If you lived in Western Washington in 2001, you probably remember the Nisqually Earthquake. The powerful 6.8 magnitude earthquake caused over 400 injuries, and more than $4 Billion in damages in both Washington and Oregon. However, the Nisqually Earthquake is far from the worst-case scenario for Washington state.
What Exactly Is An Earthquake?
Washington State Emergency Management Division’s Earthquake and Volcano Program Coordinator, Brian Terbush explains that “An earthquake is that sudden release of energy from when two parts of the Earth’s suddenly slip past one another. The shaking that you feel is that energy, moving away from that sudden movement. The larger the amount of slipping, particularly the larger the surface area that slips, the stronger the earthquake is.”
“This is [similar] to a rubber band being stretched and stretched, and then eventually it breaks and rebounds,” said Corina Forson, Chief Hazards Geologist for Washington Geological Society. “This release of energy sends seismic waves traveling through the earth, and as those reach the surface, they cause the ground to shake.”
Faults Impacting Auburn
There are two faults that could cause damage in the Auburn area from being so close. The Seattle Fault runs roughly east-west right under I-90 from Bainbridge Island to Bellevue. The Tacoma Fault is [approximately] parallel to the Seattle Fault and runs south of Auburn. Additionally, a Magnitude 9 or greater Earthquake from the 700-mile long Cascadia Subduction Zone off the coast is strong enough, that despite being far away, would still cause “Severe Shaking.” This is a level strong enough to make walking difficult. The Seattle or Tacoma Faults would cause more intense shaking, being much closer to Auburn, but for a shorter time.
It is also important to remember that aftershocks may occur after an earthquake, and they have the same hazards as the main shock.
The Intensity of an Earthquake
An earthquake’s Magnitude rating measures the energy released at the source of the quake. The Modified Mercalli Intensity (MMI) rating measures the effect the earthquake had on the earth’s surface.
How strongly an earthquake is felt depends on two things. How close you are to the actual source of the earthquake (Hypocenter) and the type of ground beneath you. “[An earthquake’s] magnitude is like the wattage of a lightbulb,” said Terbush. “There is only one for the quake, and you will experience it differently based on how far away you are. If you’re right next to a 40-Watt lightbulb, it’s going to be very bright, and you might even feel heat. If you’re far away, it might not do much to light the part of the room you’re in. Also, that same 40-Watt bulb will seem much more intense if you’re in the dark than if you’re in a room that is already bright. The softer the ground you are on, the more intensely shaking.”
The Washington Department of Natural Resource provides earthquake scenarios on the Washington Geologic Information Portal. This portal displays a plethora of information, including the MMI for probable earthquakes. The portal projects that in Auburn, a Magnitude 9.0 earthquake from the Cascadia Subduction Zone will have a 7.5 MMI rating. This rating is “very strong: Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.”
Projections for a Seattle 7.2 was also in the 7.5-8 range. A Tacoma 7.1 earthquake is listed at an MMI 8 rating. This is “severe: Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.”
The PSNS estimates that there is about an 84% chance we’ll experience a damaging earthquake within the next 50 years.
Want more on Earthquakes? Check out our supplemental article Earthquakes: A deep dive
Hazard Caused by Earthquakes:
The Pacific Northwest Seismic Network (PNSN) states that “while they are often used as synonyms, it is useful to distinguish between “hazards” and “risk”. Hazards are the natural phenomena that might impact a region, regardless of whether there is anyone around to experience them or not. Risk refers to what we stand to lose when the hazard occurs; it is what we have built that’s threatened. Risk can be usually be measured in dollars or fatalities, Hazard is generally measured in more physical units: energy, shaking strength, depth of water inundation, etc.”
Risk of Damage to Infrastructure:
“Any unreinforced masonry buildings are at risk, which includes many older buildings throughout the region, not just Auburn,” said City of Auburn Emergency Manager Jerry Thorson. “I was in a fire station in Federal Way when it hit, [During the Nisqually Earthquake]. The 20 seconds it lasted seemed like a very long time while under my desk! Auburn was hit similar to the region. Damage was fairly minor, and I’m not aware of any remaining damage. People shouldn’t expect that minor impact from future quakes.”
Electrical lines and telephones may fall from the shaking. Gas lines might be ruptured by shaking or possibly by some of the secondary impacts of earthquakes, such as landslides, or liquefaction. Fire is a risk in places where these two things come together (i.e., sparks from damaged electrical systems and ruptured gas lines).
Damage to roads and bridges and landslides may make routes impassable. Gas stations and critical infrastructure may struggle to resupply because of this.
An important thing to remember is that aftershocks are likely to cause additional damage or further harm things damaged in the original earthquake. “Maybe the first earthquake only weakened the parapets of an unreinforced masonry building: an aftershock could cause it to fall,” said Terbush.
Environmental Hazards After an Earthquake
Earthquakes can cause several environmental hazards. According to the PNSN, “earthquake hazards include any physical phenomenon associated with an earthquake that may produce adverse effects on human activities.”
The PNSN lists the primary earthquake hazards as ground shaking, landslides, liquefaction and surface rupture. “Secondary earthquake hazards are those that are caused by the primary hazards and may often be more catastrophic.” Continues the PNSN website. The secondary hazards listed are, “tsunami, seiche, flooding, and fire.”
Many factors affect the damage and impact an earthquake will have, Auburn is most likely to see significant ground shaking, and landslides explained Thorson, “The entire valley floor is considered a liquefaction area, that includes over 60% of our structures.”
Liquefaction
Liquefaction happens as a result of a water-saturated, granular (sandy) soil loses strength during the type of shaking created by an earthquake. “One easy way to think about it is when you go to the beach. You can walk on the wet seemingly hard sand, but when you stop and wiggle, your feet the sand liquefies and moves around your feet and eventually covers them with sand. This is (sort of) what could happen in some highly liquefiable areas if the shaking is strong enough and lasts a long time,” said Forson.
Landslides
Landslides are like liquefaction. Some areas, such as over-steepened cliffs, saturated soils, loose sediment, can already be susceptible to landslides. When strong shaking occurs, such as produced with an earthquake, it can trigger landslides.
Tsunamis
“It’s really unlikely that a tsunami would reach as far upstream as Auburn,” Terbush continued. “Still, since people travel, to the coast, to the Sound, or even other tsunami-prone areas around the world, it’s important to understand the warning signs of tsunamis. If you feel strong an earthquake shaking and you’re near the coast: drop, cover, and hold on until the shaking ends, then get to high ground as quickly as possible.”
If there ever were a tsunami coming into Auburn, use the already marked Lahar evacuation routes to get away from the river, and to higher ground.
What To Do During An Earthquake
Thorson reminded, “The best method to react is still “Drop Cover and Hold.” Trying to quickly exit a building places one at risk of falling and injuring yourself. [It also] places people at significant risk of injuries from falling objects. There are many good images that show bricks and other structural elements on the sidewalks outside of the building. If someone was trying to escape when that came down, it could easily be fatal.”
If you are driving when an earthquake occurs, “safely pull to the side of the road and stop the car. If possible, remain in the car until the shaking stops,” said Thorson. “I was talking with someone a while back that was driving during the Nisqually earthquake and thought he had a flat tire at first. Then he saw the wires on some telephone poles shaking and knew it wasn’t a flat.”
Students in school should follow the same “drop, cover and hold” method. “And follow their teacher’s directions. I do have to give the Auburn School district a shout out, they’ve been working really hard on emergency preparedness and have made some good progress in the last couple of years,” commended Thorson.
Predicting Earthquakes
Even with as much scientific research, and constant monitoring that there is – there is still no manner to predict earthquakes. “Unfortunately, the most warning we will be able to get is seconds, to tens of seconds with the Earthquake Early Warning system being developed on the West Coast. Besides that, at least based on our current understanding of earthquakes and earth movements, we cannot predict earthquakes,” said Terbush. “What we can do, is understand that they are a hazard in this area, that will have huge consequences when they occur someday. Knowing this is the first step. Understanding that you are capable of taking actions to prepare your home, your workplace, yourself, and your family for it is the next step.”
Currently in development is the ShakeAlert Early Earthquake Warning System. The USGS is presently seeking pilot users. “The USGS has been developing this technology for over ten years now with the help of State and University Partners in California, Oregon, and Washington, and Collaborating with British Columbia, basing the idea most off of the system in place in Japan,” said Terbush.
The BIG ONE
While there is no known way to predict earthquakes, scientists can “look at the geologic record and see what we can learn about how often earthquakes have happened in the past and what that may tell us about when they may happen in the future. The last big M9 Cascadia earthquake happened in 1700,” explained Forson.
The PNSN states that “the last known megathrust earthquake in the northwest was [January 26th] 1700. Geological evidence indicates that such great earthquakes have occurred at least seven times in the last 3,500 years, a return interval of 400 to 600 years.”
Forson continued saying that, “smaller earthquakes (magnitude 8 or so) happen more frequently than larger magnitude 9 events. [I understand Cascadia subduction zone] earthquakes happen every 200-1000 years (depending on the earthquake size). So, based on that time interval, and that we know the last big one happened 318 years ago we are “in the window” for another big one to happen.”
According to the PNSN, there is a 10-20% chance there will be a Cascadia Subduction Zone Earthquake within the next 50 years.
Comparing the Pacific Northwest To Japan
It is common to see Japan’s 2011 Tohoku earthquake as a reference for what the Pacific Northwest should expect.
However, Forson warns that we should be cautious in the comparison. “One big takeaway is that, in my opinion, Japan was far more prepared that we are in the Pacific Northwest, and they still suffered major tragedy,” said Forson. “If we want to have limited fatalities and minimize economic losses we need to prepare at an individual level and as a state. This requires hard mitigation, such as seismically upgrading critical facilities (schools, police stations, hospitals, etc.), critical infrastructure (bridges, roads, power supplies, etc.), building redundant communication, and building vertical evacuation options for coastal residents.”
“It also means better understanding our geologic hazards,” Forson continued. “Completing tsunami hazard mapping for the state, studying active faults, understanding earthquake recurrence, etc. and limiting development in geologically hazardous areas.”
How To Prepare
Individual and family preparedness is critical to the survival of a natural disaster. While ‘The Big One’ may not happen in our lifetime, Forson feels it is better to be safe than sorry. “I liken it to getting in a car. You hope that you won’t get in a crash, but you wear your seatbelt so that if you do, you will be safer. Preparing now could save you and your loved ones when disaster strikes. Make go bags for your car, your house, your work and talk to your family about your emergency plan and PRACTICE it.”
Ready.gov’s Resource Page To Help Plan Head
“We at the state recommend that realistically, everyone should stock two weeks’ worth of supplies,” said Terbush. “Food, water (1 gallon, per person, per day), comfort items, and other needs. This isn’t an insurmountable task, and anyone can do it. Take it a little bit at a time and try to stock an extra bit of non-perishable food every time they go to the grocery store.”
“I keep gloves and a few tools in [my kit] in case I need to help with any rescues in our neighborhood,” said Thorson. He also recommended “tools to shut off the natural gas and water if they’re leaking. It’s also important to have a battery-powered radio to listen to warnings and information on shelters, evacuations, etc. Signing up for emergency alerts on email and phones is also important.”
Terbush also addressed homeowner preparedness, “homeowners can also [prepare their homes]. [Securely bolting] your house to its foundation can mean the difference between it sliding off the foundation during shaking, which will make it immediately unsafe, and only requiring minimal repairs. Secure your water heaters to the wall to make sure they don’t tip over during shaking. [Doing] this means less damage, and the water in your water heater can also be collected immediately following an earthquake as extra water that you have available.”
Homeowners can utilize the FEMA Home Hazard Hunt to help prepare their home. Download it here.
How being CERT Trained Can Help after an Earthquake
Thorson explains that “the CERT class teaches many skills that will be very helpful after an earthquake. We teach personal preparedness, light search and rescue techniques, basic first aid, how to work as part of a team and many other [vital] skills. Anyone that takes the class will be in a much better position to deal with an earthquake, flood, or [other emergencies].
Here is the current 2019 CERT class schedule. The next CERT class begins on April 16th.
Be Prepared, Not Worried
“Understanding the hazard is the first step. Scientists, emergency managers, and other professionals have provided the tools. You need to judge the level of hazard you might face. Now take that knowledge, and do something with it,” said Terbush. “A huge event like a megathrust earthquake will drastically change life as you know it. It could occur several seconds from now, or it may not occur within our lifetimes. [However,] the next time Snowpocalypse, a major flooding event, a fire, or windstorm hits, you, your family and loved ones will already be prepared for varying degrees of damage, and you won’t be rushing to a store with empty shelves.”
“Despite these hazards,” Terbush reminded, “[the Pacific Northwest] is a beautiful and great place to live. So, you could move, or stay here, and be prepared. It’s the same as anywhere else.”
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