Earthquakes Canada charted earthquakes around Vancouver Island over the past 30 days. (Earthquakes Canada)

An unusually large swarm of tremors is rocking the ocean floor off the west coast of Vancouver Island.

Since Tuesday, 17 quakes in the four to five magnitude range centred about 200 kilometres west of Port Hardy have been detected.

Earthquake scientist Garry Rogers with the Geological Survey of Canada said quake swarms happen several times a year in that area, but this one is lasting longer, and the earthquakes are larger, than normal.

"It's just a reminder that we live in a very active area, and that immediately west of Vancouver Island is where new ocean crust is being born, and where we would call a very active geological environment."

The largest so far has been a magnitude 5.2 quake on Aug. 27 at 1:17 p.m. PT, but likely none were felt by anyone on shore, said Rogers.

"The earthquakes are too far off shore to be felt, and they are way too small to cause any tsunami or wave action," he said.

A magnitude 3.4 quake on July 30 west of Seattle in Puget Sound was felt by residents of Vancouver Island.