They used data collected by 268 seismic stations all over the world, and they found that noise reduction was particularly dramatic on the university campuses equipped with these instruments, because here human activity had virtually ceased.
What Koelemeijer and her colleagues witnessed during lockdown was essentially the Great Cutting-Out of Anthropogenic Seismic Noise.
“Earthquakes are often really lower frequencies than the seismic signals from human activities,” says Koelemeijer.
This “anthropogenic seismic noise,” as seismologists call it, comes from all manner of human activities, whether that’s running factories, operating cars or trains, or even holding concerts.
“It is truly exciting to see seismologists from all over the world maximize this once-in-a-lifetime opportunity to quantify anthropogenic noise (and the background seismic signals it has been hiding) by sharing their seismic data from the Covid lockdown period,” Lindsay writes.