Seismic noise is made up of all the vibrations that constantly pass through the ground. However, during confinement, the part of the phenomenon linked to human activity was reduced in proportions never observed. According to an international study, a decrease of 50 to 80% has been recorded across the world.
Published in the journal Science on July 23, this survey coordinated by the Royal Observatory of Belgium mobilized 76 seismologists from 27 different countries.
We found the seismic noise level globally dropped by ~50% in March-May 2020. The seismic data correlate with mobility data (e.g. Google/Apple) showing that real-time seismology can be used to assess broad changes in human behaviour & lockdown dynamics, & without privacy issues. pic.twitter.com/yoPI0HysJB
– Stephen Hicks (@seismo_steve) July 23, 2020
Interviewed by Sciences et Avenir, Corentin Caudron, volcano-seismologist at the Institute for Research for Development (IRD) explains that the researchers “analyzed 337 stations from around the world, including 268 for which the data could be used”.
Of these, 185 reported a significant reduction in human-induced seismic noise. This corresponds to the virtual disappearance, during this period, of travel by train or car, the slowdown of industrial machines, the cessation of tourism … etc.
In their study, the scientists indicate that “the period of seismic silence of 2020 is the longest and the most significant reduction of anthropogenic seismic noise in the world on record.”
The sound of silence: Human-made #seismic noise reduced by 50% during containment! This is what reveals an international study published in the journal @ScienceMagazine in which @CoCaudron volcano-seismologist at IRD #Isterre took part https://t.co/WqkrZkxOWo pic.twitter.com/ge8NEFyuIJ
— IRD.fr (@ird_fr) July 24, 2020
The major drops have been recorded by “surface seismometers” in large cities such as Beijing, Milan, New York, Montreal or Paris. Schools are particularly concerned, with a seismic noise level 20% lower than that observed during school holidays.
But this seismic silence has also extended beyond the urban poles, “over several kilometers radially”, towards less densely populated areas and “hundreds of meters deep”.
The data recorded by seismologists account for the succession of confinements, first in China, then in Europe and finally elsewhere in the world.
Thanks to this discovery, the researchers hope to be able to identify new warning signs of earthquakes or volcanic eruptions. So many sound clues so far drowned in the seismic noise of human activities, which the confinement silenced.
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