Earthquakes in Corvallis? The Willamette Valley is Due for a Big One

In 2011, Corvallis ranked as one of the safest cities in the US, so far as the effects of Mother Nature are concerned. All we really need to worry about is flooding and earthquakes…! Being Beavers, we deal with flooding of various intensities nearly every year. Earthquakes however, are another story, and the Pacific Northwest may be ripe for another big one.

 

Megathrust Quakes

Corvallis, along with the rest of Oregon, Northern California, Washington, and Vancouver Island, B.C. are flanked to the west by the Cascadia subduction zone—an area where the oceanic crust is being forced below the North American continental plate. As these plates slowly move (about 40mm/year), energy builds up over the “locked,” interface between  the plates. When the locked zone releases due to the denser oceanic plate sinking, the stored energy is also released and can cause thrust earthquakes of a magnitude 5 or 6.  These quakes can grow into megathrust earthquakes; these have a magnitude of 8 or higher. Remember that the Richter scale is not linear—a magnitude 8 earthquake is 30 times more powerful than one of magnitude 7, which is 30 times more powerful than a quake at magnitude 6, etc.

Our region is no stranger to quakes that don’t register on the megathrust scale—the Pacific Northwest is riddled with fault lines that underlie many major cities, including Seattle and Portland. Corvallis even has one of Oregon’s larger faults running through the northwestern section of town. Less is known about the seismic potential of these underlying faults; they could be points of weakness during seismic activity or they could never budge.

Scott Ashford, soils engineer at Oregon State says concentrating on these faults may not be the best way to look at things.

“This whole region is going to feel it if the Cascadia subduction zone experiences large movement.  Instead of picturing and avoiding areas with individual faults, understand that this entire region is more of a fault zone; shaking is going to be felt everywhere.”

He adds that those farther east, say, in Bend, will have their own set of problems such as bridge failures, but on the whole, will be better off than the coast and inland valleys.

 

Volcanism

Let’s not forget that the Pacific Northwest has seen significant volcanic activity. Aside from plate tectonics (the most common cause of earthquakes), pressure exerted on rocks by magma directly beneath volcanoes can and does cause quakes. In Oregon, Mt. Mazama erupted around 5,600 B.C. and now holds Crater Lake. Mt. St. Helens erupted in Washington in 1980 and continues even now to produce low rates of seismic activity, steam, and volcanic gases. In Ontario, Canada, Mt. Meager is a constant eruption threat even though it has not erupted in 2,000 years. Recent geothermal energy-related drilling under Oregon’s Newberry volcano has raised the eyebrows of those who consider that particular volcano have a high threat of eruption. So far, no such events have occurred, nor have earthquakes associated with drilling at the volcano been registered.
Shifting Earth

Perhaps the largest concerns associated with an earthquake in Corvallis, regardless of scale, are landslides, dam failures, and liquefaction.

Liquefaction results when movement from an earthquake essentially turns the ground to quicksand or jello. This can result in sunken buildings and damage to utility pipes. The Pacific Northwest has seen liquefaction damage before: during the 2001 Nisqually Earthquake (magnitude 6.8) roads that had been built on soft gravels next to lakes in Thurston County, Washington gave out. Sand boils, geysers that shoot sand, gravel, and water into the air were observed in Thousand Springs Valley, Idaho, in 1983. The quake that caused those had a magnitude of 6.9. Geologists in the Pacific Northwest have mapped the areas most prone to liquefaction and, in Oregon, those areas lie in the coast and valleys due to the saturated, loose nature of the soils there.

Corvallis is potentially at risk from dam failures upstream along the Willamette River.  The North Fork Dam in Philomath is the reservoir for Corvallis’ Rock Creek Water Treatment plant and is owned by the City of Corvallis. This dam is Benton County’s only high potential hazard dam.
The Next Big One

How can you be ready for such an event? Ashford says the best possible place to be may be home. Besides having water and nonperishable food stockpiled, Ashford adds extra prescription medication, fuel, and fire extinguishers to your list of supplies.

“You are more likely to be prepared and to have essentials on hand if you experience an earthquake at home,” comments Ashford. “The gas in your vehicle’s tank may be all you get to have.  Plan to be on your own for at least three days.”

The Japanese have records of flood reports from January 26, 1700 from an “orphan tsunami” generated from an earthquake in the Cascadia subduction zone. Geological evidence shows at least seven quakes have occurred in this zone over the last 3,500 years. This suggests that, on average, a megathrust earthquake happens every 300-600 years.  Let’s see… 2012 minus 1700 equals 312 years. We have officially entered the realm of possibility.

 

Earthquake Disaster Kit

Disasters can happen at any moment, and it is important to be prepared!  Keep a kit at home, in the car, and at work if you can.  The following list was borrowed from www.72hours.org, and is a good place to start for a “Go” bag—made to grab on the run.

*“Go” bag (this is part of your kit, but made to grab in just a second)
*Flashlight
*Radio – battery operated
*Batteries
*Whistle
*Dust mask
*Pocket knife
*Emergency cash in small denominations including change
*Sturdy shoes, a change of clothes, and a warm hat
*Local map
*Some water and food
*Permanent marker, paper and tape
*Photos of family members and pets for re-identification purposes
*List of emergency point-of -contact phone numbers
*List of allergies to any drug (especially antibiotics) or food
*Copy of health insurance and identification cards
*Extra prescription eye glasses, hearing aid or other vital personal items
*Prescription medications and first aid supplies
*Toothbrush and toothpaste
*Extra keys to your house and vehicle
*Any special-needs items for children, seniors or people with disabilities. Don’t forget to make a Go-bag for your pets.

Cascadia Lifeline Programs: A research consortium for disaster planning

With improved technologies to shed light on recent disasters, states are now better able to effectively plan for potentially devastating natural events.

“Through Oregon resilience planning, everyone has realized how much work we have to do.  Now, we have major companies working together to create policies for disasters before we need them,” said Scott Ashford of OSU.

In April 2011, the Oregon House of Representatives unanimously passed House Resolution 3, directing Oregon’s Seismic Safety Policy Commission to “lead and coordinate preparation of an Oregon Resilience Plan that … makes recommendations on policy direction to protect lives and keep commerce flowing during and after a Cascadia (megathrust) earthquake and tsunami.” The Plan is due to be delivered to the Oregon Legislative Assembly by February 28, 2013.

by Lisa Tedder

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