On November 1, scientists recorded unusual seismic waves that swept around the world from Chile to Canada and New Zealand. Scientists have put forward several versions from volcanic activity and the movement of magma, which caused the horizontal displacement of the lithospheric plates to the sea monster. What do Russian geophysicists think about this?
What happened?
The source of unusual seismic waves was located about 20 km from the island of Mayotte (Comoros), which lies between Africa and Madagascar. The seismic event lasted about 20 minutes, the waves spread over about 10 thousand kilometers, and the instruments recorded an unusual "pattern" of low-frequency vibrations: a clear zigzag with a predominance of waves of the same type, repeating every 17 seconds, National Geographic reported.
This region cannot be called seismically calm: since the first half of May, a series of earthquakes took place near the island of Mayotte, the strongest of which was recorded on May 15, its magnitude reached 5.8. But by now the tremors have become weaker.
Lake Dziani on Mayota Island, Comoros.
Atypical case
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Lev Vinniki, head of the Department of the Internal Structure of the Earth at the Institute of Physics of the Earth, Russian Academy of Sciences, explained why the seismic event on November 11 is not like most others.
“The recording looks very different. When there is an earthquake, waves of different types come one after another with different periods of oscillation, - says Vinnik. - Earthquakes have a very characteristic record: first, longitudinal waves come, then transverse, then surface. All of these waves are polarized in different ways. And this recording is different - it lasts 15-20 minutes and its individual waves do not differ. It is a continuous oscillation with a period of 17 seconds. The period is also very strange. In general, it doesn't look like a normal earthquake."
Scientists are also surprised by the distance over which the waves spread, but the main thing is that there were signals, but the earthquake did not.
“Indeed, the signals from this region were recorded rather strange. Long-period recurring surface-type waves that propagate over long distances of more than 10 thousand km, while no seismic event was recorded at that place. Actually, the oddities that many scientists pay attention to are precisely this: a low-frequency and long-term monotonic signal from a place where there was no earthquake in the usual sense,”explained Grigory Steblov, professor of the Russian Academy of Sciences, chief researcher at the Institute of Physics of the Earth.
And who is to blame?
Steblov calls the movement of magma in the layers underlying the lithosphere as one of the possible causes of seismic waves. It is also associated with the so-called "quiet earthquakes" - movements of the earth's crust, but they are usually not accompanied by shocks that are characteristic of "classical" earthquakes. In this case, low-frequency noise may occur, which was recorded in different parts of the world. But this version contradicts the "seismic portrait" of the November 11 event.
“There should be high-frequency primary body waves, secondary shear waves, then surface waves. All this has a typical picture with a larger oscillation amplitude, with a smaller one, with the time gap between the arrival of the wave also longer, depending on the distance from the source. All this did not correspond to what was here,”the scientist says.
“But in the case of Mayotte Island, it can be assumed that there was magmatic activity. A well-known phenomenon is the tremor of volcanoes that precedes the eruption of [volcano - approx. Attic] - this is a low-frequency tremor, which suggests that processes are being prepared in the magma chamber, which are accompanied by collapse, the ejection of magma from the chamber … Many well-known scientists, and we can agree with them, suggest that it was magmatic activity that played a role,”says Steblov.
In general, the island of Mayotte is of volcanic origin, but for the last 4 thousand years there has been no volcanic activity in the region, says Professor of the Russian Academy of Sciences, chief researcher at the Institute of Physics of the Earth RAS Grigory Steblov. Moreover, the island is located where the thick continental crust merges with the relatively thin oceanic crust. Volcanic phenomena usually occur in such zones, the scientist notes.
In addition, the volcanic tremor was recorded by geodetic observation satellites, the scientist stressed. Such devices note slow movements that are not recorded by the seismograph.
“They showed that this island has moved a few centimeters since May to the southeast. And this may confirm that there, below the lithosphere, where the movement of magma occurs, this is precisely what manifested itself. This is a perfectly logical explanation. Rarely enough, Steblov said.
However, instrumental seismology has existed for only about a hundred years, the interlocutor reminds, and if such a phenomenon occurs once every several centuries, scientists have not yet had the opportunity to fix it.
What's next?
If it really was a tremor, then a volcanic eruption may follow.
“For this to be a harbinger, there must be a magma chamber. There is no information about this … Whether the camera was formed there or not - we need to find out. There are different ways of researching this. But this requires study and instrumental observation."