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A rare type of deep-earth tremor caused by a fierce storm dubbed a “weather bomb” has been detected – and it could shed new light on the Earth’s interior.
It’s the first time scientists have observed this particular type of tremor on the sea floor, known as an S wave microseism.
Tracking these elusive, faint tremors could help geoscientists map the different materials that make up the Earth’s interior because tremors change direction depending on the type of material they pass through.
Faint tremors called microseisms are phenomena caused by the sloshing of the ocean's waves on the solid Earth floor during storms.
Thanks to weather bombs - violent storms when atmospheric pressure drops rapidly - oceanic waves become so strong that a tiny portion of their energy reaches the sea floor and shakes it in the form of seismic waves, as if a very weak earthquake has occurred, New Scientist reported.
David Rothery, Professor of Planetary Geosciences at the Open University stressed though that the weather bomb that shook the Earth is not an earthquake per se.
To spot the tremor, researchers at Tohoku University used a network of seismic sensors in Japan to detect the rare S wave tremor, which originated from a cyclone over the North Atlantic Ocean off the coast of Greenland in December 2014.
Until now, experts had only detected P waves – the type of tremors that animals can feel before an earthquake – but could not detect more elusive S waves, which can be triggered by storms.
S waves cause material to ripple in a similar way to when a garden hose is jerked up and down, Science News explained.
By combining data collected by more than 200 sensitive seismometers operated by Japan’s National Research Institute for Earth Science and Disaster Prevention, the team was able to pick out S wave signals from the Earth’s seismic background noise.
In fact, the experts detected two types of S waves produced by the storm – SV waves that can turn into P waves and more mysterious SH waves that move material horizontally.
The observation, reported in the journal Science “gives seismologists a new tool with which to study Earth’s deeper structure,” the researchers wrote. They believe it will contribute to a clearer picture of Earth’s movements, even those originating from the atmosphere-ocean system.
“We’re potentially getting a suite of new seismic source locations that can be used to investigate the interior of the Earth,” said Peter Bromirski, a geophysical oceanographer at the Scripps Institution of Oceanography in California.
The scientists managed to determine both the direction and distance to these waves' origins, providing insight into their paths as well as the earthly structures through which they travelled.
In this way, the seismic energy travelling from this weather bomb storm through the Earth illuminated many dark patches of its interior.
Keith Koper, a seismologist at the University of Utah in Salt Lake City said combining the measurements of P, SV and SH waves will “ultimately provide better maps of Earth’s mantle and maybe even the core.”
The findings not only offer a new means by which to explore the Earth’s internal structure, but they may also contribute to more accurate detection of earthquakes and oceanic storms.
This article was originally published by WIRED UK
