A magnitude 9 earthquake and towering tsunami killed more than 15,000 people along Japan's northeastern coast and left more than 2,500 missing on March 11, 2011.

The subsequent disaster at the Fukushima nuclear plant left the nation's prime minister on the brink of evacuating Tokyo after the worst nuclear accident since Chernobyl.

Now scientists say it is only a matter of when a devastating earthquake and massive tsunami hits the U.S., specifically the Pacific Northwest, potentially killing thousands, CBS News reported.

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A magnitude 9 earthquake and towering tsunami killed more than 15,000 people along Japan's northeastern coast and left more than 2,500 missing on March 11, 2011. The devastation at the time pictured

The disaster at Tokyo Electric Power Co's Fukushima Daiichi nuclear plant washed away entire cities and left areas devastated after the worst nuclear accident in a quarter century. Above police search for survivors

Now scientists say it is only a matter of when a devastating earthquake and massive tsunami hits the U.S., specifically the Pacific Northwest, potentially leaving thousands dead. Seattle's Golden Gardens beach above

Experts also say the seismic event has the potential to be the greatest natural disaster ever experienced in the country, displacing one million people.

'This would be like five or six Katrinas all at once, up and down from California to Canada, would be the closest thing I can think of,' Chris Goldfinger, a paleo-seismologist at Oregon State University, told CBS.

Goldfinger, whose research indicates much of the region is overdue for a major quake, estimates there is a one-in-three chance it will strike in the next 50 years.

When asked how prepared the country would be for it, he replied, 'we're not completely unprepared, but we're pretty darn close,' adding on a scale of one to ten 'we're probably a little shy of one.'

The paleo-seismologist explained that Ground Zero is the 700-mile long area off the Pacific Coast called the Cascadia Subduction Zone.

There the North American tectonic plate is met with another plate, the Juan de Fuca.

One of the plates is sliding under the other plate, causing them to converge, but they are stuck.

'And so what happens is the weaker plate, which is North America, buckles,' Goldfinger said.

Experts say the seismic event has the potential to be the greatest natural disaster ever experienced in the country, displacing one million people from California to Canada

The Cascadia Subduction Zone is where the North American tectonic plate meets another plate, the Juan de Fuca. The two plates are converging but are stuck, which will cause the weaker North American plate to buckle

The downtown skyline in Portland, Oregon pictured. Chris Goldfinger, a paleo-seismologist at Oregon State University, estimates estimates there is a one-in-three chance a major quake will strike in the next 50 years

'And eventually something's going to give, and so the coastline that's been jacked up over 500-ish years or so is going to drop about a meter in about a minute or so.'

This would be the potentially devastating earthquake that would be followed by a colossal tsunami with waves reaching up to 50 feet on shore and stretching miles inland, CBS reported.

The devastation caused by the natural disaster could include large parts of Portland, Seattle and Vancouver left crumbling; communities stranded with impassable coastal towns, bridges and roads; and a collapsed economy in the region.

The threat of a megaquake is one the government is reportedly taking seriously.

The Federal Emergency Management Agency (FEMA) has spent years preparing the federal response to an earthquake and tsunami in the Pacific Northwest.

The agency estimates that in a best-case scenario there would only be 10,000 dead as a result of the natural disaster, assuming there are no beach tourists.

'Depending on when it happens, we're talking numbers that this nation I'm not sure is really prepared to deal with,' Ken Murphy, the Administrator for Region X of FEMA told CBS.

As the threat of a major quake is real, some communities are already preparing. In Westport, Washington, an elementary school is building the country's first vertical evacuation structure, featuring 44-ft-high walls and safe, high ground on its roof (pictured)

When asked if this could potentially be the greatest natural disaster the U.S. has experienced, Murphy replied: 'I would say it has the potential for that. This is an event you send everything to, and scale back down if you don't need it.'

Some of the locations at-risk if a major quake hits includes Seaside, Oregon's school complex holding 1,500 students.

Structural engineers say a large portion of the building would collapse in a seismic event, Superintendent Dough Dougherty told CBS.

Seaside's high school is only feet away from the Pacific Ocean and three out of four of its schools are in the tsunami danger zone.

If disaster hit and students and staff were able to evacuate, they would only have between 15 and 20 minutes to get to high ground, which is 1.3 miles away, Dougherty explained.

'That's one of those other pieces that keeps me awake at night,' he said.

The school district attempted three years ago to move the campus outside the tsunami zone, but voters rejected the measure after learning it would take an 18 per cent property tax increase.

With no money from the federal government or the state, Dougherty plans to retire and work towards another ballot campaign for a new campus.

A landscape view is pictured a week after a tsunami swept through Sumatra, Indonesia in 2005

Meanwhile in Westport, Washington, an elementary school is building the country's first vertical evacuation structure, featuring 44-ft-high walls and safe, high ground on its roof.

Ocosta Elementary's emergency structure was made possible after voters approved an additional $2million for it.

Superintendent Paula Akerland noted that while community is not affluent, 'so it was a huge commitment,' the community was looking at the safety of future generations.

And while the thought of natural disaster like the one that emptied much of Japan's northeastern coast five years ago might be terrifying, Goldfinger suggests that might not be a bad thing.

'If you're really well-prepared, and the infrastructure is hardened, that can be the end of it,' he said.