Major Pacific Northwest earthquake could trigger another along West Coast

"The Big One" could trigger larger earthquake along West Coast

Most of us have probably heard that when it comes to earthquakes, "The Big One" could happen at any time, but a new study has now found that if the "big one" happens in the Pacific Northwest, it could trigger an even bigger one and affect cities up and down the West Coast.

SEATTLE - Most of us have probably heard that when it comes to earthquakes, "The Big One" could happen at any time, but a new study has now found that if the "big one" happens in the Pacific Northwest, it could trigger an even bigger one and affect cities up and down the West Coast.

The backstory:

In 2001, the 6.8 magnitude Nisqually earthquake toppled parts of buildings, left 400 people hurt and caused billions of dollars in widespread damage. That earthquake serves as a stark reminder that another earthquake like this, perhaps bigger, is still looming. 

"This is essentially a certainty, and how we respond to it is the only part that's uncertain," said Dr. Chris Goldfinger, geologist and the lead author and principal investigator of a 2025 study.

What they're saying:

That study found if a major earthquake happened on the Cascadia subduction zone, that would trigger San Andreas Fault to go off a short time later.

"We discovered that the earthquake deposits near where the two faults meet at Cape Mendocino were stacked basically directly on top of each other, with apparently no intervening time passing between the two events," Goldfinger said.

He shared a video with FOX 13 showing the sequence of Cascadia earthquakes from the past 10,000 years. It also shows San Andreas earthquakes going off. He told FOX 13, it’s not a matter of if a big one will happen, but when.

So, what is considered a big earthquake?

"If you want to think of it as t-shirt sizes, from extra-large, which might be a 9.1 or 9.2 is where we think the maximum is, down to magnitude-7 earthquakes," Goldfinger said. 

He explained those earthquakes would affect Seattle, Portland, Vancouver, and San Francisco, cities up and down the coast.

Local perspective:

These findings come as the Great Shakeout happens on Thursday, October 16. It’s a time when millions of people worldwide practice earthquake drills at work, school and home.

Despite drills like these, Goldfinger says we’re still not prepared because many of these areas were built on top of ticking time bombs.

"We have very, very fragile infrastructure in most of our towns and cities," Goldfinger said. "So, we have a lot of unreinforced masonry buildings, lift-slab concrete buildings that pancake in an earthquake and things like that, and the progress to replacing those and retrofitting those is very, very slow, and, you know, this is a long term, expensive process."

In the meantime, he told FOX 13 that there are some things people can do now to get their home earthquake ready. For example, if you have a gas hot water heater, he said make sure those are strapped down so they don’t tip over and break a gas line, which could start a fire during an earthquake. 

"Go around your house and start thinking about ‘what would my house be like in an earthquake?’" Goldfinger said. He also recommends surveying tall, heavy items in your home that could tip over, and make sure your home is bolted to the foundation, because there are a lot of older homes that are not.

"You don't want your house to slide off of the foundation during the earthquake, that’s going to total it probably," he said.

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