Mystery of the strange seismic waves that shook the world on Nov 11th SOLVED as expert claims they were caused by huge underwater volcano
Sensors first picked up the shockwaves near an island between Madagascar and Africa
SCIENTISTS have solved the mystery of unusual seismic waves that travelled around the world on November 11.
The waves were picked up by monitoring stations between Madagascar and Canada but could not be felt above ground.
The origin of the seismic waves has now been narrowed down to a region just off the coast of Mayotte, a French island between Africa and north Madagascar.
Although no earthquake took place, the shocks were similar to those typically seen after large earthquakes, which baffled scientists.
But one scientist studied the charts and has now confirmed the trembling was "almost certainly" caused by a low-level underwater volcanic eruption northeast of Myotte, reports the .
The tiny island of Mayotte, with a population of 250,000 people, has been subjected to a swarm of earthquakes since May.
Most have been minor, but the biggest — on May 8 — was the largest in the island's recorded history, with a magnitude of 5.8.
But the earthquake swarm had been in decline before the mysterious ringing was detected earlier this month.
The waves ricocheted and set off sensors in Zambia, Kenya and Ethiopia, before being picked up across Chile, New Zealand, Canada and even Hawaii, nearly 11,000 miles away, reports .
Earthquakes produce seismic waves which travel either on the surface of the Earth or through it.
Experts had been deliberating the cause of the event since November 11 and initially thought it could have been a nuclear test, submarine or volcano.
Robin Lacassin, of the Institut de Physique du Globe de Paris, alluded to the November 11 event as "an odd seismic signal linked to the Mayotte island earthquake swarm, that started in May".
On Twitter there was intense speculation as to its cause with independent seismology consultant Anthony Lomax suggesting it might have a "large, shallow, oscillating volcanic source";.
Colombia University seismologist Göran Ekström said: "I don’t think I’ve seen anything like it."
Ekström, who specialises in unusual earthquakes, points out much about the November 11 event was weird.
It was as though the planet rang like a bell, maintaining a low-frequency monotone as it spread.
National Geographic reports the French Geological Survey suspects a new volcano may be developing off the coast of Mayotte.
While the island was created by volcanic activity, it’s been dormant for more than 4,000 years.
What were the strange seismic waves that rippled around the world on November 11?
Many aspects of the waves were “weird, from their surprisingly monotone, low-frequency ‘ring’ to their global spread,” explains National Geographic.
It says that “in a normal earthquake the built-up tensions in Earth’s crust release with a jolt in mere seconds.
“This sends out a series of waves known as a ‘wave train’ that radiates from the point of rupture.”
The fastest of these are Primary waves, that move in bunches – similar to an extended slinky.
Next are the secondary waves, which have more of a side-to-side motion.
Both have relatively high frequencies – a “sort of ping rather than a rumbling,” explains Stephen Hicks, a seismologist at the University of Southampton.
However, the “strange signals” that emerged from Mayotte were slow, long-period surface waves.
If there was an intense earthquake, these can zip around the planet multiple times, ringing Earth like a bell, Hicks said.
But, on November 11 there was no big earthquake to kick off the slow waves.
Plus, Mayotte’s mystery waves are what scientist call monochromatic, adds National Geographic.
Most earthquakes send out waves containing different frequencies, but Mayotte’s signal was a “clean zigzag dominated by one type of wave that took a steady 17 seconds to repeat”, it explained.
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But it’s a poorly mapped region, and precisely what’s beneath the ocean can only be guessed at.
Ekström believed the unusually pure signal could have been caused by magma sloshing about inside a chamber, or being forced through a gap in the subsurface rocks, reports .
Jean-Paul Ampuero, a seismologist at the Université Côte d'Azur in France, told National Geographic that the seismic waves were like a “musical instrument. The notes of a music instrument – whether it’s grave or very pitchy – depends on the size of the instrument.”
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