Global quieting of high-frequency seismic noise due to Covid-19 pandemic lockdown measures

Human activity causes vibrations that propagate into the ground as high-frequency seismic waves. Measures to mitigate the Covid-19 pandemic caused widespread changes in human activity, leading to a months-long reduction in seismic noise of up to 50%. The 2020 seismic noise quiet period is the longest and most prominent global anthropogenic seismic noise reduction on record. While the reduction is strongest at surface seismometers in populated areas, this seismic quiescence extends for many kilometers radially and hundreds of meters in depth.

This provides an opportunity to detect subtle signals from subsurface seismic sources that would have been concealed in noisier times and to benchmark sources of anthropogenic noise.

Thomas Lecocq and colleagues assessed the effects of Covid-19 lockdowns on high-Frequency (4–14 Hz) Seismic Ambient Noise (hiFSAN). They compiled a global seismic noise dataset using vertical-component seismic waveform data from 337 broadband and individually operated citizen seismometer stations, such as Raspberry Shakes (RS), with a self-noise well below the ground motion generated by anthropogenic noise, and flat responses in the target frequency band.

A strong correlation between seismic noise and independent measurements of human mobility suggests that seismology provides an absolute, real-time estimate of population dynamics.