Scientists are still scratching their heads over a mysterious seismic wave that rang earthquake sensors around the world last month, but nobody felt them.
The waves were first recorded offshore from the French island of Mayotte located off the tip of Madagascar. Sensors in Zambia, Kenya, Ethiopia, Chile, New Zealand, Canada, and Hawaii all recorded over 20 minutes of what some are calling a hum that circled the earth. 1
News Corp Australia explains the strangeness of the wave this way: 2 earthquakes, by their very nature, usually register as short-sharp ‘cracks’.
As tensions in the Earth’s crust suddenly release, pulses of clearly identifiable seismic waves radiate outwards from where the slippage occurs.
- The first signal is called a Primary wave: high-frequency compression waves that radiate in bunches.
- Then comes a Secondary wave: these high-frequency waves tends to ‘wiggle’ somewhat more.
- Only then comes the surface waves: these slow, deep rumbles tend to linger, and can circle the Earth several times.
This event is notable in that no Primary or Secondary waves were detected. All that registered was the deep, resonate surface wave.
And it didn’t ‘rumble’ as an earthquake’s surface wave tends to. Instead, it maintained a much cleaner — almost musical — frequency. Some have likened the wave to the entire earth ringing like a bell, “maintaining a low-frequency monotone as it spread.” 2
It was an amateur seismologist who first noticed the November 11 wave while reviewing real-time seismograph data from reporting stations around the world that are posted on the U.S. Geological Survey’s website.6 “An earthquake enthusiast who uses the handle @matarikipax saw the curious zigzags and posted images of them to Twitter. That small action kicked off another ripple of sorts, on Twitter as researchers around the world attempted to suss out the source of the waves.”1
Cause for Concern?
With so little understood about the unusual phenomena, residents of Mayotte and others around the world are expressing concern. BRGM has stated that “the appearance of this earthquake swarm in May 2018 took scientists by surprise.” 5
Speaking on the seismic wave, seismologist Göran Ekström from Columbia University told National Geographic, “I don’t think I’ve seen anything like it.” 1
The event released a storm of Twitter speculations ranging from aliens to off-shore drilling, island building off the coast of China, a meteor strike to a volcano eruption in the deep ocean or even an ancient sea monster rising from the deep:
This is the recording of the ~09:30 UTC Southern Indian Ocean event from Kilima Mbogo, Kenya. The signal has had a highpass filter applied to it at 0.01 Hz, 0.05 Hz, 0.1 Hz & 0.2 Hz respectively. As can be seen the signal is very low frequency @stevenjgibbons @ALomaxNet pic.twitter.com/UnAYW4mf1q
— Jamie Gurney (@UKEQ_Bulletin) November 11, 2018
BRGM, the French agency for geoscience research, had already been monitoring Mayotte as the site of an “earthquake swarm” in which several hundred seismic events have been recorded on the island since May 2018 when a magnitude of 5.8 earthquake and was felt across the entire island. The seismic activity has continued at lesser magnitudes and scientists are working to understand the swarm.
At this point, BRGM lacks enough data to advise whether Mayotte could experience an earthquake of greater magnitude or even a significant volcanic eruption, though they do provide reassurance that the configuration of the ocean floor around Mayotte is not conducive to the development of tsunami waves. 3
From earthquakes to super storms to mass strandings of whales, lately, there have been a number of strange geological and meteorological events going on around the world. Do you think they are connected? What do you think may have been the cause of this strange phenomenon?
References and Credits
Photo credit: An aerial view of Mayotte’s South Island. Photography by Hemis
1Wei-Hass M. Strange waves rippled around the world, and nobody knows why. 28 November 2018.
2News Corp Australia Network. Strange seismic waves were picked up circling the globe on November 11. Now seismologists are trying to figure out why. 29 November 2018.
3BRGM. Earthquake swarm in Mayotte: Scientific FAQ. 10 December 2018.
4Dockrill P. A Mysterious Seismic Wave Recently Shook Earth, And Scientists Can’t Explain It. 29 November 2018. Science Alert.
5BRGM. Earthquake swarm in Mayotte: a clearer understanding is emerging. 13 December 2018.
6USGS. Real-time seismogram displays.
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