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Recent B.C. earthquakes linked to fracking, 'slow' tremors


Cheryl Santa Maria
Digital Reporter

Monday, January 4, 2016, 3:29 PM - Though similar in magnitude, separate reports on a pair of recent earthquakes in B.C. -- one that occurred in August 2015 and one that occurred on December 29, 2015 -- are the result of two different phenomena.

The August quake has been linked to fracking -- i.e., the process of injecting a mix of water, chemicals and sand deep into the ground to extract natural gas from shale rock.

The December quake appears to be the result of a 'slow' slip, or tremors that occur over a period of several weeks.

FRACKING-TRIGGERED QUAKES HAVE HAPPENED IN B.C. BEFORE

In Mid-December, B.C.'s energy regulator confirmed that a 4.6-magnitude quake that occurred near Fort St. John in August was caused by operations at a gas fracking site operated by Progress Energy.

The epicentre of the quake was some 3 km from the fracking site. Nobody was injured during the incident and no damage was reported, but the quake could be felt for several kilometres, the CBC reports.

"This phenomenon is known as injection-induced seismicity, which has been documented for nearly half a century, with new cases identified recently in Arkansas, Ohio, Texas and Colorado," The USGS says on its website.

Fracking is said to be behind a recent spike in earthquakes in Oklahoma as well.

B.C. officials are looking into updating protocols to better protect the public from fracking-induced tremors.

'SLOW' EARTHQUAKES HITTING B.C. EVERY 14 MONTHS

On December 29, 2015 a 4.8-magnitude earthquake struck the Puget Sound region.

According to John Vidale of the Pacific Northwest Seismic Network, a 'slow slip' had been under Vancouver Island in the week leading up to the event, and may have played a role in the 4.8-quake, KUOW reports.

'Slow' earthquakes, which can release energy equivalent to a magnitude-7 tremor and last up to two weeks at a time, hit Victoria and Nanaimo, B.C. every 14 months, researchers say.

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 10 and 14 days.

When the shaking stops the 14 month process then begins again, ending with another slow quake.

The first slow earthquake was recorded on Vancouver Island 14 years ago. While standard earthquakes seem to happen randomly, 'slow' earthquakes happen with almost clockwork precision, making them somewhat easier to study.

Sources: CBC | KUOW

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