Scientists are congested by a 20-minute forest of mysterious seismic waves discovered earlier this month.
Anxiety occurred in the morning of November 11 near the archipelago of Mayotte, a collection of French islands in the Indian Ocean between Madagascar and Mozambique.
It is not clear whether this is caused by volcanic activity or meteor strike, but it has been sensitized by seismometers all over the world, from New Zealand to Canada – and even in Hawaii.
Goran Ekstrom, a seismologist at Columbia University, told National Geography: "I do not think I saw anything like that."
"That does not mean that, in the end, the cause is exotic," admitted Mr. Ekstrom, acknowledging that the seismic waves were very unusual.
Geologists shared their surprisingly low-frequency discoveries on Twitter, and Jamie Gurney, founder of the British Quartet Newsletter, among the first to note the event.
This is an event recording ~ 09:30 AM UTC Southern Indian Ocean from Kilima Mbogo, Kenya. The signal had a high pass filter that was applied at 0.01 Hz, 0.05 Hz, 0.1 Hz and 0.2 Hz. As can be seen, the signal is very low frequency @stevenjgibbons @ALomaxNet pic.twitter.com/UnAYW4mf1q
– Jamie Gurney (@UKEQ_Bulletin) November 11, 2018
Mr. Gurney was soon joined by Anthony Lomax, who suggested that the epicenter for rumbles was east of the Mayotte Archipelago – but even with a fixed location, the cause remained a mystery.
Numerous possibilities have been proposed, inspired by the fact that – despite the observed stations that detect seismic waves – there was no such earthquake in the morning.
Low frequency waves were particularly interesting for seismologists.
Assuming that the epicenter east of Mayotte, high-frequency SBV arrivals correspond to P & S from at least three sources similar to tectonic earthquakes, and the long wave train (upper trace) corresponds to the set of Rayleigh surface waves from these sources. pic.twitter.com/zOvAPFxonW
– Anthony Lomax ??? (@ALomaxNet) November 11, 2018
Common earthquakes result in strong compressed waves known as Primary or P-Waves. Here are the secondary or S-waves that are not so compressed and moving from one side to the other.
Both of these types of waves have higher frequencies.
Low-frequency surface waves, similar to those discovered by Mayotte, follow the last. Because of their low frequency, they are able to travel across the planet several times, ring a bit like bells.
But the secretive low frequency noise on November 11th did not precede P-waves or S-waves, according to seizmologies.
The most prominent proposition in the seismological community refers to what they called "seismic horns" – in essence an event involving many earthquakes that roll together.
But the earthquakes that had shaken Mayotte over the past 18 months were very small, and they have been smaller in the last few months.
There was no earthquake discovered on November 11 when the mysterious sound rang.
Scientists are continuing the investigation.