Unusual Seismic Waves Shook the World on Nov. 11, and Scientists Aren’t Sure Why

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Unusual seismic waves rippled across the world earlier this month, triggering speculation about their cause.

The waves started Nov. 11 about 15 miles off the coast of Mayotte, a French island in the Indian Ocean near Madagascar and the African continent, before it went across Africa and pinged sensors in Ethiopia, Zambia, Kenya, and elsewhere. Then, it went across the Atlantic Ocean, hitting Chile, Canada, Hawaii, New Zealand, and other areas, according to National Geographic.

The waves started Nov. 11 about 15 miles off the coast of Mayotte, a French island in the Indian Ocean near Madagascar and the African continent. Google Maps

“I don’t think I’ve seen anything like it,” Goran Ekstrom, a seismologist at Columbia University, told National Geographic, which added that he specializes in unusual seismic activity.

Anthony Lomax, who works as an independent seismology consultant, said that the activity was “'almost certainly” caused by undersea volcanic activity northeast of Mayotte, the Daily Mail reported. “There has been ongoing low-level seismic activity there since May,” he added. “Inflation/deflation and collapse of volcano calderas, and movement of magma under a volcano can produce a wide variety of seismic signals, including long period and repetitive waves like those observed November 11.”

Geologists made the strange seismic activity on Twitter, and Jamie Gurney, the founder of the U.K. Earthquake Bulletin, was among those who saw it first.

“As can be seen the signal is very low frequency,” Gurney wrote about an event in Kenya on Nov. 11.

Twitter user Matarikipax posted a photo of waveforms obtained from the U.S. Geological Survey’s live stream of seismogram displays, saying it’s “a most odd and unusual seismic signal.”

The U.S. Geological Survey has yet to issue a statement on the matter.

In a typical earthquake, according to Michigan Technological University website, there are first “P waves,” or “primary waves,” which are “the fastest kind of seismic wave, and, consequently, the first to ‘arrive’ at a seismic station.”

“The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air,” the website says.

After that comes “S waves,” or “secondary waves,” and are slower than P waves. They “can only move through solid rock, not through any liquid medium. It is this property of S waves that led seismologists to conclude that the Earth’s outer core is a liquid,” according to the school.

After S and P waves are lower frequency surface waves, which are “almost entirely responsible for the damage and destruction associated with earthquakes. This damage and the strength of the surface waves are reduced in deeper earthquakes,” the university says.

The lower frequency waves were what was detected around the world on Nov. 11, but there was no perceptible earthquake, which is why many were baffled. According to Sky News, citing researchers, there were no observable P waves or S waves during the event.

“Ekstrom thinks that the events on the morning of November 11 actually did begin with an earthquake of sorts equivalent to a magnitude 5 temblor. It passed by largely unnoticed, he suggests, because it was what’s known as a slow earthquake. These quakes are quieter than their speedy cousins since they come from a gradual release of stress that can stretch over minutes, hours, or even days,” wrote National Geographic.

That type of activity is often associated with volcanic eruptions. For example, the Mount Nyiragongo volcano in the Democratic Republic of Congo produced a similar “slow earthquake” and low-frequency waves. The same type of waves were present during this year’s Kilauea eruptions that lasted for weeks in Hawaii.

Meanwhile, the wave pattern on Nov. 11 was made up of one type of wave, taking 17 seconds to repeat, according to the Daily Mail.

Gurney, a graduate of the University of Plymouth, told the paper he had “no idea if a similar global signal of this nature has ever been observed.”

Some scientists have speculated the waves are related to an ongoing earthquake swarm in the region that started in May 2017. The largest quake to hit the area was a 5.8 on the Richter scale.