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Seismic waves vibrated off an island near Africa and hit Canada. Their cause is a mystery



If seismic waves emerge near a island off and hit Canada, does anyone feel them?

Apparently not – judging by a phenomenon that materialized earlier this month.

Coverage of earthquakes on Globalnews.ca:


The unusual seismological phenomenon originated near the island of Mayotte, off the coast of Madagascar on Nov. 11.

They were detected early on by Twitter user @matarikipax, who posted U.S. Geological Survey data showing they were detected at a monitoring station in Kilima Mbogo, Kenya.

The same user tweeted that waves were also detected in Zambia, Ethiopia, Spain and New Zealand.

John Cassidy, an earthquake seismologist with Natural Resources Canada (NRCan), later joined the fray, saying that the waves were detected right across Canada, in Victoria, Haida Gwaii, Toronto, Ottawa and Halifax.

Clearly, the waves were spotted all over the planet.

But no one seems to have felt them, even where they originated – and that has given them an aura of mystery, Cassidy told Global News.

No one can accurately explain why they happened.

READ MORE: Magnitude 6.8 Earthquake strikes Greek tourist island

Typically, a tectonic earthquake generates primary waves and secondary waves (s-waves), but this one did not produce either.

The ground moved up and down every 17 seconds as the waves flowed – "very slow shaking," Cassidy said.

It's possible that an earthquake happened, but if it did, the event was not a "typical" one, he added.

"Based on the seismic events and GPS formation data, there is likely a volcanic link – movement of magma chambers, etc.," Cassidy said.

The seismic waves originated in an area where an "earthquake swarm" occurred earlier this year.

Mayotte, which was formed by volcanic activity, saw "several hundred seismic events" recorded in the area starting in May, according to French geological surveyor BRGM.

The first happened on May 10. Then, five days later, the neighboring island of Comoros experienced a magnitude-5.8 earthquake, which was the largest it had ever recorded.

On Thursday, May 29, 2006, on Grand Comore, the largest of the three Comoros islands. Mount Karthala last erupted in April 2005.

AP Photo / Julie Morin

More seismic events have taken place in the area but they've tapered off since July.

"This indicates that the seismic energy released has been weakened since the start of the crisis, although some earthquakes are still being felt by the population," said BRGM.

The cause of the swarm is still being investigated, but researchers believe it could be a combination of tectonic and volcanic effects – although that has not been confirmed yet.

B.C.'s Interior area experienced an earthquake swarm in 2007, after it had never recorded quakes in past.

The swarm was attributed to the magma being injected into the lower crust under the Anahim volcanic belt, a phenomenon that produces "high-frequency, volcanic-tectonic earthquakes and spasmodic bursts."

READ MORE: 3 earthquakes measuring between 6.5- and 6.8-magnitude hit off Vancouver Island

Should volcanic activity be confirmed near Mayotte, then this would be the first to hit the area in over 4,000 years.

And these matters to Western Canada, Cassidy noted – there, too, there are a number of volcanoes that have been dormant for thousands of years and they could activate again in the future.

"Understanding these signals from Mayotte will help us better understand volcanic hazards here in Canada," he said.

© 2018 Global News, a division of Corus Entertainment Inc.


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