A trio of large earthquakes struck within an hour of each other late Sunday night, followed by three smaller quakes, off Vancouver Island, about 275 miles west of Bellingham.
No damage or injuries were reported from the largest quakes — all between magnitude 6.5 and 6.8, according to the U.S. Geological Survey —and there was no immediate tsunami threat , according to a post at the National Tsunami Warning Center website.
Sunday night’s swarm of quakes occurred less than a week after the Great ShakeOut, a worldwide series of earthquake drills.
USGS geophysicist Amy Vaughan told The Associated Press that the quakes were lightly felt onshore.
A quake of 6.1 to 6.9 can cause serious damage in populated areas.
British seismologist Stephen Hicks said on Twitter that the shaking occurred on the Sovanco transform fault, which is near the San Juan de Fuca plate and the Cascadia subduction zone.
Scientists think that region is overdue for a massive earthquake, on the scale of 9.0 or greater.
“Looks like we have an earthquake triplet, folks!” Hicks tweeted about midnight West Coast time. “A question that continues to puzzle earthquake scientists: Why did the 3 fault segments, which were all presumably close to failure anyway, rupture in three separate earthquakes over an hour period, versus a single M7.0 rupture???”
A total of six earthquakes have been recorded within miles of each other since the first one, a magnitude 6.6 temblor that struck at 10:40 p.m. PDT Sunday.
That was followed by a 6.8 quake at 11:16 p.m., a 6.5 magnitude quake at 11:23 p.m., a 4.9 at 11:36 p.m., a 4.3 at 12:13 a.m. Monday, and a 4.4 at 1:43 a.m. Monday.
All six quakes were between 6 miles and 11 miles deep, according the PNSN website.
Canadian Broadcasting Corp.’s seismologist and meteorologist Johanna Wagstaffe reported that the quakes were relatively shallow in depth and showed a horizontal “strike-slip” movement, which lessened the tsunami threat.
“If any one of these quakes had hit closer to land, there would have been devastating consequences,” Wagstaffe reported on CBC.
By 8 a.m. PDT Monday, a total of 163 responses were received at the USGS “Did you feel it” citizen science web portal.