Scientists are losing explanation for the strange seismic incident that caused November 11 earthquakes and captured by earthquake sensors all over the world.
While the cause of this mysterious disorder remains unknown, it is somehow associated with an ongoing seismic swarm, which has plagued the Mayotte archipelago for several months in the Indian Ocean – but what these unusual tremors ultimately mean remains unclear.
"I do not think I have seen anything like that," said Göran Ekström, a seismologist at Columbia University national geography about the November 11 anomaly.
Almost half a year before this strange signal came, seismologists were surprised by another kind of abnormal seismic activity in the same neighborhood: a swarm of hundreds of small and frequent earthquakes coming about 50 kilometers from the east coast of Mayotte.
An island and isle network lying halfway between Africa and Madagascar is governed by France, but is also claimed by the island island of Comoros.
On the morning of May 10, this area was rocked by an earthquake that appeared without warning and which did not come alone – followed by hundreds of tremors that still do not have to disappear.
The most dramatic of these events, the May 5.8 magnitude event, was the largest earthquake ever recorded in the Comorian Basin. While the swarm generally moderated intensity, it has grown 5.1 times this magnitude since this week as a subtle reminder that this earth turbulence is not over.
Whilst the earthquake sounds alarming, they are not necessarily dangerous events.
In this case, a preliminary analysis of the seismic swarm by researchers at the École normale supérieure in Paris suggests that tremors can not be considered only as a tectonic movement, which means that volcanic activity in the region must also be involved.
Which brings us to November 11th.
– ******* Pax (@matarikipax) November 11, 2018
Less than three weeks ago – during the corner, but on a day when the shakes of the swarm were not actually detected – the scientists noted something else: strange, long and flat vibrations that suffered consistently, with no pointed fluctuations signing the usual earthquake activity.
Instead, this "very low-frequency atypical signal," quoted by the French Bureau de Recherches Géologiques (BRGM), repeats the wave every 17 seconds, lasting a total of 20 minutes.
"There are many things we do not know about," said research engineer Nicolas Taillefer, head of the BRGM Department for Seismic and Volcanic Risk. national geography.
"It's something completely new in the signals at our stations."
Which does not say the team has no hypothesis. With what we already suspect of a seismic swarm, it is the best estimate of scientists that anomalous vibrations have also been associated with volcanic activity, perhaps due to the huge movement of magma under the Indian Ocean.
If so, it could explain something else: Mayotte is not stationary.
GPS measurements show that since July – after the launch of the swarm – the island moved about 60 mm east and 30 mm south.
According to one analysis, this movement could be caused by the emptying of a magmatic reservoir nearby, although further research is needed to verify it.
SBV, like other stations, has a long monochromatic signal with ~ 17 s (Rayleigh's monofrequency wave). But filtered over 1Hz SBV (lower graph) also shows seismic (?) Signals from recurrent sources with about 50s apart. Maybe some big, shallow, oscillating volcanic source? pic.twitter.com/bPqdQFwAgm
– Anthony Lomax 🌍🇪🇺 (@ALomaxNet) November 11, 2018
If the hypothesis turns out to be correct, no one can say for sure what can happen, but modeling suggests that Mayotte can continue moving until the swarm persists.
Regarding whether we meet the mysterious signal again, nobody knows.
"These observations have therefore supported the hypothesis of a combination of tectonic and volcanic effects that represent a geological phenomenon involving seismic and volcanic phenomena," explains BRGM.
"This hypothesis will have to be confirmed by future scientific studies."