The lack of human activity during the blockage resulted in human-related vibrations on Earth declining by an average of 50% between March and May 2020. This “quiet period”, probably caused by the general global effect of social distancing measures, the closure of services and industries, and the decline of tourism and travel is the longest and most pronounced quiet period of seismic noise in human history. A new study by an international team of scientists showed that the attenuation of “seismic noise” caused by people was more pronounced in more densely populated areas. Research published by Science.
The relative silence allowed researchers to listen to previously hidden earthquake signals and could help us distinguish between human and natural seismic noise more clearly than ever before.
The Quiet Period is probably the longest and most significant attenuation of anthropogenic seismic noise since scientists began detailed monitoring of the Earth using extensive seismometer monitoring networks.
The study makes it clear how much human activity affects the solid Earth.
The measured seismic noise is caused by vibrations within the Earth that propagate like waves. Waves can be caused by earthquakes, volcanoes, and bombs, as well as daily human activities such as travel and industry.
In 2020, no earthquakes were observed, and the fall in anthropogenic seismic noise is unprecedented. The most severe falls were found in urban areas, but the study also found blocking signatures from sensors buried hundreds of meters underground and in more remote areas.
Human-generated noise is usually attenuated during quiet periods such as Christmas, New Year, and Chinese New Year, as well as during weekends and at night. However, the drop in vibrations caused by the COVID-19 lockout dwarfs even those seen during these periods.
Some researchers call this reduction in anthropogenic noise and pollution anthropause. This is the first global study of the impact of coronavirus anthropause on the solid Earth beneath our feet.
To collect the data, the researchers examined seismic data from a global network of 268 stations in 117 countries and found significant reductions in noise levels compared to any blockage at 185 of those stations. Starting with China in late January 2020, followed by Europe and the rest of the world from March to April 2020, researchers tracked a “wave” of calm between March and May, when restrictive measures were taken around the world.
Citizen-owned seismometers, which tend to measure more localized noise, have seen large drops at universities and schools in Cornwall, UK, and Boston, USA – 20% more noise reduction than during school holidays.
Countries such as Barbados, where localization coincided with the tourist season, saw noise levels drop by 50%. This coincided with flight data, according to which tourists were returning home several weeks before the official closure.
Over the past several decades, seismic noise has gradually increased as the economy and population grew.
The study reports the first evidence that previously hidden earthquake signals, especially during the daytime, on seismometers in urban areas seemed much clearer during the COVID-19 lockdown.
Loosening the blockage could also help them distinguish between man-made noise and natural signals, which could warn of impending natural disasters, the researchers say.
As urbanization increases and the world’s population grows, more and more people will live in geologically hazardous areas. Therefore, it is becoming more important than ever to distinguish between natural and man-made noise so that we can “listen” and better track the movement of the ground under our feet. This research can help start a new area of study.
Dr. Thomas Lecock, lead study author at the Royal Observatory of Belgium
The authors of the work hope that their work will lead to further studies of seismic localization, as well as the discovery of previously hidden signals from earthquakes and volcanoes.