Pacific Northwest at risk for a mega earthquake

Every seismic tremor in British Columbia brings a question: Is it the Big One?

A U.S. scientist now says there's a 10 to 15 per cent chance a mega-earthquake will strike in the next 50 years.

Prof. Chris Goldfinger, a marine geologist with the Oregon State University, studied the fault that runs from southern B.C. to northern California, and discovered it was more complex than previously thought.

Rather than one earthquake zone that was prone to major earthquakes every 10,000 years, Goldfinger found there were actually two zones. The one at the north end of the fault -- southern B.C. to Oregon -- is where a 9.0-magnitude earthquake would likely hit.

He also said the area is long overdue for a major quake, based on the historical frequency of past tremors. Quakes with a magnitude of at least 8.2 have occurred 41 times during the past 10,000 years.

"Perhaps more striking than the probability numbers is that we can now say that we have already gone longer without an earthquake than 75 per cent of the known times between earthquakes in the last 10,000 years," Goldfinger said.

"And 50 years from now, that number will rise to 85 percent."

There is an even greater risk of an earthquake hitting the southern end of the fault -- from the middle of Oregon to northern California. Goldfinger said there is a 37 per cent chance of a major earthquake striking in the next 50 years.

While that area is prone to slightly less severe earthquakes, it would still have a magnitude of at least 8.0, and could send a tsunami crashing into B.C.

"At the southern end of the fault, the earthquakes tend to be a bit smaller, but more frequent," he said. "These are still magnitude-8 or greater events, which is similar to what took place in Chile, so the potential for damage is quite real."

The February earthquake in Chile was measured at 8.8, and it destroyed hundreds of thousands of buildings.

The last major earthquake to hit British Columbia happened in June 1946. It had a magnitude of 7.3, making it the largest onshore earthquake in Canada's history. It knocked over buildings in several communities, but only two deaths were linked to the tremor -- one of them in Seattle, when a man suffered a heart attack.

By contrast, the Big One could have a magnitude greater than 9.0, so powerful enough to radically alter the region's landscape. The last mega-earthquake struck the North Pacific Ocean in 1700. It was so powerful it pushed a tsunami across the North Pacific Ocean to Japan, where it hit with a height of nine metres.

And while it was previously thought major earthquakes occur every 500 years, Goldfinger says new research into the Cascadia Subduction Zone shows that major quakes happen in clusters.

That means it could take 1,000 years before a mega-earthquake strikes, and then they would rock the area every 250 years.

"We're just starting to understand the whole idea of clusters and there isn't consensus on whether we are in one or not, but that possibility does exist, which further suggests that we may experience a major earthquake sooner than later," Goldfinger said.

He traced the history of earthquakes in the Pacific Northwest by carbon-dating the mud and sand displaced by offshore tremors. When a major quake hits, it sends mud into undersea canyons, where it can be differentiated from the usual build-up of sediment.

Goldfinger is now convinced that the next major earthquake is on the horizon.

"It is not a question of if a major earthquake will strike, it is a matter of when. And the ‘when' is looking like it may not be that far in the future," he said.

Doc examines quake impact on Vancouver

A new Discovery Channel documentary "Monster Quake" examines what would happen to Vancouver if it were hit by a mega-quake and suggests its effects could be devastating.

Filmmaker Mark Miller of the Discovery Channel discussed the documentary on CTV's Canada AM on Friday.

"The question we really looked at in the documentary is: are the building codes really addressing this kind of earthquake?"

Filmmakers travelled to Chile to survey the extent of the damage to buildings after February's massive earthquake, because building codes there are similar to those in Vancouver.

"There was an interesting anomaly, as many of the building that collapsed or were damaged were the nest buildings," he said. "Our building codes don't address mega earthquakes."

He said current building codes only address an earthquake shaking for only a minute, verses up to four minutes for mega earthquake.

"There needs to be the political will to upgrade our buildings, build better schools and hospitals," Miller added.