Mysterious seismic waves that swept the world this month have prompted scientists to scratch their heads.
On the morning of November 11, particular seismic ripples were detected 15 miles off the coast of Mayotte, a French island located between the Indian Ocean and Mozambique.
The strange waves pulsed for a total of 20 minutes, not felt by humans, according to National Geographic Thursday. They have apparently not caused any damage.
It seems that the event was noticed for the first time by a Twitter user @matarikipax who shared a seismogram display from the US Geological Survey of Kilima Mbogo, Kenya, noting, "This is a very strange and unusual seismic signal."
Just like the airwaves themselves, news of them have been relayed on Twitter by researchers speculating on their source. Theories and observations ranged from underwater volcanic eruptions and tectonic earthquakes at meteors and space weather.
"The event is almost certainly linked to a volcano, since Mayotte and the surrounding region are volcanic," theorized Anthony Lomax, an independent seismologist.
"The seismic waves may come from a rock-like earthquake reacting to inflation / deflation or the collapse of a volcanic edifice, or directly related to the movement or to the the vibration of the magma, "added Lomax.
Typical earthquakes trigger two types of body waves moving rapidly at high frequencies. The former are primary waves or P waves, which can move longitudinally through rock and liquids, and are sometimes felt by humans. Secondary waves or S waves can also be felt, but can not pass through a liquid and tend to shake the ground from one side to the other along its course.
These waves are supplemented by lower frequency surface waves, which may be responsible for the worst surface destruction following an earthquake.
What makes the November recordings strange is their long monochromatic signal. "On most seismometers in the world, the signal is long and almost entirely in a period – 17 seconds – without the higher frequency and typical P and S waves emitted by most earthquakes," Lomax said.
Until now, nothing has been permanently connected to the event.
Mayotte is part of an archipelago of volcanic islands called Comoro. The island itself has two volcanoes dormant for more than 4,000 years. however, National Geographic noted that hundreds of earthquakes had submerged Mayotte since May 2017 and that the French Geological Survey was currently monitoring the region to detect any new volcanic activity.