June 12, 2013 8:49 am
Updated: June 12, 2013 9:48 am

B.C. is ‘in the risk zone’ for mega-earthquake along the coast: study

Say goodbye to blue skies. Cloud has moved in to southern B.C. and there is a chance of rain and thunderstorms over the long weekend.

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VANCOUVER – A new study says the Pacific coast has experienced 22 major earthquakes over the last 11,000 years, and is due for another.

The study looked at sediment disturbance in Effingham Inlet, on the west coast of Vancouver Island.

Study author Audrey Dallimore, of Royal Roads University, says researchers using state-of-the-art radiocarbon dating determined the last so-called megathrust earthquake in the zone that stretches from northern Vancouver Island down to California happened more than 3,000 years ago.

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The world’s largest earthquakes are all megathrust earthquakes, which occur when there is a slip along the fault between a subducting and overriding tectonic plate.

There has never been a megathrust earthquake along the west coast in the written history of Canada, but the study found that megathrust earthquakes occur about every 500 years in the region, although they can stretch out for up to 1,000 years.

“The last megathrust earthquake originating from the Cascadia subduction zone occurred in 1700 AD. Therefore, we are now in the risk zone of another earthquake,” Dallimore said in a statement.

“Even though it could be tomorrow or perhaps even centuries before it occurs, paleoseismic studies such as this one can help us understand the nature and frequency of rupture along the (zone), and help Canadian coastal communities to improve their hazard assessments and emergency preparedness plans.”

B.C. forms part of the Northern American portion of what is called the Pacific “Ring of Fire,” a 40,000 km horseshoe of ocean trenches and volcanic arcs where 90 per cent of the world’s earthquakes take place.

According to Natural Resources Canada, the Geological Survey of Canada records more than 1,000 earthquakes in western Canada each year. More than 100 magnitude-5 or greater earthquakes have been recorded in the ocean west of Vancouver Island in the past 70 years.

The research by experts at Royal Roads, the Geological Survey of Canada, UBC and the University of California is published in the current issue of the Canadian Journal of Earth Sciences.

© 2013 The Canadian Press

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