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15 years of earthquakes in 45 seconds 0:47
(CNN) - During 2018, a multitude of seismic signals were detected by earthquake monitoring agencies around the world in May and June. A strange hum had been created and some of the signals detected in November of that year lasted up to 20 minutes.
The signals and the buzz aroused "the curiosity of the scientific community", according to a new study that explains what happened: the formation of a new underwater volcano.
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The unusual amount of earthquakes was traced to the island of Mayotte in the Indian Ocean, one of the many that make up the Comoros archipelago that lies between Africa and Madagascar.
The scientists detected 7,000 tectonic earthquakes within the scope of the study. These types of earthquakes occur when Earth's tectonic plates get stuck as they move side by side. The pressure that allows them to move causes earthquakes.
The most severe earthquakes reached a magnitude of 5.9 in May 2018.
Simone Cesca works on the modeling of the magma movement.
The researchers also found 407 long-term seismic signals. These signals, called VLP, are harmonic and low, resembling a double bass or a large bell. And its 20-30 minute signals could be detected hundreds of kilometers away.
Earthquakes and signals came from about 35 kilometers off the east coast of the island. The researchers could not observe any sign of volcanic activity in this area, but they suspected that the magmatic processes could be forming one.
Unfortunately, there was no seismic network in this part of the ocean floor, which means they could only get measurements from the island, Madagascar and Africa.
But they noticed a decrease in the surface of the island by 17 centimeters, indicating activity related to earthquakes.
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The new seismological methods developed by the researchers helped them create a year's chronology to reconstruct what happened. His study was published this week in the journal Nature Geoscience .
The first phase included the magma rising rapidly from a mantle deposit almost 29 kilometers below the Earth's surface. This opened a channel at the bottom of the ocean, allowing magma to flow and begin to form a new underwater volcano.
An oceanographic campaign in May 2019 showed that a volcano had formed in the same place.
During the formation of the underwater volcano, the seismic activity fell and the ground of Mayotte fell. Then, the VLP signals began.
"We interpret this as a sign of the collapse of the deep magma chamber off the coast of Mayotte," said Eleonora Rivalta, co-author of the GFZ German Research Center for Geosciences. "It is the deepest and largest magma deposit in the upper mantle to date, which is beginning to empty abruptly," he added.
Despite how dramatic this all seems, it barely showed on the island itself. Mayotte is one of the four volcanic islands in its archipelago and houses about 260,000 people, according to the study. It broke out for the last time about 4,000 years ago.
"Because the seabed is 3 kilometers below the surface of the water, almost no one noticed the huge eruption," said Torsten Dahm, co-author of the study and professor of geophysics and seismology at the University of Potsdam in Germany. "However, there are still possible dangers for the island of Mayotte today, as the earth's crust over the deep reservoir could continue to collapse, causing stronger earthquakes," he completed.
tectonic platesVolcanoesUnderwater Volcano