Seismographs around the world are recording a decrease in seismic activity as a result of people staying home amid orders of social distancing or quarantine for the coronavirus pandemic covid-19.
These detectors measure seismic waves through the Earth’s crust, but they also detect moving humans, industry, and traffic in the form of high-frequency noise patterns. During the period of mandatory social distancing, the Belgian Royal Observatory geologist and seismologist Thomas Lecocq decided to look at the observatory’s seismograph and realized that the noise levels in Brussels were more like what it looks like during the winter holidays than it was to a day of work. Other seismologists in different parts of the world have found similar noise reduction in their local seismographs.
The surface station at the Royal Observatory of Belgium was once in a suburb, Lecocq told Gizmodo. But the city has expanded, and seismograph readings today reflect the bustling human activity in the city. “When it snows it is calm, and when there is a marathon we can see people running,” he said.
Lecocq studies subtle changes in seismic noise. There aren’t many earthquakes in Belgium, but by characterizing noise, they can figure out how to remove it to see weaker or more distant events. Furthermore, humans are not the only ones that generate seismic noise; wind and ocean do, too, and seismologists can use this noise to monitor and create estimated images of the Earth’s crust. Therefore, it made sense for the scientist to observe the impact of the ongoing covid-19 pandemic. The Royal Observatory of Belgium published on social networks the graph that shows the decrease in seismic noise.
The readings made sense to Susan Hough, a seismologist with the United States Geological Survey. “If almost everyone stayed home and hardly moved, noise levels during the day would be close to the usual levels at night,” he told Gizmodo in an email.
Other seismologists elsewhere have conducted their own analyzes on seismographs. The United Kingdom recorded a decrease in noise of a station along a highway, while stations in France Y New Zealand They have also detected a calmer seismic environment as people stay home. Lecocq wrote a tutorial for those interested in looking at other seismic stations.
“These charts are not much more than a scientific curiosity, but the temporary decrease in noise could be useful for seismologists, since they can extract more information from their seismic data,” Lecocq told Gizmodo. These seismographs now have a better sensitivity to higher frequency events whose signatures are stained by human activity, as well as wind and water table behavior. Not only is there less seismic noise, but there is also less audible noise; Lecocq envisioned a study that correlated audible noise with seismic noise, and even studied how audible noise has increased in cities, with the help of seismological data.
These measurements serve as a reminder of the ongoing pandemic and of the many ways that human behavior impacts the planet.