Canadian seismologists monitoring swarm of earthquakes off British Columbia coast


Robert Mittendorf
Mon, September 18, 2023 

Four moderate earthquakes shook the Pacific Ocean floor off Vancouver Island on Sunday, part of a “swarm” of nearly three dozen tremors over the past week that Canadian seismologists are watching.

No injuries were reported and no tsunami warning was issued for the four largest quakes, which ranged between magnitude 4.1 and 5.6 over a period of five hours early Sunday.

“We are currently monitoring a swarm of earthquakes far off the coast of northern Vancouver Island. There have been more than 30 events since (Thursday), though none have been felt and currently the largest reported magnitude is (5.6),” Earthquakes Canada said online.

Four of the largest quakes were centered about 350 miles northwest of Bellingham.

Seven people filed reports saying that they felt the 5.6 magnitude quake at the U.S. Geological Survey’s website.

A quake of magnitude 5.5 to 6.0 can cause slight damage to buildings, according to the Michigan Technological University Department of Geological and Mining Engineering and Sciences.

Only about 350 quakes of that magnitude are recorded worldwide every year, according to Michigan Tech.

Even though the tremors have caught the eye of Canadian seismologists, the head of the Pacific Northwest Seismic Network wasn’t too concerned.

A screenshot from the U.S. Geological Survey website show the location of a 5.6 magnitude earthquake with a yellow star, along with dozens of smaller quakes marked with white dots on Sunday, Sept. 17, 2023.

“There is no special reason to anticipate that the quakes offshore Vancouver Island are foreshocks to anything, any more than any earthquake has a small chance (about 1 in 20) of being a foreshock to a larger event,” seismologist Harold Tobin told The Bellingham Herald in an email.

“Even if that did transpire in this case, these earthquakes are too far from the Bellingham region to be relevant to (that) area specifically,” Tobin said.

Tobin, a University of Washington seismologist, told The Herald that he’s far more concerned about the chance for a devastating earthquake on the Cascadia subduction zone, an event that would be catastrophic for the Northwest,

“The potential for a giant Cascadia subduction earthquake remains unchanged, in my view — meaning that we always have a chance of one of those and should always be prepared for that possibility. But that’s no different today or in the near future than it was before the most recent moderate quakes,” he said.