What are the most dangerous fault lines for Seattle? And when are they going to erupt?

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Seattle is overdue for a big earthquake. But which fault lines is going to erupt first? The Cascadia Subduction Zone, the Seattle fault of the South Whidbey Island Fault

The western half of Washington state is considered earthquake country, with the potential for very large quakes.

Discover in this article the most dangerous earthquake zones for Seattle and its area: The Cascadia Subduction Zone, the Seattle Fault and the South Whidbey Island Fault.

The below map shows that Seattle and its surroundings is constantly being rattled by small earthquakes and tremors.

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Seattle is an earthquake prone area. What are the major fault lines in the region? Earthquake map via My Northwest

On Dec. 15th, a small swarm even hit near Bremerton, a few miles away from downtown.

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Earthquake swarm hits Seattle on december 15, 2020. Earthquake map via My Northwest

While the intensity of this seismic event has now decreased, a big earthquake is overdue in the region. So I think it is worth your time to learn more about the biggest seismic riskss and major fault lines criss-crossing this part of the Pacific Northwest, namely:

  • The Cascadia Subduction Zone running roughly parallel to the Pacific Coast from northern California past the northern tip of Canada’s Vancouver Island.
  • The Seattle Fault, which runs east to west just south of downtown Seattle. It ends up near the Cascade Mountains and west onto the Olympic Peninsula.
  • The South Whidbey Island Fault running from northwest to southeast of the southern tip of the island.

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The most dangerous earthquake faults for Seattle: The Cascadia subduction Zone, the Seattle Fault and the South Whidbey Island Fault.

Now let’s visit the 3 most dangerous earthquake faults for Seattle one by one:

1. Cascadia Subduction Zone

The Cascadia Subduction Zone is a giant fault running from Cape Mendocino, Calif. past Oregon and Washington and doesn’t end until it’s north of Vancouver Island in Canada.

You saw its potential in the 9.1 magnitude Tohuku earthquake and tsunami that hit northeastern Japan in March 2011. Tohoku killed nearly 16,000 people; most died as a result of drowning or being crushed in the tsunami.

Because Japan was so well prepared, most retrofitted buildings outside of the tsunami zone survived. This part of the Japanese coast had not seen this type of seismic rupture in some 800 years, and what failed was that walls built to keep tsunami waves were not high enough.

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The Cascadia Subduction Zone poses a major earthquake threat for Seattle area. Shaking map by Department of Natural Resources

In Washington, we do not have tsunami walls. Along the coast residents may have between 20 and 30 minutes to get to higher ground.

The Westport area is now the first in North America to have a community vertical evacuation structure, a building strong enough to resist earthquake and tsunami wave forces and give people a platform above the expected wave heights. That place is the Ocosta School.

But the Cascadia Subduction Zone isn’t just a fault; it’s an overlapping joint between tectonic plates, parts of the Earth’s crust that float on layers of molten rock.

There’s a reason the lands around the Pacific Ocean are called the “Ring of Fire.” The earthquakes, tsunamis, and the proximity of volcanos are all part of the same system.

The coast is now the home of one of the state’s largest network of warning sirens called All Hazard Alert Broadcast (AHABs). But Forson says you also need to know what to do when the shaking happens.

There are also tsunami evacuation signs on the highways. Westport currently is the only location with a vertical evacuation structure designed for a tsunami.

We do not encourage people to evacuate in vehicles. We’re working on pedestrian evacuation maps that show the best routes for pedestrians to take to evacuate,” said Forson. “You just need one person to crash or a power line to fall over the road, and the roads are unusable.

That’s why we’re pushing for a lot of vertical evacuation structures to be built – hotels or schools, because it’s not an easy problem to solve,” he said.

Resources on tsunami danger and preparedness in Westport, Grays Harbor County, Long Beach Peninsula, and Coastal evacuation maps.

2. Seattle Fault

Moving inland, the Seattle Fault is capable of a magnitude 7.

That may not sound like much more than the magnitude 6.8 quake of 2001 based on the numbers, but that the Nisqually quake occurred some 30 miles underground.

Then consider that the Seattle Fault is a complex of faults with various branches that run at or just below the surface.

The risk is complicated, but there are millions of people who live in the Seattle area,” said Forson. “What we know about this fault is that it’s ruptured may times in the past…it will happen again. We just don’t know when.

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The Seattle Fault zone runs throught the city of Seattle and represents a major threat for its ihnabitants. Map by Department of Natural Resources.

Across the northern portion of Bainbridge Island, light radar or lidar images taken from airplanes clearly show the Seattle Fault running right on the surface.

Another piece can be seen under the elevated lanes of northbound Interstate 5 in South Seattle not far from the Rainier brewery.

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The Seattle Fault is a very shallow earthquake fault line. The Seattle Fault on Bainbridge Island (left); an aerial image of Bainbridge Island (right).

The Seattle Fault is also likely to create a tsunami that would inundate Harbor Island and much of SODO, Interbay, and the waterfront. It could also create dangerous currents and hazards to the north including Everett.

What scientists don’t know is its timing interval.The last time was 1,000 years ago between 900 and 903 A.D.,” said Forson. “It will happen; we don’t know when.

What about the localized tsunami risk? In the 1990’s, scientists produced an animation that shows inundation, and people won’t have much time to run to higher ground. In some areas getting up a hill to higher ground will be difficult. Some people in places like SODO and Harbor Island may have to flee to higher floors in a building.

You can look at different geological hazard maps on the website of the Department of Natural Resources.

3. South Whidbey Island Fault

The South Whidbey Island Fault is also dangerous.

It’s significantly larger than the Seattle Fault, and South Whidbey could hand us a magnitude 7.5 earthquake.

That could spell trouble not only for its namesake island but for south and north King County and further west.

The crustal faults – the Seattle Fault, the South Whidbey Island Fault, the Tacoma Fault – those are less well known,” said Forson.

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The Southern Whidbay Island Fault represents another major earthquake threat for Seattle and its residents. Map by

And while scientists keep digging for more information and more situational awareness of what we face, the other problem is human.

A lot of people are transplants,” Forson said. “They didn’t grow up here, they haven’t heard this story. So they don’t necessarily know the threats they face.

Earthquakes. Volcanic eruptions. Devastating wind storms. Floods. Mudslides. Why is Strange Sounds focusing so much on disaster preps? It’s certainly not to scare you. Emergency planners all had a simple message: It’s not IF a disaster will happen, it’s WHEN.

The experts say few are ready. And being ready means being able to support yourself, your loved ones, your neighborhood for 2 weeks. Because after a region-wide event, it could take that long for help to come from the rest of the country and world.

Seismologists estimate that such quakes and tsunami waves occur roughly every 500 years on average on the Cascadia Subduction Zone. There’s approximately a 14% chance of another approximately M9 earthquake occurring in the next 50 years.

There’s a must-see documentary film called ‘Cascadia The Big One’ that exposes what’s currently going on in this region of the Cascade volcanoes and the Pacific NorthWest.

Learning earthquake faults around where we live is a first good way to prepare the next devastating earthquake. Be prepared and read more on DNR, USGS, King5, Strange Sounds and Steve Quayle.

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  1. People are already fighting over toilet paper, just imagine what will it be like when they go shopping for food and the shelves are almost empty. A half dozen people reaching for the last can of soup, someone could lose their life over that.

    Earthquakes, tornadoes, hurricanes, pandemics, too many people think it can’t happen to them and they still think that they can still make a quick run to Walmart to pick up enough to last for 2-3 days and then the govt. and the Red Cross will be there to care for them.

    America is going to pay for sitting back doing nothing while almost 70 million babies were slaughtered and their body parts sold to the highest bidder for the last 43 years. Still think we’ll avoid God’s wrath, it’s not going to happen regardless of what the multi millionaire TV preachers tell you. America is going to be punished just like the rest of the world.

  2. Strabge sounds very good report thanks a lot. With Medical Martial Law imposed in Washington state. Part 2 will be full Martial Law and mandatory vaccines? We pray for people of WA and our all north Americans as well.
    Doctor reveals the horrors Italian medics are facing in ‘overwhelmed’ hospitals where dying patients are being left untreated – as experts warn UK and US are just two weeks behind Italy and the public are not SCARED enough

    An intensive care doctor in northern Italy has described the scale of the crisis
    The medic said colleagues were becoming ‘sick and emotionally overwhelmed’
    Also issued a warning for the UK that the Italian chaos could come to Britain
    Experts have warned that UK outbreak may be around two weeks behind Italy’s

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