Seismometers measure the seismic waves of large events such as earthquakes, volcanoes, bombs, etc. At the same time, they capture what is called seismic noise (environmental vibrations) from things like wind, rivers, ocean waves, and human activities (especially travel and industry). According to a new study by an international team of researchers, the Earth's seismic noise level dropped by an average of 50% between March and May 2020, during the Covid-19 blockade.
In a July 23, 2020 statement from Imperial College London, which participated in the study, the researchers said this quiet period was likely caused by the full global effect of social distancing measures, the closure of services and industry, and declines in tourism and travel. .
They said it is the longest and most pronounced silent period of seismic noise in recorded history.
Before this study, scientists knew that human-generated noise tends to muffle during quiet periods, for example, during the Christmas and New Year holidays in the Western Hemisphere, during the Chinese New Year in Asia, and even during on weekends and at night. However, the researchers said the drop in vibrations caused by Covid-19's blocking measures outshines those seen during such periods.
View larger. The | This map shows 268 seismometers in 117 countries, 185 of which detected a drop in seismic noise between March and May 2020. Image via Imperial College London.
The new research showed that the largest drops in vibrations were seen in the most densely populated areas, for example Singapore and New York City. Vibration drops were also recorded in remote areas such as the Black Forest of Germany and Rundu in Namibia. The statement explained:
The strongest drops were found in urban areas, but the study also found signatures of the blockage on sensors buried hundreds of meters underground ...
Stephen Hicks of Imperial College London is co-author of the study, which was published in the peer-reviewed journal on July 23. Science. Hicks said in the scientists' statement:
Our study uniquely highlights how much human activities affect solid Earth.
He added that the study could also allow scientists to see more clearly than ever what differentiates human and natural noise.
Image via Imperial College London.
For this study, the researchers analyzed seismic data from a global network of 268 seismic stations in 117 countries. They found significant noise reductions compared to before any crashes at 185 of those stations.
Starting in China in late January 2020, and followed by Europe and the rest of the world in March through April 2020, researchers tracked the "wave" of calm between March and May as blockade measures were taken globally. .
Citizen-owned seismometers (like the one shown above), which tend to measure the most localized noise, noted large drops around universities and schools around Cornwall in the UK and Boston in the US, 20% greater noise drop than observed during school vacations. Image via Imperial College London.
Countries like Barbados, where the blockade coincided with the tourist season, saw a 50% decrease in noise. This coincided with flight data that suggested tourists returned home in the weeks leading up to the official closure.
The study reports that early evidence of previously hidden earthquake signals, especially during the day, seemed much clearer on seismometers in urban areas during closure. The study authors hope their work will generate more research on seismic blockage, as well as finding previously hidden signs of earthquakes and volcanoes. Hicks said:
The blockages caused by the coronavirus pandemic may have given us an idea of how human and natural noise interacts with Earth. We hope this information will generate new studies that will help us better listen to Earth and understand natural signals that we would otherwise have missed.
Bottom line: The Covid-19 crash caused a global 50% reduction in human-bound Earth vibrations between March and May 2020.
Source: Global silencing of high frequency seismic noise due to pandemic blocking measures COVID-19
Via Imperial College London
