Scientists, geologists, politicians, and just about every one else in between have been highly focused on the Cascadia Subduction Zone for the past several years – and rightly so. It poses a tremendous risk to the well being of the Pacific Northwest. But lurking right beneath our own feet here in the Portland area, are the makings of damage that would make Hollywood envious. The Rose City, with its mass of aging bridges, skylines, and infrastructure, is built on several faults that can not be overlooked for the magnitude of destruction they have the potential to mete upon this beautiful city of ours. These are relatively shallow faults, known as crustal faults or Strike – slip faults. There are three main faults: The Portland Hills Fault running from just outside Scappoose to roughly the Gladstone / Oregon City area. The East Bank Fault that runs parallel to the Willamette River’s east bank from the University of Portland down to inner SE Portland. Finally, The Oatfield Fault that runs on the west side of the West Hills, from Sylvan Hill through Bonny Slope over to the crest of Germantown Road.
Even though there has been some seismic activity in the Portland area, there wasn’t much understanding as to why. It was originally believed that there was only one fault in the Portland area, but in depth studies the USGS in 1992 revealed that there were two other faults, the East Bank Fault and the Oatfield Fault. It is now believed that the East Bank Fault is the largest of the three and has the most potential for damage of the three.
The history of these faults is not quite as well known as the Cascadia Subduction Zone due to a lack of physical evidence. There are few tangible references of any recent quakes produced by any of the three faults. Part of the reason for this is the vast amount of development that has taken place over the course of the last 150 years, thick vegetation, rugged topography, and erosion. Much of the soil in the are is leftover sediment from the Missoula Floods from between 13,000 – 15,000 years ago – much of which may have eroded away, taking with it any seismic evidence that may have been there.
Finding such evidence has been the Raison d’ Etre for several scientists, who have spent years looking. The ‘Ah-ha!’ moment came in May, 2001 at Rowe Middle School in Milwaukie, OR when geologist, Ian P. Madin noticed anomalies in sediment at the school during excavation for a retaining wall. The excavation was the perfect opportunity for Madin to examine the sediment, in his search for evidence of seismic activity in the Portland Hills Fault. Madin noticed deformed layers of soil in the excavation site, which ultimately was the evidence he was looking for. It was a matter of being in the right place at the right time for Madin. He and his peers all agree that more research needs to be done, but also concur that, “the earthquake risk for Portland just got ratcheted up a notch.”
The disturbed soil showed evidence of seismic activity, possibly as far back as 10,000 years ago. Though this time frame seems extremely distant to the normal lay person, to a geologist, this is recent enough for them to list this as an ‘active’ fault line. The lack of any other evidence both provides relief and worry to seismologists. Relief, as it shows extended periods of time between earthquakes, and worry as they have no telling evidence to indicate when the next one could be. The next earthquake could happen tomorrow or in another thousand years.
What worries geologists, seismologists, and local authorities in US west coast cities – San Francisco, Portland, & Seattle to name a few, more than anything else is the similarities between the faults located in Christchurch, NZ, and those faults located in the above mentioned US west coast cities. The faults in Christchurch were the source of a powerful 6.2 quake that struck the region on February 11, 2011, which killed at least 92 people and and caused extensive damage – even to modern buildings that were constructed to updated seismic standards. Christchurch Earthquake Photos.
The February 2011 quake was actually the second seismic event to hit Christchurch in less than a year. A more powerful magnitude 7.1 quake struck the same region in September of 2010. The big differences between the two events was that the latter quake was a much shallower quake, was centrally located under Christchurch, and occurred during the middle of the day – lunch time, when there were more people out and about and more exposed to falling debris. Being shallower, the intensity of the shaking was greater, and more damaging that the former quake. Ironically, the fault that created both quakes hadn’t even been discovered prior to the September quake. One such similar fault to the newly discovered Christchurch fault is the Portland Hills fault.
Portland, like Christchurch, has large areas of development built on water saturated sediment, which is susceptible to a phenomena known as, ‘liquifaction’, where the soil takes on the characteristics of a liquid. With no solid soil to sustain their weight, many buildings may be compromised and collapse from the loss of solid footing. The Guild’s Lake area is a perfect example of this. Now known as the Northwest Industrial district, the area was originally swamp land, but over time through the late 19th century and in to the 20th century, the lake area will filled in with dirt, sand, rocks, and river dredgings and was eventually developed in to the industrial area it is now, home to a major rail yard, numerous manufacturing facilities, and a sizeable petroleum storage and distribution facility. In a publication from Oregon State University’s News And Research Communications, Robert Yeats, Professor Emeritus from Oregon State University says, “Much of the Willamette Valley in Oregon is a prime example of soils that could liquefy, old sediments deposited during the floods and coming down from the Cascade Range.” This includes many of the areas around Portland, including the NW Industrial district.
Like in Christchurch, the Portland Hills fault would shake for a matter of seconds, not minutes like a tectonic plate quake. However, due to the relative shallow depths of the fault, the shaking in Portland would most likely be much more aggressive in nature. In addition, the Portland Hills fault runs, literally, straight through the heart of downtown Portland. Being as shallow as it is, the Portland Hills Fault is capable of significant damage. Regardless of whether a tectonic plate action hits or a strike-slip event, many of Portland’s aging buildings are not up to the task of standing up to an earthquake of any substantial magnitude.
Says Yeats, “It’s very similar in that sense to the area around Christchurch, which sits on sand, silt and gravel from the Southern Alps to the west. This issue, along with the risks posed by crustal faults, has to be considered in our building codes.” Many of the structures throughout the Portland area were constructed prior to any consideration of seismic reinforcement. Some of have been seismically retrofitted, but due to cost, inconvenience, and other factors, many have not. As we learn more about the faults in and around the Portland area, the local governments continuously review and update building codes and seismic standards.
“The same characteristics that caused such destruction and so many deaths in Christchurch are similar to those facing Portland, Seattle, parts of the Bay Area and many other West Coast cities and towns,” Yeats said. “And it’s worth keeping in mind that New Zealand has some of the most progressive building codes in the world. They are better prepared for an earthquake like this than many U.S. cities would be.” While Portland has come a long way in updating building codes, we’re still miles away from being prepared on just about every other front. For instance, Japan is the most highly prepared country on the planet for earthquakes, and yet, even with all of that preparation, they still suffer greatly during seismic events. Don’t get me wrong – being prepared is the key to survivability. If they were not as prepared as they are, the outcome of each quake would have been considerably more devastating. Cities like Portland and Seattle are no where near to being as prepared as those located in Japan or New Zealand. The likelihood of immense destruction is considerable.
One of the advantages places like Japan and New Zealand have over the Pacific Northwest, is the luxury of time. They have had decades longer to design building to withstand certain types of quakes, develop emergency plans and teach residents about the dangers of earthquakes and the proper actions to take during and after an earthquake. In Japan, students from a very early age are taught what to do. In fact, seismic activity in Japan is such a major portion of their everyday lives, schools drill for earthquake readiness on a monthly basis. New Zealand is developing and implementing similar programs into their school systems. Teaching children at a young age how to react to an earthquake, may help them be more proactive and confident and less frightened during an earthquake, and during the immediate time following one. Spending the time and money to give the understanding of being proactive and preparing ahead of time, will hopefully help increase the survival rate and reduce the need for dire reactions after-the-fact.
Regardless of whether you’re in Christchurch or Portland, being psychologically prepared is as important as being physically prepared – in that, I mean, having the knowledge that you have done (most) everything you can to be prepared before a quake may help take away the anxiety of the unknown. That knowledge should help you through the tough psychological grinder that is awaiting after the fact: Having a plan in place that everyone in your family is up-to-date on. Having enough food and water. Having prescription medicine set aside. Having shoes, flashlights, a way to cook food or sanitize water, something to wash with, or a place to use as a latrine. Having a survival kit in your car and in your home. Having an emergency kit at work. Being able to defend yourself and your family. Knowing where your rally points are and making sure everyone in your family knows where to go. Having enough readiness in place to give yourself a sense of peace of mind.
Part of surviving an earthquake, has to be assumed as luck. Are you in a place where your more likely to survive? At home? At work? Walking down the street? In your car? If we had the knowledge of when and where a quake was going to strike, we’d all either leave or be where we know we’d be safest. Unfortunately, earth does not give us that luxury. Being prepared gives us as much of that unavailable luxury as we’re going to get. And that is solely dependent on how much effort we are willing to put into our own survivability.
It is easy to become complacent about being prepared for an earthquake. The out-of-site-out-of-mind mindset. It is a fine line to tow; do you push the fear aspect of a potential pending earthquake, striking terror into the citizenry to the point of being apathetic, or do you use the subtle subliminal messaging, and hope to get the message across. The crux of it is, getting the majority of people to be prepared. The more prepared you are, the better chance of surviving a quake, and more importantly, surviving the two to four weeks after a quake strikes. Learning what we can from past events – like that in Christchurch, may help us be better prepared ourselves.
References:
http://www.oregongeology.org/sub/earthquakes/PortHillsFault.htm
http://www.oregonlive.com/environment/index.ssf/2011/02/comparing_portlands_quake_risk.html
https://www.portlandoregon.gov/pbem/article/394641
http://www.wou.edu/las/physci/taylor/g473/seismic_hazards/wong_etal_2001_pdx_hills_fault.pdf
http://oregonstate.edu/ua/ncs/archives/2011/feb/new-zealand-earthquake-damage-illustrates-risks-posed-shallow-crustal-faults
http://www.telegraph.co.uk/news/worldnews/asia/japan/8375591/Japan-earthquake-country-better-prepared-than-anyone-for-quakes-and-tsunamis.html