The reduction in atmospheric pollution following Covid-19 restrictions has been well publicised. The restrictions have also reduced noise—not only noise transmitted through the air, but seismic noise. Vibration from trains, aeroplanes, industry, and other sources is recorded on seismometers worldwide. Disentangling this noise is important to isolate natural signals of earthquakes, faults, volcanoes and so on. The human-made noise can also roughly track population movements. An article in the latest issue of Science describes recent world-wide work that found a substantial decrease in seismic noise corresponding closely with the timing of Covid-19 lockdown measures. Thus seismic noise offers a way to track and analyse aggregate human behaviour. — Thomas Lecocq and 75 others, “Global quieting of high-frequency seismic noise due to COVID-19 pandemic lockdown measures,” Science  369, no. 6509 (11 Sep 2020): 1338-43.

Fascinating, and yet another indication of the great impact that humanity has on the natural realm of which it is a part.