The series of earthquakes that have rattled parts of Vancouver Island recently are not a prelude to the long-expected “Big One” that seismologists have predicted for years.
Seismologist John Cassidy, who works in the Sidney office of Natural Resources Canada, said the entire west coast is an active region of plate tectonics.
He said the six earthquakes that have hit off the Island’s west coast in recent weeks did not originate in the major subduction zone where the Juan de Fuca tectonic plate meets the North American plate.
That’s where an expected major earthquake that could be 9.0 in magnitude on the richter scale or higher (a.k.a the Big One) is expected to originate.
“These earthquakes are not related to that, and they are not adding or lessening the stress that has built up in the subduction zone,” Cassidy said.
“The recent earthquakes were in fairly close proximity to each other and were located in areas where smaller tectonic plates are sliding past each other. Earthquakes from the subduction zone where the Juan de Fuca tectonic plate collides directly with the North American plate are the biggest earthquakes that hit this area, but they are also the rarest.”
The latest earthquake, which struck on Halloween night about 200 kilometres west of Port Hardy at a depth of 10 kilometres, measured 4.9 magnitude.
It came on the heels of three relatively strong earthquakes, followed by two smaller ones, last month that were recorded off Vancouver Island, about 260 kilometres west of Tofino.
Those earthquakes ranged from 6.8 to 4.0 on the richter scale, but did not cause damage or a tsunami.
Cassidy said the earthquake on Halloween night was an aftershock from the previous earthquakes. More are likely, but it’s expected they will become less frequent and intense over time.
“We’re not overly concerned about these series of earthquakes, but people should be aware that this is a seismically active region where earthquakes can be expected, including the Big One at some point,” he said.
British Columbia is located on the Pacific Ring of Fire, an active seismic zone where thousands of mostly small earthquakes are recorded annually by sensors in the province.
The last notable earthquake felt by Islanders was on Dec. 30, 2015, when a 4.3-magnitude earthquake, centred approximately eight kilometres east of Sidney, between Victoria and Vancouver, shook Vancouver Island. The last time there was a significant earthquake nearby was a 6.8 magnitude shaker in 2001, which was centred south of Seattle.
The last massive earthquake that was centred in the major subduction zone where the Big One is expected took place on Jan. 26, 1700 and it was estimated to be more than 9.0 magnitude.
It’s estimated that a major quake happens in that region on average every 300 years.