COVID-19 pandemic causes seismic noise quiet period in 2020 | WPN World People News

Seismic noise is measure by seismometers. These are sensitive scientific instruments to record vibrations travelling through the ground – known as seismic waves. Traditionally, seismology focuses on measuring seismic waves arising after earthquakes. Seismic records from natural sources however are contaminated by high-frequency vibrations (“buzz”) from humans at the surface – walking around, driving cars, public transport, heavy industry and construction work all create unique seismic signatures in the subsurface that are recorded on seismometers. The buzz is stronger during the day than at night and weaker on weekends than weekdays.

THE YEAR OF SILENCE

By comparing lockdown seismic noise to months-to-years long datasets from over 300 seismic stations around the world, the study was able to show the seismic noise reduced in many countries and regions, making it possible to visualise the resulting “wave” moving through China, then to Italy, and around the rest of the world. The seismic lockdown sees the total effect of physical/social distancing measures, reduced economic and industrial activity and drops in tourism and travel. The 2020 seismic noise quiet period is the longest and most prominent global anthropogenic seismic noise reduction on record.

While 2020 has not seen a reduction in earthquakes, the drop in the anthropogenic “buzz” has been unprecedented. The strongest seismic noise reductions were found in urban areas, but the study also found signatures of the lockdown on sensors buried hundreds of metres into the ground. Not only in densely populated areas, but also in more remote areas, such as in Sub-Saharan Africa, a noise reduction was observed.

The study found a strong match between seismic noise reductions and human mobility datasets drawn from mapping apps on mobile phones and made publicly available by Google and Apple. This correlation allows open seismic data to be used as a broad proxy for tracking human activity in near-real-time, and to understand the effects of pandemic lockdowns and recoveries without impinging on potential privacy issues.

The environmental effects of the pandemic lockdowns are wide and varied, including reduced emissions in the atmosphere and reduced traffic and noise pollution impacting wildlife. This period of time has been coined “anthropause”. This new study is the first global study of the impact of the anthropause on the solid Earth beneath our feet.

BELGIAN INITIATIVE

The study was spawned after the lead author, seismologist Dr. Thomas Lecocq of the Royal Observatory of Belgium, decided that the best way to tackle the problem of analysing data from all around the globe was to share his method with the seismological community. This started a unique collaboration involving 76 authors from 66 institutions in 27 countries.

There are many thousands of seismic monitoring stations around the world, and it took a team effort to download, process, and analyse the many terabytes of data available. Data came from high-end seismic monitoring networks, as well as citizen seismic sensors which individuals and schools have installed themselves, sharing data to a global community.

Seismologists Thomas Lecocq and Koen Van Noten of the Royal Observatory of Belgium led this study. The seismometer data of the Uccle station UCCS was at the origin of the study. They contributed by including seismometer data of the Belgian national seismic network in the study. Benoît Fauville of Brussels Environment participated with audible data from microphones installed in Brussels. The sound drop in the audible data during lockdown (i.e. a quieter city) correlated with the noise drop.

IMPORTANCE OF THE STUDY

Will the 2020 seismic noise quiet period allow new types of signals to be detected? The study has shown the first evidence that previously concealed earthquake signals, especially during daytime, appeared much clearer on seismic sensors in urban areas during lockdown. The study’s authors hope that their work will spawn further research on the seismic lockdown. Finding previously hidden signals from earthquakes and volcanoes will be one key aim.

With growing urbanisation and increasing populations globally, more people will be living in geologically hazardous areas. Therefore it will become more important than ever to characterise the anthropogenic noise humans cause so that seismologists can better listen to the Earth, especially in cities, and monitor the ground movements beneath our feet.

Source: Royal Observatory of Belgium