If you live or work in the Pearl District, Downtown, Buckman, Overlook or SE (to name a few), you do.
As we’ve heard, fair Oregon and the Cascadia subduction zone is well overdue for it’s next major earthquake. On average, a major quake ruptures in our area every 243 years The most recent on January 26, 1700— a quake so big it generated a tsunami that damaged coastal towns in Japan. That was 316 years ago, so yea… we’re overdue.
If dealing with the Cascadia weren’t enough, Portland also straddles three crustal faults that stretch the length of Stumptown: the Oatfield Fault west of the northwest hills; the East Bank Fault, following the Willamette downriver from Oregon City, and the West Hills Fault which parallels Forest Park into downtown Portland. These shallow earthquakes produce shorter durations of strong ground shaking, but may be more damaging because they are located right in and around Portland.
Wherever our next earthquake originates, the damage will be exponentially worse on top of Portland’s liquefaction zones.
Portland’s topography is a bit different today than it was 150 years ago. Since pioneers founded our lovely city, we’ve dug and shifted the soil to bring civilization to the Willamette. We’ve reclaimed, flattened, raised, and generally altered our environment. It’s the Pioneer Spirit!
Portland filled in marshes and eddies as it grew with tons of mill waste, sawdust, dredge, gravel, debris and garbage. We filled in the mouth of Enois Creek in Marquam Gulch, Blackiston's Lake north of Burnside; even Waterfront Park sits on top of 50 feet of fill.
The bridges spanning the Willamette required more riverbank for foundations. The construction of the massive Harbor Wall in 1920s and the creation of port facilities moved the Willamette’s west shore eastward. The low areas on the east side of the river were filled in, as were Mocks Bottom and Swan Island. As we poured in fill, the east bank of the Willamette kept moving westward.
Those filled-in parts of the city are built on soil that isn't as densely packed, so they are much more susceptible to damage. When this soft soil starts moving during an earthquake, it becomes like quicksand (liquefaction) and can shift the the structural integrity of buildings, leading to increased damage and water and gas pipes bursting.
If you live in one of these areas, it is even more important that you are prepared to act (and potentially evacuate) quickly. I have the Earthquake Bag underneath my bed because it has everything I need to get out of my building in under a minute. I want to know I'll have food and water, an emergency radio, first aid kit, tools for evacuating, helping others evacuate, and surviving the first few days after the next major earthquake. Take a look at the map and find where you live and work…
What is liquefaction?
It's when the strength and stiffness of a soil is reduced by earthquake-shaking or other rapid loading. It occurs when the space between individual particles of soil is filled with water, exerting a pressure on the soil that influences how tightly the particles are pressed together. Prior to an earthquake, the water pressure is relatively low. However, the shaking can cause the water pressure to increase to the point where the soil particles move easily with respect to each other (imagine shaking a bowl of oatmeal).
Liquefaction has been responsible for tremendous amounts of damage during earthquakes around the world. The 1989 Loma Prieta quake in San Francisco devastated neighborhoods with loss soil composition, and led to 1990 Seismic Hazards Mapping Act, requiring the California Geological Survey to map and publish liquefaction risk areas. Knowing is half the battle and allows us to fortify the buildings that are in the most compromising locations.
We obviously recommend the Earthquake Bag- I like it because it allows me to optimize for how many people I’m preparing for (1-5 people), gives me different price options (I recommend the Elite bag), and includes a survival guide and info on how to approach earthquake prep and aftermath.
Whether you live in a liquefaction risk area or not, make sure that you have the tools you need, food and water, and a plan by the door or under the bed. We know Portland and the Northwest will experience major earthquakes again, and we are smart enough to be prepared for it.