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Scientists are unable to explain a strange seismic event that shook the planet on November 11 and that was detected by seismic sensors installed around the world.
Although the cause of this mysterious disturbance remains unknown, it is in some way related to an ongoing seismic swarm that resonates on the Mayotte archipelago in the Indian Ocean for several months – but the significance these unusual tremors are finally obscure.
"I do not think I have seen anything like it," said Göran Ekström, seismologist at Columbia University, at National Geographic about the anomaly November 11th.
Almost six months before this strange event. Seismologists were surprised by another type of anomalous seismic activity in the same neighborhood: a swarm of hundreds of small and frequent earthquakes originating from about fifty kilometers off the east coast of Mayotte.
The earthquake swarm (BRGM)
The network of islands and d & # 39; Islets, located roughly halfway between Africa and Madagascar, is governed by France, but is also claimed by the island nation of Comoros.
On the morning of May 10, this area was shaken by an earthquake that occurred without warning and that did not occur alone, followed by a series of hundreds of tremors that have yet to disappear.
Th The most dramatic of them – an event of magnitude 5.8 on May 15 – was the largest earthquake ever recorded in the Comoros basin and, although the intensity of the Since the swarm has generally decreased since then, a resurgence of magnitude 5.1 this week did not seem so pleasant. Subtle reminder that this earth turbulence is not over.
Seismic swarms seem alarming, but they are not necessarily dangerous events.
In this case, a preliminary badysis of the seismic swarm carried out by researchers from the École normale supérieure in Paris suggests that the tremors can not be explained by
Which brings us to 11 November .
This is an extremely strange and unusual seismic signal.
Recorded at Kilima Mbogo, Kenya … #earthquake https://t.co/GIHQWSXShd pic.twitter.com/FTSpNVTJ9B– ****** * Pax (@matarikipax) November 11, 2018
Less than three weeks ago – during the swarm, but a day when no swarming tremor was detected – scientists have recorded something else: a strange vibration, long and flat that buzzed steadily, without the spiky fluctuations that are a signature usual activity of the earthquake.
Instead, this "very low frequency atypical signal" – to quote the Bureau of Geological Research of France (BRGM) – repeated in one wave every 17 seconds, for about 20 minutes in total.
"There are many things we do not know," said Nicolas, a research engineer. National Geographic said Taillefer, head of BRGM's seismic and volcanic hazard unit.
"It's something quite new in the signals of our stations."
Which does not mean that the team does not have a hypothesis. According to what we already suspected from the seismic swarm, the researchers believe that abnormal vibrations are also related to volcanic activity, perhaps due to a huge movement of magma under the Indian Ocean.
This could also explain something else: Mayotte is not at a standstill.
GPS readings indicate that since July, after the start of the swarm, the island has shifted about 60 mm (2.4 inches) in length. east and 30 mm (1.2 inches) to the south.
According to one badysis, this movement may be due to the emptying of a nearby magma reservoir, although further research is needed to verify it.
The SBV, like the other stations, displays a long monochromatic signal with a period of ~ 17 s (single-freq Rayleigh waves?). But filtered above 1Hz SBV (lower plot) also displays seismic signals (?) From repeated sources, about 50 seconds apart. Maybe a large, shallow, oscillating volcanic source? pic.twitter.com/bPqdQFwAgm
– Anthony Lomax (@ALomaxNet) 11 November 2018
If the badumption is correct, no one can say for sure what could happen. , but the modeling indicates that Mayotte can continue to move as long as the swarm persists.
As to whether we will find the mysterious signal, no one knows.
"These observations therefore support the hypothesis of a combination of tectonics and volcanic effects representing a geological phenomenon involving a seismic sequence and a volcanic phenomenon," explains the BRGM.
"This hypothesis will have to be confirmed by future scientific studies."
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