Earthquakes in the Northwest
Warner Pacific College
June 22, 2011
“There was a shaking, jumping up and trembling of the earth beneath, and a rolling up of the great waters.” –From Native American oral tradition.
In January 1700, one of the largest earthquakes in history struck off the Oregon and Washington coast. It is believed by researchers to have been a magnitude 9. This powerful quake caused a 30’ high tsunami to hit the low-lying coastal areas, causing tremendous destruction. The Native American tribes in that vicinity have passed down oral records of this event through the present day. These tribes believed the earthquake was a result of a battle between the Great Thunderbird and a Whale.
According to The Neighborhood Emergency Team Participant Manual (2008 p.2) Scientists have determined that the earthquake in 1700 was a “subduction zone” quake. Subduction zone earthquakes occur when great crustal plates slide underneath another plate. The research indicates that these quakes occur on average every 300-500 years. The most recent one was the January 26th, 1700 quake.
The tectonic plates that threaten the Pacific Northwest are known as the Cascadia Subduction Zone. There are two massive tectonic plates that are colliding with each other. These plates are called the Juan de fuca plate, which stretches 750 miles from British Columbia to Northern California, and the North American Plate, which is shifting westward. The collision of these plates sets the stage for potentially devastating quakes. In the spring of 2008, a series of previously unknown faults; a fracture in the continuity of a rock formation caused by a shifting or dislodging of the earth’s crust, was discovered after a swarm of undersea quakes that occurred 140 miles southwest of Newport on March 30th. This swarm of earthquakes registered a magnitude of 3 and 4. Experts were puzzled because the quakes appeared to be caused by volcanic activity coming from the middle of the Juan de fuca plate. Earthquakes that are usually the result of volcanic activity happen along the edge of tectonic plates, not originating from the middle like this one appeared to be. The Juan de fuca plate is caught between two larger plates that are squeezing it. In the article, Previously Unknown fault caused earthquake swarm of Oregon’s coast (2009). William Willcock, a marine geophysicist and professor of oceanography at the University of Washington, said there is emerging evidence that earthquakes and volcanic eruptions separated by hundreds of miles away my be interlinked.
What is the likelihood of Oregon getting hit by another “Big One?” Scientists predict that we have between a 10 and 15 percent chance of experiencing a magnitude 9 quake within the next 50 years. This of course is just an estimate, as it is practically impossible to predict when the next major earthquake will strike. Scientists have been studying the past patterns of earthquakes in hopes of recognizing predictable patterns in the hopes of improving their forecast of future earthquakes.
I will never forget the earthquake experiences I have had here in Portland. The first one occurred back on March 25, 1993. It was early morning, and I was getting ready for work, when all of a sudden the whole house began to shake. It sounded as if a freight train was driving through my backyard! As quickly as it started, it stopped. Fortunately, there were only minor reports of injuries and property damage in the Portland area. My second quake experience occurred on February 28, 2001. I was at work when this quake struck. The office building I was in started to slowly shake. Immediately, people began to run for the exits, which I learned much later on is not necessarily the wise thing to do! Luckily, none of my co-workers were injured, though this quake left 400 injuries between Seattle and Portland and caused 2 billion dollars in property damage. In the article, A region at risk geologic dangers shared by Portland and Seattle make last week’s message clear: we’ve been warned, Hill (2001). The author states that scientists said the amount of energy unleashed in this quake was the equivalent of three times the power of the atomic bomb that was dropped on Hiroshima. This quake actually shoved Seattle about two-tenths of an inch to the northwest!
Both Portland and Seattle sit on top of the North American tectonic plate, which overlies the Juan de fuca plate. Both cities are at risk of earthquakes. Scientists have identified three large faults in Portland: The East Bank fault, the Portland Hills fault, and the Oatfield fault. The East Bank fault underlies Central Catholic and Benson High Schools, Lloyd Center mall; which I work a few blocks away from, The Oregon Convention Center, Rose Garden Arena, Mocks Bottom, and University of Portland. The Portland Hills fault runs from the northern edge of Forest Park, goes along the foot of Portland’s West Hills and beneath Portland State University, crosses the Willamette River and heads southwest to Milwaukie. The Oatfield fault runs west of Skyline road from Germantown Road through Bonny Slope. Much of Portland’s soil is comprised of lose sediment deposited by gigantic ice-age floods that swept down the Columbia River about 15,000 years ago. This type of loose soil amplifies the shaking during an earthquake. How would our infrastructure hold up in the face of a major earthquake? It is estimated that 64 percent of Oregon’s bridges would be destroyed. The Coast would be entirely cut off. All connecting highways through the mountains would be susceptible to landslides. Half of Oregon’s current schools are not up to earthquake code, and there are still many older buildings constructed of unreinforced masonry, which would probably collapse during a quake. Estimates of casualties could well be in the thousands. Oregon’s energy infrastructure is very vulnerable, specifically our fuel pipelines, petroleum storage tanks, ports, and transmission lines.
What can we do as individuals to prepare for such a disaster? You can start by preparing a 72-hour survival kit that contains food, water, a battery operated radio, flashlights, and some basic tools to shut off water and gas lines. The Portland Fire Bureau offer an intensive eight week course in emergency preparedness that I have personally gone through and highly recommend. That training could save you and your family’s life. You will also be able to help those in your community as well.
When it comes to the destructive power of Mother Nature, we are like little ants in the face of a hurricane, earthquake, or tsunami. We cannot control many of the major events that shape the geology of our planet, but we can learn to appreciate the precious gift of life that we have been given by The Creator.
Hill, R. L. (2001, March). A Region at risk geologic dangers shared by Portland and Seattle make last week's message clear: we've been warned. Retrieved from http://www.oregonlive.com/special/earthquake/index.ssf?/news/oregonian/01/03/lc_11quake04.frame
Rojas-Burke, J. (2009, October). Previously Unknown fault caused earthquake swarm off Oregon’s coast. Retrieved from http://www.oregonlive.com/news/index.ssf/2009/10/previously_unknown_fault_cause.html
Withgott, J. & Brennan, S. (2011). Environment, The Science Behind The Stories. San Francisco, CA: Pearson Education Inc.
Neighborhood Emergency Team Participant Manual. (2008). Portland: Office of Emergency Management.