Seismic waves rippled around the globe a few weeks ago, setting off sensors in places as far away as Hawaii, Canada, Zambia, and Ethiopia. Scientists picked up the rumbling — even though it seems that no humans felt the movement — but they are stumped about what caused it, National Geographic reports.
“I don’t think I’ve seen anything like it,” said Göran Ekström, a seismologist at Columbia University.
On the morning of November 11, seismic waves began rolling through the planet, starting 15 miles off the shore of Mayotte, a French island situated near the northern tip of Madagascar. From there, the waves moved across Africa, Europe, North, and South America — and over to Hawaii, which is 11,000 miles away. The waves set off sensors in Zambia, Kenya, Ethiopia, Chile, New Zealand, Canada, Spain, and Hawaii, lasting for more than 20 minutes. Stranger still, the waves had a monotone, low-frequency to them as they spread across the globe.
If you didn’t notice the unusual occurrence, you aren’t alone. It seems that not a single person around the world felt the rumble, and only one person spotted the signal on the U.S. Geological Survey’s real-time seismograms.
Twitter user @matarikipax saw the “odd and unusual seismic signal” and posted images of the reports from sensors in Kenya, Zambia, Ethiopia, Spain, and New Zealand.
Other earthquake enthusiasts jumped on the data, pinpointing its origin and speculating about what caused the movements.
— ******* Pax (@matarikipax) November 11, 2018
Ekström cautions that just because the movements are unusual, that doesn’t mean that the cause is.
“It doesn’t mean that, in the end, the cause of them is that exotic,” he said.
Still, the low-frequency waves are unusual. A typical earthquake is the result of a built-up release of tension within the planet. When that tension is finally released, it sends out a wave that moves in groups, with a primary release followed by secondary waves that move more like snakes with a side-to-side ripple. After those waves pass, then you see the sort of low-frequency waves that this event produced.
Research is still ongoing, but it looks like the tiny island of Mayotte has been experiencing a cluster of seismic waves since last May. The nation has been hit with hundreds of earthquakes in that time, a majority of which have been minor. Some have been larger, however, like the 5.8 magnitude quake that smacked Mayotte on May 15.
Scientists know that the island is moving. In just a few months, it has moved several inches to the southeast. Magma is moving closer to the surface in the area. Right now, the best guess is that it has something to do with that molten body triggering some sort of shift within the earth.