problem with earthquakes is that they not only disrupt the ground, but can also bring secondary problems” such as fires and infrastructure damage to roads and bridges, said Barb Ayers, Hood River County’s Emergency Services manager.

Another concern is that a major earthquake could also close I-84, effectively cutting the county off from outside resources until it can be reopened.

“That’s always a worry, being cut off from the transportation corridor,” Ayers said.

The NHMP was updated earlier this year, but the document was finalized before the additional fault networks were discovered.

While Ayers has not yet seen Madin and Steig’s study, she knew that they were surveying the area around Mount Hood to study the stability of the volcano and knew that there were some faults originating from Mount Hood, so the discovery wasn’t a surprise, she said.

“What makes this place a beautiful place to live is also what makes it a hazard,” she said.

Streig related the potential 7.2 magnitude quake to the 1989 Loma Prieta earthquake, which lasted 10-15 seconds and severely damaged the San Francisco Bay Area, causing approximately 4,000 injuries and up to 67 deaths — except, she noted, the Mount Hood faults are closer to Portland than the Loma Prieta epicenter was to San Francisco, “which means it could be even more damaging.”

“A large earthquake along this fault could have implications for infrastructure including rail lines in the Columbia Gorge and power generation at Bonneville Dam,” and “The Portland metro would experience strong ground motions and could suffer liquefaction damage along waterfront areas,” said a press release.

The need to seismically retrofit county buildings was identified in the NHMP and, while “we certainly have a long way to go,” Ayers said, the county has made progress on retrofitting its public buildings and has projects in the works.

Hood River Fire Department was seismically retrofitted back in, May Street Elementary and Wy’east and Hood River Middle Schools are in the process of being retrofitted, according to information included in the NHMP, and Westside Fire District recently received a large grant to retrofit their building. Parkdale Fire Department has plans to apply for a retrofit grant in 2019.

Buildings with unreinforced masonry, such as historic buildings, are also a concern. These can be retrofitted, she said, but it’s more involved than retrofitting a modern building.

Residents can retrofit their own homes simply by making sure that the structure is secured to the foundation and that the water heater is strapped down, Ayers said.

She recommends that residents keep disaster preparedness kits that they could live off of for at least two to three weeks — these can be bought premade or you could start with a basic camping kit and embellish it with other things you’d need in an emergency, she said.

In an emergency, she also recommended checking in on your neighbors and sharing supplies with each other, adding that the Gorge’s sense of community is one of its greatest strengths.

“There’s no place I’d rather be because in Hood River, we come together and help each other,” she said, “so…don’t worry, we’ll get through it together.”



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