About four billion people — roughly half the world's population — have reportedly been told to isolate themselves in their homes to prevent the spread of the coronavirus. And the major decrease in the hum of normal human activity has led to a surprising shift in Earth's vibrations.

Researchers who study the Earth's movement said the mandatory shutdown of transportation systems, businesses and other human activities has correlated with the planet shaking noticeably less than usual. A drop in seismic noise — the vibrations in the planet's crust — is giving scientists the rare chance to monitor small earthquakes, volcanic activity and other subtle tremors that are usually drowned out by the everyday movement of humans.

The quieter vibrations were observed by Thomas Lecocq, a seismologist at the Royal Observatory of Belgium in Brussels, and published this week in an article in the journal Nature. According to Lecocq, such a dramatic decrease in noise can typically only be experienced briefly around Christmas.

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Lecocq observed that in Belgium, vibrations caused by human activity have decreased by approximately one-third since COVID-19 isolation measures were introduced by the government. The reduction in noise directly correlates with the closing of schools, restaurants and other public spaces in the country on March 14 and the ban of all non-essential travel on March 18.

While individual human activity such as vehicle traffic or construction sites only cause small movements in the Earth's crust, together they produce a sizable amount of "background noise" that hinder scientists' ability to detect natural events at the same frequency.

Since quarantine measures were introduced, the surface seismometer at the Royal Observatory of Belgium has become more sensitive to quieter seismic activity that it would have previously missed, which could lead to better measurements of small quakes, quarry blasts, storms and crashing ocean waves.

Update for Brussels (Station BE.UCCS): The background level remains low and stable (~-33%). We've added more time to the plot so last weeks are more in context. #StayHomeBelgium #StayAtHome #StayHome @CrisiscenterBE pic.twitter.com/bRSPeuxNcG — Seismologie.be (@Seismologie_be) March 27, 2020

"This is really getting quiet now in Belgium," Lecocq said.

After Lecocq shared his code online, his findings were echoed by seismologists around the world. Researchers in New Zealand, Scotland, New Jersey, England and France have all tweeted similar reports of decreased noise since their respective isolation periods began.

Celeste Labedz, a graduate student in geophysics at the California Institute of Technology in Pasadena, tweeted that even Los Angeles is experiencing a similar reduction in noise. "The drop is seriously wild," she said.

"How does @Princeton 'sound' different now that everyone must #stayathome? Here is the seismic "noise" we record in the basement of Guyot Hall," seismologist Jessica Irving tweeted. "Campus really is quieter now, especially after the tighter restrictions were put in place."

However, many stations are specifically located in remote areas or deep underground to avoid picking up on human activity. These stations are likely to see a smaller decrease or no change at all in noise, said Emily Wolin, a geologist at the US Geological Survey in Albuquerque, New Mexico.

The number of coronavirus cases worldwide continues to skyrocket, with over 1 million confirmed positive cases and over 56,000 deaths as of Friday. But seismologic data show one promising detail — people are listening to health officials and staying home.