Earlier this month, seismic stations in Madagascar, Canada, picked up mysterious waves that sounded for more than 20 minutes, unbeknownst to most people.
Researchers and earthquake enthusiasts who spotted the signals originally reduced to an area off the island of Mayotte in the Indian Ocean.
But no one really knows what caused this strange event.
The slow waves detected in Mayotte on November 11 are those generally observed after a major earthquake and are known to travel great distances, but no earthquake of this type has occurred.
Researchers and earthquake enthusiasts who spotted the signals have reduced the original to an area off the island of Mayotte (pictured) in the Indian Ocean. But no one really knows what caused this strange event
"I do not think I have seen anything like it," Göran Ekström, a seismologist at Columbia University specializing in unusual earthquakes, told National Geographic.
But, he adds, "that does not mean that their cause is ultimately exotic."
A Twitter feed that caught the attention of the seismology community revealed the strange phenomenon on the morning of November 11th.
A thread on Twitter that caught the attention of the seismological community revealed the strange phenomenon on November 11 in the morning. Scientists and earthquake enthusiasts have striven to reduce it.
"It's an extremely strange and unusual seismic signal," Twitter The user @matarikipax wrote next to a seismograph read at Kilima Mbogo, Kenya.
During the day, others may have pointed the conversation to indicate where low-frequency waves had been detected: Chile, New Zealand, Canada and Hawaii.
The signals created by waves from Mayotte appeared healthy, with a zigzag pattern consisting mainly of a type of wave, which took 17 seconds to repeat, according to National Geographic.
Waves like this are called monochrome.
The strange waves were attributed to an origin about 15 miles from the French island, Mayotte
Scientists are working to understand what caused the mysterious waves of that day. Until now, many suspect being linked to an ongoing seismic swarm in the region that began last May.
But even then, there was no corresponding earthquake on November 11th.
Researchers from the French Geological Survey (BRGM) believe that this could be a sign that the magma beneath the volcanic island is moving offshore.
Others say there could have been a "slow" earthquake that simply went unnoticed or an underwater eruption.
"The confirmation of the location is located near the Comoros," say the researchers who discovered the discovery.
Experts say the complex geology of the region is making the problem even worse, potentially filtering some of the waves to produce a clear signal, reports NatGeo.
Scientists plan to study the ocean to find any additional information that may explain the mysterious phenomenon.
But at this point, experts agree that we do not really know what to blame.
How are earthquakes measured?
The magnitude of an earthquake differs from its intensity.
The magnitude of an earthquake refers to the measure of energy released at the origin of the earthquake.
The magnitude is calculated on the basis of measurements made on seismographs.
The intensity of an earthquake refers to the force of the tremor produced by the sensation.
A magnitude 5.3 earthquake struck the Channel Islands off the south coast of California at 10:30 am Thursday.
According to the United States Geological Survey, "Intensity is determined from effects on people, human structures and the natural environment".
Earthquakes occur below the surface of the Earth in a region called the hypocenter.
During an earthquake, part of a seismograph remains motionless and a part moves with the surface of the Earth.
The earthquake is then measured by the difference in position of the fixed and moving parts of the seismograph.