Strange seismic waves that rippled around world baffle scientists


from ABC News:

A mysterious ripple of seismic waves has travelled thousands of kilometres across the globe, tripping sensors throughout Africa, Canada, New Zealand, and Hawaii, seemingly without being felt by a single person.

Key points:

  • Seismic waves beginning off the coast of Mozambique triggered sensors in Kenya, Chile, New Zealand and Canada
  • The tremors lasted more than 20 minutes
  • The earthquake went unnoticed until it was picked up by an earthquake enthusiast online

The tremors started just off the shores of Mayotte, a French archipelago in the Indian Ocean between Madagascar and Africa, and would have flown under the radar if not for an earthquake enthusiast in New Zealand who had been tuned in to the US Geological Survey’s real-time seismogram displays online.

They posted images of the readings to Twitter, prompting researchers around the world to try to deduce where these bizarre waves came from.

Unlike traditional earthquakes, which produce a jolt of various high frequency waves, the readings from the Mayotte tremor picked up consistent low frequency waves that lasted more than 20 minutes. It was as though the planet rang like a bell.

Online theorists suggest covert nuclear tests, sea monsters, or a meteorite as the cause of the tremor, but Goran Ekstrom, a seismologist at Columbia University, told National Geographic the explanation was likely straight-forward.

“I don’t think I’ve seen anything like it [but] it doesn’t mean that, in the end, the cause of them is that exotic,” he said.

Professor Ekstrom suggests that the seismic event actually did begin with an earthquake. He thinks it passed by surreptitiously because it was a slow earthquake.

Slow earthquakes are quieter than traditional quakes because they come from a gradual release of stress that can stretch over a significant period of time.

“The same deformation happens, but it doesn’t happen as a jolt,” Professor Ekstrom said.

Since May this year, Mayotte has been subjected to what is known as an ‘earthquake swarm’; a cluster of hundreds of seismic events over a period of days or weeks, but the activity has significantly lessened in recent months.

Analysis by the French Geological Survey suggests the strange waves may indicate a mass movement of magma beneath the earth’s crust, such as a chamber collapse.

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