Seismic sensors for the first time picked up an event near the island between Madagascar and Africa. Then alarm calls rang out, like in Chile, New Zealand and Canada.
Hawaii, almost exactly on the other side of the planet, also raised an “event”.
No one knows what it was.
Meteorite? An underwater volcano? Nuclear test?
“I don’t think I’ve seen anything like that,” says National Geographic from a seismologist at Columbia University Göran Extrem. "This does not mean that in the end, the reason is that it is exotic."
In the center of the mystery is the tiny island of Mayotte, located about halfway between Africa and Madigascar. Since May, he has undergone the charm of earthquakes. Most of them were insignificant, but the largest – May 8 – was the largest in the history of the island, exceeding 5.8 points.
But the earthquake swarm was in decline before the mysterious ringing was discovered earlier this month.
Ekström specializing in unusual earthquakes, many points to the event of November 11, it was strange. It was as if the planet was ringing like a bell, supporting a low-frequency monotone as it propagated.
Earthquakes, by their very nature, are usually recorded as short-sharp “cracks”. As stresses in the earth's crust suddenly release, pulses of clearly identifiable seismic waves radiate outward from the point of creep.
The first signal is called the primary wave: high-frequency compression waves that radiate in beams.
Then comes the secondary wave: these high-frequency waves tend to “wiggle” a bit more.
Only then do surface waves: these slow, deep thunders, as a rule, linger and can bypass the Earth several times.
The November 11th event is notable in that no primary or secondary waves were detected.
All that was recorded was a deep, resonating surface wave. And he didn’t “rumble”, as the surface wave of the earthquake takes place. Instead, he maintained a much cleaner, almost musical frequency.
National Geographic reports that the French Geological Survey suspects that a new volcano may be developing off the coast of Mayotte. Although the island was created by volcanic activity, it has been inactive for over 4000 years.
The French believe that the strange jingle may have been caused by a magma movement 50 km from the coast and under deep water. This is confirmed by GPS sensors that detect that Mayotte has moved 5 cm to the southeast in less than five months.
But this is a poorly displayed region. It is certain that under the ocean one can only guess.
Extrem believes that an unusually clean signal could be caused by magma breaking through inside the chamber or forced through a gap in subsurface rocks.
But he is not sure.