Your phone blares, "Earthquake!" The voice instructs you to duck, cover, and hold on. About 30 seconds later, the shaking starts.
At first, it makes the furniture sway. It's stronger than the little quakes you normally get here in Seattle. Another 30 seconds later, the shaking suddenly intensifies.
Pictures fall from the walls, objects fly across the room, and the dining table you're sheltering under begins to scoot across the floor, several inches at a time.
A loud rumble fills the air. It's the sound of the city's buildings swaying and creaking and all their contents shimmying, wobbling, scraping across floors, or crashing down from shelves.
Seattle isn't even that close to the earthquake's epicenter.
The Olympic Mountains and about 100 miles stand between the city and the ocean. For people on the coast, the shaking is much worse.
"It will be the worst natural disaster our country has ever seen."
Robert Ezelle, director of emergency management at Washington state's Military Department
After about six minutes, the earthquake dies down, and a new countdown begins. People along the coast now have 10 to 30 minutes to reach high ground before a giant wave engulfs the Pacific Northwest.
Tsunami sirens wail in some towns. In others, the earthquake has knocked out alert systems.
From Northern California to Vancouver Island, a wall of water up to eight stories high surges onto the coast.
Over the next hour or two, the tsunami makes its way up rivers and straits and into Puget Sound. It's much smaller by the time it reaches Seattle, but it floods some streets.
Between the earthquake and the tsunami, 14,000 people died, many more were trapped or injured, and more than 618,000 buildings were damaged. The shaking triggered landslides, fires, and spills of hazardous materials.
But the disaster has just begun.
Eventually, the total economic losses will amount to $134 billion, placing it high among the costliest natural disasters in US history.
The scene above is a worst-case scenario of a megaquake striking the Pacific Northwest. Emergency managers have spent decades preparing for it. Still, they say the region isn't ready.
"To be fully, completely, and totally prepared is an impossibility," Robert Ezelle, the director of the emergency-management division of Washington state's Military Department, told Business Insider, "just because of the magnitude of the event."
Inside the major disaster brewing off the coast of the Pacific Northwest
About 100 miles offshore from the Pacific Northwest, deep beneath the seafloor, two tectonic plates are building tension that could erupt at any moment.
In a region called the Cascadia subduction zone, the Juan de Fuca oceanic plate is sliding (or "subducting") beneath the North American plate — but its edge is stuck. As the plate keeps pushing against its locked-up edge, stress builds.
"It's ominously quiet," Harold Tobin, Washington's state seismologist and the director of the Pacific Northwest Seismic Network, told BI. "The fact that it doesn't even produce little earthquakes to any significant extent makes us believe that it is completely locked up."
Scientists like Tobin fear that without releasing tension through smaller earthquakes, the Cascadia subduction zone is more likely to erupt in a "megathrust" earthquake — or megaquake for short — with a magnitude of about 9.
"It will be the worst natural disaster our country has ever seen," Ezelle said. That's why some call it the "Big One."
On average, the Cascadia subduction zone produces an immense earthquake every 200 to 500 years. The most recent one was in 1700.
Just how big is the Big One?
The Richter scale, which measures earthquake magnitude, is logarithmic, not linear. That means a magnitude 9 quake releases about 32 times as much energy as a magnitude 8 but about a million times as much as a magnitude 5.
The closest thing in human memory to the Big One occurred in Japan in 2011. That magnitude 9 event, called the Tohoku earthquake, also came from a subduction zone.
It generated a tsunami that reached 130 feet high, inundated over 1,200 miles of coastline, and washed thousands of people out to sea. Together, the quake and tsunami killed an estimated 18,500 people.
It's hard to imagine the power of a magnitude 9 quake, but the Seismic Sound Lab, a group of Columbia University scientists, created a video that tries to convey it through sound.
The animated video, below, shows every earthquake in Japan from 2008 through 2014, accompanied by sounds of various volumes. A normal background hum of magnitude 4, 5, and 6 quakes gives way to an intensely loud boom, the Tohoku event, about 22 seconds in. (The label saying the event occurred in 2012 is incorrect.)
For years after the Tohoku event, aftershocks rippled across Japan, adding to the damage, including a 7.1 earthquake in 2021.
Likewise, in the Pacific Northwest, aftershocks could continue for months, maybe even years, following the Big One. The first tsunami may not be the biggest.
The aftermath of the Big One
Scientists, Ezelle's department, and the Federal Emergency Management Agency have practiced for the Big One in two "Cascadia Rising" exercises, one in 2016 and another in 2022.
"People that we're counting on to be first responders may very well be victims."
They've found that in the days following the megaquake, much of western Oregon and Washington may be without electricity, internet, cell service, or drinking water.
In certain areas, it could be more than two weeks before help arrives because landslides, sinkholes, bridge collapses, and other damage to roads could make travel impossible.
Both Oregon and Washington advise that all residents have enough food, water, and medicine on hand to last at least two weeks.
"People that we're counting on to be first responders may very well be victims," Ezelle said. "A lot of it is going to be neighbors taking care of neighbors."
Among dozens of preparedness goals set after the last Cascadia Rising exercise, Ezelle's division is assessing the state's roadways to identify "lifelines" through the mountains — ways it might piece together surviving or quick-to-repair roads to transport critical supplies to the coast.
Once those lifelines open after a megaquake, national and international aid can step in. A FEMA spokesperson told BI in an email that the agency would have teams ready to step in "almost immediately."
Retrofitting old buildings is also crucial since many aren't megaquake-resilient. Tobin said there wasn't much money for this "piecemeal process."
"We have a really long way to go," he added.
Japan has known about its risk of giant earthquakes and tsunamis for centuries. It's one of the most prepared nations on Earth. And still, the 2011 subduction-zone rupture was devastating.
The Pacific Northwest, by contrast, only found out about the danger posed by the Cascadia subduction zone in the 1980s.
"Preparing for this is like trying to drain an Olympic-sized swimming pool with a teaspoon," Ezelle said.
Science could help better prepare for the Big One
Ezelle said that to be "the best prepared that we could possibly be," the Pacific Northwest's roadways, buildings, airports, and other infrastructure would have to be rebuilt.
A more immediate, affordable strategy to save lives is building out a system that sends early warnings to phones — which already happens for many earthquakes but isn't a guarantee.
The sooner the phone warning blares, the more time people have to duck and cover. The next frontier for that, Tobin said, is laying cables with seismic instruments on the seafloor along the fault line. That's what he's trying to do at the Pacific Northwest Seismic Network.
In the meantime, Tobin and other researchers are working to map the fault's structure. Their latest study may have uncovered some good news: The Cascadia subduction zone could rupture in segments or smaller earthquakes rather than all at once as one giant event.
But which scenario will actually happen — one Big One or multiple big-ish ones — remains unclear.
"I don't lose sleep over it," said Tobin, who lives in Seattle beneath the snowy peaks of the Cascades.
The Cascadia subduction zone pushed those mountains up about 10 million years ago, carving the mountain range that makes the Pacific Northwest so stunning.
"The same thing that makes the earthquakes, I should say, is part of what makes it a beautiful place to live," he said.