'Slow' earthquakes are hitting B.C. every 14 months

Friday, June 20, 2014, 10:39 AM - 'Slow' earthquakes lasting up to two weeks at a time hit Victoria and Nanaimo, B.C. every fourteen months -- and scientists at the University of Ottawa and the University of Berkeley in California have pinpointed the cause.

The quakes, which can release energy equivalent to a magnitude-7 tremor, go unnoticed by the general public because they happen over an extended period of time.

Scientists say the phenomenon is the result of a silica-rich fluid found in deep sections of subduction zones.

As plates at the bottom of the ocean shift due to pressure and temperature fluctuations they release the fluid into rocks, allowing the plates to slip past one another in a process that can generate movement that typically lasts between ten and fourteen days.

When the shaking stops the fourteen month process then begins again, ending with another slow quake.

Co-author of the study Pascal Audet told the National Post that 'telltale' signs of the process can be found in silica-rich quartz in rocks above subduction zones.

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The first slow earthquake was recorded on Vancouver Island twelve years ago. While standard earthquakes seem to happen randomly, 'slow' earthquakes happen with almost clockwork precision, making them somewhat easier to study.

PREDICTING THE NEXT BIG QUAKE

Researchers say the findings could help scientists predict seemingly random, 'ordinary' earthquakes in the future.

"Every time there is a slow earthquake that happens, it also puts a little bit more pressure on the part of the fault that produces the regular earthquakes," Audet told the CBC. "It puts the fault closer towards the next big earthquake."

Still, the team isn't sure if slow earthquakes are linked to regular seismic activity, and they'll have to wait for the next big quake to test the theory.

The complete paper can be found in the journal Nature.