Medium-sized earthquake off Vancouver Island lightly felt along West Coast

An earthquake measuring around magnitude 6.0 has shaken the seabed around 200 kilometres off Vancouver Island.

The U.S. National Tsunami Warning Center in Alaska says a dangerous wave is not expected from the quake.

The U.S. Geological Survey (USGS) website — which measured the quake at magnitude 6.0 — showed it was only lightly felt in areas ranging from Port Hardy, B.C., almost 250 kilometres from the epicentre, to Kitimat, B.C., more than 500 kilometres away.

It was felt down the West Coast as far south as Corona, Calif., almost 2,000 kilometres away, USGS said.

Earthquakes Canada estimated the quake, which happened at about 9 a.m. PT local time, at magnitude 4.2 but later changed to magnitude 5.7. 

The earthquake was centred along the eastern edge of the Juan de Fuca plate off Vancouver Island.

Quakes are common off British Columbia's coast — although not usually of this size — as movement from several different plates and subduction zones set off thousands of them every year.

Measuring quakes

Seismologist Brinley Smith, with Natural Resources Canada, says fluctuations in reported magnitude values are commonplace, especially as scientists gather more information on a specific quake. 

He says Earthquake Canada's initial numbers are based on automatic magnitude solutions after a significant event is detected and verified by a seismic analyst.

Updates will be made to the posted magnitude, says Smith, as more information comes in from other stations that can locate the event and if there are better types of magnitude. 

"That's what happened in this case. Our current solution has a magnitude of 5.7, and we're still looking into that now even to make sure we have that finalized," he said. 

"The magnitude changing is pretty much a routine occurrence ... with these larger events because we want the best possible analysis."