Scientists can not explain a strange seismic event that shook the planet on Nov. 11 and was picked up by earthquake sensors around the world.
Although the cause of this mysterious disorder is unknown, it is somehow linked to a persistent seismic swarm that rattled the Mayotte archipelago in the Indian Ocean for several months – but what this unusual shock ultimately means remains unclear.
"I do not think I've seen anything like that," said seismologist Göran Ekström of Columbia University National Geographic about the November 11 anomaly.
Almost exactly half a year before this strange When the signal popped up, seismologists were surprised by another kind of abnormal seismic activity in the same environment: a swarm of hundreds of small and frequent earthquakes, some 50 kilometers off the east coast of Mayotte arise from.
The network of islands, located about halfway between Africa and Madagascar and islands is dominated by France, but is also dominated by France the island state of Comoros.
On the morning of May 10th, this region was shaken by an earthquake that appeared without warning and did not come alone – followed by a series of hundreds of tremors that were still unfinished.
Th The most dramatic of these events – an event with a magnitude of 5.8 on May 15 – was the largest quake ever recorded in the Comorian Basin, and while the swarm generally has decreased in intensity, one served Resurgence of 5.1 magnitude just this week as not so much. subtle reminder that these earthly turbulences are not over.
Although earthquake swarms sound alarming, they are not necessarily dangerous events.
In this case, a preliminary analysis of the seismic swarm of researchers from the École normal supérieure in Paris suggests that the vibrations can not be taken into account. Only the tectonic movement, ie volcanic activity in the region, must be included.
Here we are on the 11th of November.
– ******* Pax (@matarikipax) November 11, 2018
Less than three weeks ago – during the swarm, but on a day when no swarms of quakes were actually detected – the scientists registered something else: a strange, long one and flat vibration that hummed constantly, without the spiky swings that are a signature of the usual quake activity. Instead, this "atypical very low frequency" signal "- to quote the French Bureau of Recherches Géologiques (BRGM) – repeated itself in a wave about every 17 seconds, which lasted a total of about 20 minutes.
" It There are many things we do not know, "researcher Nicolas Taillefer, head of the BRGM unit for seismic and volcanic risks, said National Geographic .
" It's something completely new in the Signals on our stations. "
Which does not mean that the team has no hypotheses, with what we already suspect about the seismic swarm, the researchers believe that the anomalous vibration is also related to volcanic activity, perhaps because of a huge one Movement of magma under the Indian Ocean.
If so, this may explain something else: Mayotte is not stationary.
GPS measurements show that the island has been inactive since the Beg Since July, the swarm has shifted east by about 60 mm and south by 30 mm.
According to an analysis, this movement may be due to the emptying of a magma vessel nearby, although further investigation would be required.
SBV shows like the other stations a long monochromatic signal with ~ 17s (Rayleigh mono frequency) waves?). However, SBV filtered lower than 1 Hz (bottom curve) also shows seismic (?) Signals from repetitive sources at approximately 50s intervals. Maybe a big, flat, oscillating volcano source? pic.twitter.com/bPqdQFwAgm
– Anthony Lomax (@ALomaxNet) November 11, 2018
If the hypothesis turns out to be correct, no one can say with certainty what might happen, but the Modeling suggests that Mayotte can move as long as the swarm stops.
Nobody knows if we will hit the mysterious signal again.
"These observations therefore support the hypothesis of a combination of tectonic and volcanic effects responsible for a geological phenomenon involving a seismic sequence and a volcanic phenomenon," explains the BRGM.
"This hypothesis must be confirmed by future scientific studies."