PEOPLE MAKE A lot of noise. Cars rumbling along streets, planes roaring overhead, feet slapping the sidewalk—these and other actions create countless tiny vibrations in the ground. A global network of seismometers registers those oscillations 24/7. But since world leaders have urged citizens to stay home and maintain social distancing to slow the coronavirus pandemic, the hum of daily life has quieted.
Lulls in seismic activity have occurred in the past, generally in short spurts. But COVID-19—the disease caused by the novel coronavirus—has imposed a lengthy hush in populated regions across the planet. And seismometers on multiple continents are recording the shift.
Though scientists have noted a definite drop in human activity, it’s tough to draw conclusions about how well social distancing is working from seismic data alone, Lecocq says. The magnitude of the change depends on many factors, including population density and nearby industrial activity. Even the position of a seismometer within a city can influence the size of the lull. In Brussels, seismic activity since the advent of COVID-19 is about 30 to 50 percent lower than average—similar to declines during the Christmas holidays. In Nepal, the seismic plots of some cities show a stunning 80 percent drop.
Observations that began out of curiosity might prove valuable to seismology research in other ways. “Having a lower level of background noise is just like being in a quieter room,” says environmental seismologist Celeste Labedz, a PhD student at the California Institute of Technology. “We can hear more sounds.”