VANCOUVER — Three relatively strong earthquakes that began Sunday night in the Pacific Ocean off Vancouver Island didn’t trigger a tsunami because they happened along a fault line where sections of the Earth’s crust are moving sideways, says an earthquake seismologist with Natural Resources Canada.
“That horizontal type of movement is the least likely to generate a tsunami, because there is no vertical movement of the sea floor. It’s a horizontal slipping,” John Cassidy said in an interview Monday from Victoria.
The U.S. Geological Survey reported a 6.6 magnitude quake about 260 kilometres west of Tofino, followed by a 6.8 tremor and then a third measuring 6.5.
Survey geophysicist Zachary Reeves in Golden, Colo., said all three quakes occurred in the same general area over about an hour and at a shallow depth of about 10 kilometres. He described the quakes as “pretty big.”
Emergency Info BC tweeted that the quakes were felt in parts of the province, but there were no reports of damage or injury.
At least four aftershocks were reported late Sunday or early Monday ranging in intensity from 5.2 to 4.3. Cassidy said more were expected.
“The most likely scenario now is that the aftershocks will continue for days or weeks, but they will become smaller as time goes on, and they will become less frequent,” he added.
About 200 people reported feeling the quakes to the U.S. Geological Survey website, most of them on the east coast of Vancouver Island.
Three earthquakes of the magnitude recorded within a 45-minute window are unusual, Cassidy said, but he added they don’t necessarily mean a damaging shaker is imminent.
“These are a very good reminder of plate motions and earthquakes that occur here in this region. We have seen much larger in the past and we will see larger again in the future.”
He said it is important to be aware of earthquakes so people “know what to expect and be prepared.”
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.
Most of the quakes happen near the Cascadia subduction zone, an area where the Juan de Fuca and North American tectonic plates converge, stretching from Vancouver Island to northern California.
An earthquake early-warning system recently tested off the B.C. coast could give residents anywhere from 20 seconds to two minutes to prepare before a quake.
The first-of-their-kind warning sensors developed by Ocean Networks Canada are installed along the Cascadia subduction zone and when fully operating next March will be able to estimate location and magnitude of a megathrust earthquake.