​Anticipating the next mega-quake

Could a tsunami similar to the one that devastated Japan five years ago this week wreak the same kind of havoc along our northern Pacific Coast? Unfortunately, the experts say it's just a matter of time. Our Cover Story is reported by Don Dahler:

In March 2011 the world watched in awe and horror as a colossal tsunami ravaged eastern Japan -- the result of a 9.0 magnitude earthquake.

Entire cities were washed away; millions were stranded without power or water. 15,000 died.

It was an otherworldy event that happened thousands of miles away. Thank goodness, many Americans thought, it couldn't happen here.

But it could happen here.

In fact, scientists say it's a question of when -- not IF -- a devastating earthquake, followed by a huge tsunami, strikes the continental United States, right in the Pacific Northwest.

"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," said Chris Goldfinger, a paleo-seismologist at Oregon State University.

It may sound like a Hollywood disaster movie, but it's not; this is the future for the region's seven million people, says Goldfinger. His research shows much of the region is overdue for a major quake.

The last one was back in 1700 ... long before there were large cities right in harm's way. "If it happens anytime soon it woudl just devastate the area," he said.

Goldfinger estimates there's a one-in-three chance this quake will strike sometime in the next 50 years.

"We're not completely unprepared, but we're pretty darn close," he said. "On a scale of one to ten, we're probably a little shy of one at this point."

Ground Zero is the 700-mile-long area off the Pacific Coast called the Cascadia Subduction Zone, where the North American tectonic plate meets another plate known as the Juan de Fuca.

CBS News

The two plates are converging -- one sliding under the other -- but are stuck. "And so what happens is the weaker plate, which is North America, buckles," said Goldfinger. "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."

And that's just the earthquake. Next comes a tsunami, with waves as high as 50 feet roaring on shore, reaching miles inland.

It's a threat the government says it's taking seriously. Dahler asked Ken Murphy, the Administrator for Region X of the Federal Emergency Management Agency, "Is FEMA ready for the Big One?"

"I would never say we are ready," he replied.

The agency has spent years preparing the federal response to an earthquake and tsunami in the Pacific Northwest. FEMA's best-case scenario: 10,000 dead. And that's assuming no beach tourists, which would lead to their worst-case scenario -- simply too terrifying to contemplate.

Experts say the Pacific Northwest is overdue for a devastating earthquake and tsunami that could kill thousands (under the best-case scenario), but only some communities are preparing. CBS News

"Depending on when it happens, we're talking numbers that this nation I'm not sure is really prepared to deal with," said Murphy.

"Potentially the greatest natural disaster this country has ever experienced?" asked Dahler.

"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."

The quake could displace a million people from northern California to southern Canada. Large parts of Seattle, Portland and Vancouver will crumble. In coastal towns, roads and bridges will likely be impassable, stranding whole communities. The region's economy could collapse. Rebuilding might take years, even decades.

And few places are more at risk than Seaside, Oregon's school complex -- 1,500 students in four aging buildings.

"The structural engineers tell us that a vast majority of the building will collapse in a seismic event," said Superintendent Doug Dougherty.

Three of Seaside's four schools are also in the tsunami danger zone. Its high school is just feet away from the Pacific Ocean.