Something that marks how strange times are, was that in March and April, a group of seismologists found seismic activity fell by 50% at 185 stations around the world (at least in certain high frequency bands from 4 – 14 Hz). For example the three graphs below show seismic activity in Brussels, Barbados and New Zealand. A slight downturn happens at Christmas but the lockdown period fell far below that.
For the first time seismologists could identify small quake signals they had missed before.
Co-author Dr Stephen Hicks, from Imperial’s Department of Earth Science and Engineering, said: “This quiet period is likely the longest and largest dampening of human-caused seismic noise since we started monitoring the Earth in detail using vast monitoring networks of seismometers.
Who knows what they might figure out now they have a handle on human background “noise”.
(B) Lockdown effects in hiFSAN compared with audible environmental noise and independent mobility data in Brussels, Belgium. (C) Lockdown effect in Barbados compared to noise levels in the last decade (in gray) and correlation with local flight data at the Grantley Adams International Airport (TBPB) (24). (D) Lockdown noise reduction recorded on borehole seismometers in Auckland, New Zealand. (Click to enlarge).
For the record, there will be an array of other frequencies that aren’t listed here because they didn’t change much.
It’s just a bit of Covid trivia, but as an opportunity for experiments, 2020 is surely a researchers dream.
For the technically inclined:
We assessed the effects of COVID-19 lockdowns on high-Frequency (4–14 Hz) Seismic Ambient Noise (hiFSAN; (24)). We compiled a global seismic noise dataset using vertical-component seismic waveform data from 337 broadband and individually operated citizen seismometer stations (24), such as Raspberry Shakes (RS), with a self-noise well below the ground motion generated by anthropogenic noise (25), and flat responses in the target frequency band (Fig. 1). For 268 seismic stations, we obtained usable data (e.g., no large data gaps, working sensors) and found significant reductions in hiFSAN during local lockdown measures at 185 stations (Fig. 2). Periods that are often seismically quiet include weekends, and the Christmas / New Year holidays for those locations where these are celebrated. We found a near-global reduction in noise, commencing in China in late Jan 2020, then followed by Europe and the rest of the world in Mar to Apr 2020. The noise level we observe during lockdowns lasted longer and was often quieter than the Christmas to New Year period.
REFERENCE
T. Lecocq et al.(2020). Global quieting of high-frequency seismic noise due to COVID-19 pandemic lockdown measures,, Science, 10.1126/science.abd2438