Seismic sensors for the first time attacked the event that developed near an island between Madagascar and Africa. Then alarm bells rang to Chile, New Zealand and Canada.
Hawaii, almost exactly on the other side of the planet, also has the & # 39; event & # 39; addressed.
Nobody knows what it was. 19659004] Meteorite? Submarine volcano nuclear test?
"I do not think I saw anything like that," National Geographic reports to the seismologist at Colombian University Göran Ekström. "That does not mean the cause is ultimately so exotic for her."
At the center of the mystery is the small island of Mayotte, which lies about half way between Africa and Madigaskar. It has been exposed to an earthquake swarm since May. Most were minor, but the largest ̵
. But the earthquake swarm had declined before the mysterious ringing was discovered earlier this month.
Ekström, who specializes in unusual earthquakes, points out that the November 11 event was strange. It was as if the planet were ringing like a bell, sustaining a monotone low-frequency signal.
Earthquakes are by nature normally registered as short-sharp "cracks". As stresses in the earth's crust suddenly dissipate, pulses of uniquely identifiable seismic waves radiate from where the slip occurs.
The first signal is called the primary wave: high-frequency compression waves that radiate in bundles.
Then there is a secondary wave: These high-frequency waves tend to "wobble" a little more.
Only then come the surface waves: These slow, deep rumble tend to linger and can orbit the earth several times.
The 11th of November The event is remarkable in that no primary or secondary waves were detected.
All that was registered was the deep, resonating surface wave. And it has not "rumbled" as the surface wave of an earthquake tends to. Instead, a much cleaner – almost musical – frequency was retained.
National Geographic reports that the French Geological Survey suspects that a new volcano could develop off the coast of Mayotte. While the island was created by volcanic activity, it has been slumbering for more than 4,000 years.
The French believe that the strange ringing was caused by a movement of the magma about 50 km off the coast and under deep water. This is supported by GPS sensors, which find that Mayotte moved about 5 cm to the southeast in less than five months.
However, this is a poorly mapped region. What exactly is under the ocean can only be guessed.
Ekström believes the unusually pure signal could be due to magma floating around in a chamber or being pushed through a gap in the subterranean rocks.
But he is not sure