A major earthquake that rumbled across Vancouver Island was felt as far away as B.C.'s Okanagan Valley to the east and Seattle to the south, but caused no injuries and apparently little damage when it hit midday Friday.

The estimated 6.4-magnitude tremor occurred at 12:41 p.m. PT, with an epicentre about 50 kilometres off the west coast of the island, about 300 kilometres west of Vancouver.

Initial reports estimated the quake was as large as magnitude 6.8, but those estimates were later downgraded

No tsunami warning was issued.

Honn Kao, a research scientist at the Pacific Geosciences Centre in Victoria, said the tremor was significant but not large enough to present a danger in the ocean..

"Usually if the earthquake is bigger than magnitude 7, then there will certainly be a possibility that a significant tsunami can be generated," said Kao. "For an earthquake with this kind of magnitude ... although the possibility is still there ... we don't think the threat can be as devastating as those big ones."

Perry Schmunk, who runs the Long Beach Lodge near popular tourist destination Tofino, was standing on the beach and said the sand shifting suddenly under his feet felt like standing on a waterbed.

"It shook — not violently, but it started rolling significantly for about half a minute. It went on for quite a while."

Tofino is the closest community to the epicentre.

Buildings swayed

Buildings in Vancouver rocked as the energy from the quake rolled through the Lower Mainland.

"I was sitting at my computer when I felt a light swaying motion," Wendy Hunter, of Vancouver, said in an email to CBC News. "I’m not prone to dizzy spells, but thought I might be experiencing that until I stood up and could definitely tell things were moving ever so gently …The building didn’t make any noise, but some of my window mobiles clinked gently against the glass."

A downtown office worker had a similar experience.

"I was on the 17th floor of our office building on Burrard at Pender streets when the ceiling tiles and windows started making a crackling noise. Then the blinds started swaying and I could feel the building swaying. A co-worker and I immediately went under my desk for about two to three minutes until the floor stopped moving," said Peter Bates.

TransLink spokesman Drew Snider felt it in his office on the 17th floor of a Metrotown building in Burnaby, east of Vancouver.

"The blinds were swaying back and forth in the windows and it was really a cause for concern because it got so much more magnified by being up in the air. It continued swaying for about three minutes which was enough to make a few people nervous here," he said.

David Dickinson was watching television at home in Courtenay on the east coast of central Vancouver Island when it struck.

"I was watching the U.S. Open Tennis downstairs and while sitting on my couch I felt it beginning to move back and forth.... It didn't frighten me ... but it took my attention off the tennis match for a few minutes."

Crustal earthquake

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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.

Aftershocks expected

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."

As a precaution, the Washington state transportation department sent inspectors to check for damage at the Alaskan Way Viaduct, an aging elevated highway on the Seattle waterfront, as well as two other bridges.

With files from the CBC's Mike Clarke and The Canadian Press