Earthquake
The Cascadia Subduction Zone runs 600 miles from northern California to British Columbia. It has been building pressure for over 300 years. Here's what that means for you — and what to do about it.
The first fifteen minutes
David is working from home in his 1940s bungalow in Fremont, north of the Ship Canal. It's 11:47 on a Wednesday morning. He's at his desk by the window that looks out at the neighbor's Douglas fir. The first thing he notices isn't the shaking — it's the sound.
A low groan, structural, coming from the house itself. Then the floor drops — not much, maybe an inch — and comes back up, and now everything is moving. The monitor slides. His coffee goes over. The bookshelf sways and he's under the desk before he makes the decision to get under the desk, which is exactly what he practiced.
The shaking lasts somewhere between one minute and four. He'll never be sure. It stops in stages — the violent lateral movement first, then a residual rocking, then stillness that doesn't feel like stillness because his inner ear hasn't caught up.
The power is out. He knows this because the hum he never notices is gone. His phone has no signal — the cell towers are either down or overwhelmed. From outside, car alarms. From somewhere east, what sounds like it might be a building collapse, or might be a shipping container falling at the port. He can't tell.
David has a plan. He goes to the kitchen and turns off the gas at the valve behind the stove — a quarter turn, the wrench is in the drawer, he practiced this too. He checks the chimney from inside: the unreinforced brick chimney that he's been meaning to retrofit for three years. There's a crack at the roofline. Mortar dust on the mantel. It held. Barely.
His partner Jun is on the 14th floor of a retrofitted office building downtown. Their plan is simple: if phones don't work, Jun walks north. David stays put unless the house is unsafe. They meet at Gasworks Park. If neither can get there, there's a handwritten note on the fridge with the backup plan and the out-of-area contact who will relay messages.
David opens the tap. Nothing comes out. The water main serving his block runs under Aurora Avenue through fill soil from the 1917 Fremont regrading. Fill soil liquefies in major earthquakes. He expected this. Under the stairs: three gallons of stored water, plus two cases of bottled water he rotates every six months. It's enough for three days for two people. He thinks it should be more. He's right.
It's been eight minutes since the shaking stopped. David puts on hard-soled shoes — there's broken glass he can hear crunching in the kitchen. He walks next door to check on the Nguyens. Their chimney didn't hold.
What's happening under the ground
The Cascadia Subduction Zone
Off the coast of the Pacific Northwest, the Juan de Fuca tectonic plate is sliding beneath the North American plate at roughly 40 millimeters per year. This boundary — the Cascadia Subduction Zone — stretches from Cape Mendocino in northern California to Vancouver Island in British Columbia.
Subduction zones produce the largest earthquakes on Earth. The last full rupture of the Cascadia zone happened on January 26, 1700, at approximately 9 PM local time. We know the date because the resulting tsunami crossed the Pacific and was recorded in Japanese coastal villages. The earthquake was estimated at magnitude 9.0.
That was 326 years ago. The average interval between full-margin ruptures is approximately 243 years, based on turbidite records — layers of disturbed sediment in ocean cores. We are past the average. This does not mean an earthquake is imminent. It means the probability is not small.
What "magnitude 9.0" actually means
The Richter scale is logarithmic. A magnitude 9.0 earthquake releases roughly 1,000 times more energy than a magnitude 7.0. The 2001 Nisqually earthquake that cracked buildings in Olympia and Seattle was magnitude 6.8. A full Cascadia rupture would release about 11,000 times more energy than Nisqually. The shaking would last 3-5 minutes — not the 45 seconds of Nisqually.
Why it matters where you are
Not all ground shakes the same way. Seattle, Portland, Vancouver, and many other Cascadia cities are built partially on fill soil, river deltas, and reclaimed tideflats. These soft soils amplify seismic waves — a phenomenon called liquefaction. The same earthquake that rattles a house on bedrock in the Cascades can collapse one built on fill in the Duwamish Valley.
Your risk depends on three things: distance from the fault, the soil under your building, and the construction of the building itself. A modern wood-frame house on firm soil is among the safest structures in an earthquake. An unreinforced masonry building on fill is among the most dangerous.
Your state or provincial geological survey provides liquefaction susceptibility maps — search for your area's geological hazards portal (in Washington, check the WA DNR Geology Portal; in Oregon, the DOGAMI HazVu; in BC, the Natural Resources Canada hazard tools). If you don't know what kind of soil your home sits on, this is worth checking.
The coastal timeline
If you live on the Washington, Oregon, or BC coast, there is an additional concern: tsunami. After a full Cascadia rupture, the first wave could reach the outer coast in 15-20 minutes. For some low-lying coastal communities, that's the entire window. Tsunami evacuation routes are posted in most coastal towns. If you live or vacation on the coast, know your route — and know that the shaking itself is your warning. If it's strong enough that you can't stand, get to high ground immediately. Don't wait for an official alert.
What to do
Before, during, and after
Before the earthquake
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Know your building
Is your home wood-frame (good — flexible) or unreinforced masonry (dangerous — brittle)? Is the foundation bolted to the sill plate? If you own a pre-1970 house, a seismic retrofit ($3,000-$7,000) is one of the most impactful things you can do. Ask your city's building department about retrofit programs — some offer subsidies.
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Make a household plan
Where do you shelter during shaking? (Under a sturdy desk or table, away from windows and chimneys.) Where do you meet if phones don't work? Pick two locations — one near your home, one farther away. Choose an out-of-area contact who can relay messages — local cell networks get overwhelmed fast, but texts to someone outside the affected area often get through when voice calls don't.
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Secure what falls
Strap your water heater to the wall. Secure tall bookshelves. Move heavy objects off high shelves. In a major earthquake, unsecured furniture and appliances are responsible for most injuries inside homes.
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Know your gas shutoff
If your home uses natural gas, learn where the shutoff valve is and keep a wrench nearby. Practice the quarter-turn. After a major earthquake, gas leaks from broken lines are a serious fire risk. Only shut it off if you smell gas — and know that once you shut it off, only the gas company can turn it back on.
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Store water
One gallon per person per day, minimum three days. Seven days is better. Municipal water systems in the Puget Sound region depend on pipes that cross liquefiable soils. Restoration could take days to weeks. This is the single most important supply you can have.
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Build your kit
Water, first aid, medications, flashlight, radio, cash, copies of important documents, food that doesn't need cooking. A full checklist is in our build-your-kit guide.
During the shaking
Drop, Cover, Hold On
This works. It's not a cliché — it's the result of decades of research into what kills and injures people in earthquakes. Drop to the ground. Get under something sturdy. Hold on. Do not run outside — falling debris from the exterior of buildings is more dangerous than being inside a wood-frame structure. Do not stand in a doorway — that advice is outdated and wrong for modern construction.
If you're in bed, stay there. Cover your head with your pillow. If you're driving, pull over away from overpasses and bridges, and stay in the car. If you're on the coast and the shaking is strong enough that you can't stand, move to high ground as soon as the shaking stops. That's your tsunami warning.
After the shaking stops
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Check yourself and others
Injuries from falling objects and broken glass are common. Put on hard-soled shoes before moving through your home. Check on household members, then check on neighbors — especially elderly or disabled neighbors who may not be able to self-rescue.
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Check for gas leaks
Smell gas? Shut it off, open windows, leave the building. Don't flip light switches or use anything that could create a spark.
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Expect aftershocks
A magnitude 9.0 mainshock will produce thousands of aftershocks, some potentially in the magnitude 6-7 range. These can cause additional damage to weakened structures. Do not reenter a damaged building to retrieve supplies. Aftershocks come without warning.
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Use your plan
Go to your meeting point. Text your out-of-area relay. If you have a battery or hand-crank radio, turn it on — local authorities will broadcast instructions on NOAA weather frequencies and local AM stations.
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Conserve water
Do not flush toilets — sewer lines may be broken. Use your stored water for drinking and first aid first. Fill bathtubs and containers with any remaining tap water before the system drains completely.
What to have ready
Your earthquake supplies
You don't need to buy a pre-made kit. Most of what's on this list is at your local hardware store and pharmacy. Set aside a Saturday afternoon. For the full checklist with quantities and sourcing suggestions, see our build-your-kit guide.
The essentials, in order of priority:
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Critical
Water
One gallon per person per day, minimum 3 days. Municipal water will likely fail in areas with fill soil. Restoration takes days to weeks.
Grocery store, or fill your own food-grade containers from the tap. Rotate every 6 months.
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Critical
First aid kit
Cuts from broken glass are the most common earthquake injury. Include gauze, bandages, antiseptic, medical tape, tweezers, scissors.
Any pharmacy. Pre-made kits work fine.
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Critical
Medications
If anyone in your household depends on daily medication, keep a 7-day supply in your kit. Pharmacies may be closed or inaccessible.
Ask your doctor for an extra prescription for your emergency supply.
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Important
Flashlight and batteries
Power outages may last days. You need light to assess damage, find supplies, and move safely through broken glass.
Hardware store. Keep one by your bed too.
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Important
Battery or hand-crank radio
Cell service will be overwhelmed. NOAA weather radio and local AM stations will be your primary information source.
Hardware store or online. NOAA weather radio with SAME alert is ideal.
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Important
Cash in small bills
ATMs and card readers require power and network. Cash works when nothing else does. Keep $200 in small bills.
Your bank. Store in a waterproof bag with your kit.
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Important
Copies of important documents
Insurance policies, IDs, medical records, emergency contacts. If your home is damaged, you need these to be accessible.
Photocopy or photograph. Store in a waterproof bag with your kit, and keep a digital copy in cloud storage.
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Recommended
Wrench for gas shutoff
A crescent wrench or dedicated gas shutoff wrench, stored near the meter. Practice the quarter-turn before you need it.
Hardware store. Some utility companies offer free shutoff wrenches.
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Recommended
Non-perishable food (3-7 days)
Canned goods, dried fruit, peanut butter, crackers. Nothing that requires cooking — your stove may not work and you shouldn't use gas appliances if there's any risk of a leak.
Grocery store. Include a manual can opener.
What David did right
By 12:30, David has checked on three neighbors and helped the Nguyens clear the chimney bricks that fell onto their porch. His stored water is under the stairs, the gas is off, and the handwritten note is on the fridge where Jun will find it if David isn't home when Jun arrives.
Jun walks north from downtown. It takes two hours — the Fremont Bridge is closed for inspection, so Jun crosses at the Ballard locks. They meet at Gasworks Park at 2:15 PM. Neither has cell service. Both knew where to go.
David's house has a cracked chimney and a broken kitchen window. The foundation, bolted to the sill plate three years ago, held. The water heater, strapped to the wall, didn't fall. The stored water, the first aid kit, the flashlight, the battery radio, the cash in small bills — all of it in the plastic bin under the stairs, all of it exactly where he put it.
None of this is heroic. David isn't a survivalist. He's a person who spent a Saturday afternoon thinking about what could happen and doing something about it. That Saturday afternoon is the difference between David helping the Nguyens and the Nguyens helping David.
You can be David. A hardware store, a pharmacy, a Saturday, and a plan. That's all it takes.