B.C. in 'window' of higher earthquake risk

Last Updated: Friday, February 2, 2007 | 9:05 AM PT

CBC News

Seismic scientists say there is a greater probability of a major earthquake on B.C.'s South Coast in the next week, following a series of minor quakes that have worked their way up from Washington.

But seismologist Garry Rogers of the Geological Survey of Canada added that despite the increased probability of a big quake, the chances are still very low.

He and other scientists at the Geological Survey were able to predict the series of tiny tremors which moved along the Cascadia fault line from Puget Sound to Vancouver Island in the past week, he said.

"It's the first time we've had an insight into a time behaviour, and in fact, quite a predictable time behaviour on a major fault, where we know major earthquakes occur. 

"What's going on right now is that the bottom portion of that fault is failing, and every time that happens, we're adding an increment of stress to the top portion that will eventually fail in a large earthquake. So when that is most likely to fail is when we are adding this increment of stress."

He and his colleagues are predicting a phenomenon called Episodic Tremor and Slip, or ETS, noting that ETS events occur in the area about every 14 months.

Each episode adds stress to the Cascadia fault line, and that makes it more likely that a major earthquake will occur, Rogers said.

"We are now in a higher window, or higher probability, if you like, for a big subduction earthquake, and we will be in a higher window for the next week or so as this event plays out."

Rogers also noted that scientists are still a long way from accurately forecasting major earthquakes. But if the big one doesn't hit B.C. this time, he said the next window of high earthquake risk will occur around April  2008.