On the morning of November 11 low-frequency waves rumbled around the world for 20 minutes.
The mysterious seismic waves in the Indian Ocean were picked up by monitoring stations from Madagascar to Canada.
The discovery has baffled researchers, who said there were no reports of a large earthquake corresponding with the waves.
Activity like this is typically seen after large earthquakes but no such thing took place.
The waves buzzed across Africa, ringing sensors in Zambia, Kenya, and Ethiopia.
Sensors across Chile, New Zealand, Canada, and even Hawaii nearly 11,000 miles away also picked the signal up.
Theories as to what caused the Indian Ocean mystery include an undetected meteor strike, an underwater volcanic eruption and even an ancient sea monster.
The waves were picked up by seismographs almost 11,000 miles from Mayotte, an archipelago in the Indian Ocean between Madagascar and the coast of Mozambique, but were spotted by pure chance.
And only one person noticed the odd signal on the US Geological Survey’s real-time seismogram displays.
Göran Ekström, a seismologist who specialises in unusual earthquakes, told National Geographic: “I don’t think I’ve seen anything like it.
“It doesn’t mean that, in the end, the cause of them is that exotic.”
And researchers are still looking for an answer to the mysterious waves, however they are not without any leads.
According to Bureau de Recherches Géologiques (BRGM) GPS stations on Mayotte have tracked the island sliding more than 2.4 inches to the east and 1.2 inches to the south.
Nicolas Taillefer, head of the seismic and volcanic risk unit at BRGM told National Geographic: “The location of the swarm is on the edge of the [geological] maps we have.
“There are a lot things we don’t know, it’s something quite new in the signals on our stations.”
But Mr Taillefer notes the BRGM report from November 12 measured about a third of a cubic mile is squishing its way through the subsurface near Mayotte.
And Ekström thinks the mysteries rumble on the morning of November 11 actually did begin with an earthquake equivalent to a magnitude 5 temblor.
He said the reason it passed by largely unnoticed, was because it was what’s known as a slow earthquake.
He said: “The same deformation happens, but it doesn’t happen as a jolt.”