The earthquake struck at 12:41 p.m. local time about 50 kilometres off the west coast of Vancouver Island, according to the United States Geological Survey. Smaller aftershocks followed.

The precise magnitude of the earthquake shifted throughout the day as seismologists in Canada and the United States revised their data. Initial reports put it at a magnitude-6.7 quake, but that was changed several times.

British Columbians living in parts of the Island and as far east as Kelowna and Kamloops reported feeling the tremor.

It also wobbled the upper floors of Vancouver's City Hall and even gave pause to people in Seattle, said Heather Lyle, who runs provincewide earthquake drills with Emergency Management BC.

"It has been widely felt — mild swaying — but there are no reports of damage or injuries anywhere," she said, noting she didn't experience any shaking in her office in suburban Surrey, southeast of Vancouver.

Susan Lambert, president of the B.C. Teachers' Federation, felt three successive waves on the third floor of the Vancouver office building where she works.

"At first, you're putting it down to a truck rolling by or hitting the building, but then we were pretty sure it was an earthquake," she said.

"We did start to wonder if we should duck and cover, but then it subsided."

The shaking was caused by what's known as a crustal earthquake, which means it was believed to have occurred in the top 15 kilometres of the earth's crust.

That sort of quake isn't unusual for the region, said Garry Rogers, an earthquake scientist with the Geological Survey of Canada.

Rogers, who is based in the Vancouver Island community of Sidney, said hundreds of much smaller quakes happen in the same region each year.

Those quakes are sparked by the sideways shifting of two tectonic plates, called the Juan de Fuca and Explorer plates, along a boundary called the Nootka Fault.

Tsunamis only occur when plates shift up and down, raising mass amounts of ocean water.

The last quake similar-sized quake in the region was recorded in November 2004, said Rogers. He said quakes of that size occur in the area about once a decade.

Rogers added people in the area shouldn't be surprised if they feel smaller trembles in the coming week.

"There's a certainty there will be aftershocks," he said. "Already, we've had half-a-dozen, with the largest being 4.9. But there's going to be hundreds of aftershocks ... potentially measured over the next week."

The seismic event was exponentially smaller than the massive megathrust earthquake and subsequent tsunami that ravaged Japan in early March.

Even though the quake caused more Twitter buzz than real damage, Prof. Brent Ward of Simon Fraser University said it should serve as a strong reminder that west coast residents live in earthquake country.

"It's kind of a cautionary wake up call that people need to be prepared for a larger quake," said Ward, who teaches in the university's earth sciences department. "Because we will get one eventually."

Many experts agree the next Big One is overdue.

Between federal, provincial and municipal governments, there are numerous quake emergency response plans in place, though they aren't consistent.

A provincial autodialer that makes 1,000 calls in 20 minutes to everyone from RCMP to the coast guard went into action on Friday, and hundreds of emails and faxes were also sent immediately as well.

The next B.C. earthquake drill happens on Oct. 20, and will occur in tandem with drills in California, Utah and Nevada.

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