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During lockdown we were light on the Earth

The lack of activity during the COVID-19 lockdown between March and May caused human-linked vibrations in the Earth to drop by up to 50%.

According to research led by the Royal Observatory of Belgium, the net effect of social distancing measures, closure of services and industry, and drops in tourism was the longest and most pronounced quiet period of seismic noise in recorded history.

As a result, scientists could listen in to previously concealed earthquake signals and differentiate between human and natural seismic noise more clearly than ever before.

The decrease in human noise was most obvious in densely populated urban areas, but the study also found signatures of the lockdown on sensors buried hundreds of metres underground and in more remote areas.

“This is the first global study of the impact of the coronavirus anthropause on the solid Earth beneath our feet,” says Stephen Hicks from Imperial College London, co-author of a paper in the journal Science.

The project brought together more than 70 researchers from 66 institutions around the world. They looked at seismic data from 268 seismic stations in 117 countries and found significant noise reductions at 185 of them.

https://cosmosmagazine.com/wp-content/uploads/2020/07/Video1-Worldwide-noise-after-lockdown.mp4

Beginning in China in late January 2020, they tracked a wave of quietening between March and May as worldwide lockdown measures took hold.

The largest changes in vibrations were seen in areas such as Singapore and New York City, but falls also were seen in remote areas like Germany’s Black Forest and Rundu in Namibia. Countries like Barbados, where lockdown coincided with the tourist season, saw a 50% decrease.

Citizen-owned seismometers, which measure more localised noise, noted drops around universities and schools in Cornwall, UK, and Boston, US, that were 20% greater than during school holidays.

The researchers say this unique period provided the opportunity to listen to the Earth’s natural vibrations without the distortions of human input.

Previously concealed earthquake signals were much clearer on seismometers in urban areas, particularly during the day, and scientists could differentiate between human-caused noise and natural signals that might warn of upcoming natural disasters.

And that’s important, says lead author Thomas Lecocq from the Royal Observatory of Belgium.

“With increasing urbanisation and growing global populations, more people will be living in geologically hazardous areas. It will therefore become more important than ever to differentiate between natural and human-caused noise so that we can listen in and better monitor the ground movements beneath our feet.

“This study could help to kick-start this new field of study.”

The 268 seismic stations with usable data. Lockdown effects are observed in red at 185. Symbol size is scaled by the inverse of population density to emphasise stations in remote areas. Credit: Lecocq et al.

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