Seismic sensors first picked up the event originating near an island between Madagascar and Africa. Then, alarm bells began ringing as far away as Chile, New Zealand and Canada.
Hawaii, almost exactly on the other side of the planet, also picked up the event.
Nobody knows what it was.
Meteorite? Submarine volcano? Nuclear test?
"I do not think I've seen anything like it,"National Geographic Reports Columbia University Symologist Goran Extreme as saying. "It does not mean that, in the end, the cause of them is exotic."
In the center of the mystery is the provincial island of Mayotte, positioned on halfway between Africa and Madagascar. It is subject to a swarm of earthquake since May. Most have been minimal, but the biggest – on May 8 – was the largest in the island's recorded history, topping magnitude 5.8.
But the earthquake swarm was in decline before the mysterious ringing was detected earlier this month.
Extreme, which specializes in the unusual earthquake, shows much about the November 11 event is weird. It was as if the planet rang as a bell, calculating a low-frequency monotone as it spread.
Earthquakes, by their very nature, typically register as short-shot & cracks. As tensions in the earth's crust suddenly release, pulses of clearly identifiable seismic waves bounce outwards from where the slippage occurs.
The first signal is called a primary wave: high-frequency compression waves that relax in bunches.
Then there is a second wave: the high-frequency waves tend to winger & # 39; Something more.
Only then comes the surface waves: the slow, deep ribbons tend to linger, and cross the ground several times.
The November 11 event is notable in that no primary or secondary waves are detected.
All that was registered was the deep, reasonable surface wave. And it does not have a ribbon & # 39; As a surface wave surface tends to. Instead, it kept a lot cleaner – almost musical – frequency.
National Geographic Report The French geological surveys suspects a new volcano may be developing off the coast of Mayotte. While the island was created by volcanic activity, it was dormant for more than 4,000 years.
The French believe the bizarre ringing can be generated by a movement of magma some 50cm off the shore and under deep water. This is supported by GPS Sensors detecting Mayotte has moved some 5km to the southeast in less than five months.
But there is a poor moped area. Exactly below the ocean can only be guests at.
Extrem believes the unusually pure signal may have been caused by magma slipping about inside a cell, or being forced through a gap in the suburface rocks.
But he is not sure.