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On November 11, 2018, a Twitter user going by @matarikipax spotted a weird signal on the U.S. Geological Survey's live seismogram page. The signal had been captured by equipment in Kilimambogo, Kenya.
Matarikpax posted an image of it with the message,
Then he saw it in data from Zambia and Ethiopia before looking farther away and finding it in Spain, and then eventually in his own corner of the world, Wellington, New Zealand.
Other seismic-savvy people soon joined in as the mysterious low-frequency rumble circled the globe for about 20 minutes.
It was also detected in,
Eventually, its source
was determined to be about 15 miles off of French
archipelago Mayotte, located off
Africa between Mozambique and the northern end of Madagascar.
Even so, he cautions.
Even so, it's got seismologists baffled.
And there's been no
seismic activity that corresponds to the November wave. Still, the
seismology community suspects it's somehow related to the recent
activity off Mayotte.
Slow, low-frequency waves
such as the mystery rumble are generally produced at the tail end
of intense earthquakes, but again, there hasn't been one
anywhere in the right time frame that we know of.
Most waves contain a cluster of waves at different speeds, or frequencies, that make for a fuzzy, complicated burst of a waveshape on monitoring equipment. The November wave was comprised of just a single frequency, and appeared as an unusually simple, clean zig-zag of about 17 seconds in length.
Helen Robinson at the University of Glasgow, mischievously suggests to National Geographic,
It could be surrounding rock is filtering out other waves. Supporting this possibility is that, when the lowest frequencies are filtered out of the waveform, noise appears that could be faint P and S signals are seen.
Independent seismologist
Anthony Lomax
tweeted the following image:
The bottom shows possible P- and S-wave echoes
when
the wave was filtered.
Maybe it was...
Before lunchtime on the 11th, consensus was gathering around the theory that the global ringing was from a massive phreatic eruption very deep in the ocean.
A depth of around 3,000 meters was suggested, although no supporting evidence of such an eruption has yet surfaced.
Evidence of an event perhaps similar to this was spotted accidentally by an airplane passenger flying over the Pacific Ocean south of Raoul Island in 2012 - a floating raft of pumice gave it away.
While no satellite
imagery of the suspect Mayotte location has been examined yet, it's
worth noting that no such weird wave was reported during the Raoul
event.
The Mayotte archipelago is volcanic in origin, and the last eruptions are believed to have been 4,000 years ago.
Trouble is,
As for the Nov. 11 puzzler,
Another possibility, says Ekström, is that it was an unnoticed slow quake, possibly about a magnitude 5.
Instead of the characteristic and dramatic snap of a regular earthquake, slow quakes occur over the course of minutes, gradually releasing built-up stress.
Obviously, the mystery makes seismologist want to know much more about this area of the ocean floor and similarly uncharted undersea locations elsewhere.
For now, it's a very intriguing riddle.
"Depending on what field and what time in history, 99.9 percent of the time, it's ordinary, or noise, or a mistake, and 0.1 percent, it's something. But that's just the way it goes. That's the way it should go. That's scientific advance."
Anthony Lomax
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