The COVID-19 pandemic triggered a period of silence in anthropogenic seismic noise worldwide
A study published in the journal Science by a group of international seismologists, including two scientists from the Institut de Physique du Globe de Paris (University of Paris, CNRS), has shown that containment measures to combat the spread of COVID-19 have led to a 50% reduction in the seismic noise observed worldwide in 2020. Over and above the observation of this unprecedented phenomenon on a global scale, these measures enable us to better characterize the seismic noise due to human activity, and the study thus suggests a new method of monitoring human activities, without the use of personal data.
Publication date: 24/07/2020
General public, Observatories, Press, Research
Related themes : Natural Hazards
By analysing data from more than 300 seismic stations around the world, the study showed that seismic noise has decreased in many countries and regions, making it possible to visualise a ‘wave’ of containment moving through China, then on to Italy and the rest of the world. This seismic quiet shows the full effect of the physical distancing measures taken by the authorities, the reduction in economic and industrial activity and the drop in tourism and travel. This silent period in 2020 is the longest and most significant reduction in anthropogenic seismic noise ever recorded.
This study was initiated by Thomas Lecocq (researcher at the Royal Observatory of Belgium), who decided to share his analysis codes with the entire seismological community. The result is a unique collaboration involving 76 authors from 66 institutions in 27 countries.
At the IPGP, Claudio Satriano and Lise Retailleau contributed by analysing data from the CURIE seismometer, located underground at the IPGP site on rue Cuvier, as well as from other French seismological stations on the islands of Mayotte, La Réunion and Martinique.
Seismometers are scientific instruments capable of detecting vibrations propagating through the ground – known as seismic waves. Traditionally, seismology has focused on measuring the seismic waves caused by earthquakes. However, the recordings of these natural seismic sources are contaminated by the high-frequency vibrations of human activity on the planet’s surface: travel (on foot, by car, by train, etc.) creates unique seismic signatures in the subsoil, while heavy industry and construction work also generate seismic waves that are recorded by seismometers.
For this study, the scientists collected, processed and analysed tens of terabytes of available data. The data comes from thousands of seismic monitoring stations around the world, from state-of-the-art seismic monitoring networks, but also from citizen seismic sensors that individuals and schools have installed on their premises, sharing data with the global community.
By analysing these data, the authors of the study observe that, while the frequency of earthquakes in 2020 remains identical to that of previous years, the drop in man-made noise is unprecedented. The greatest reductions in seismic noise were measured in urban areas, but the study also found signatures of confinement on sensors buried hundreds of metres underground and in less urbanised areas, such as sub-Saharan Africa.
This silent period could even make it possible to detect new types of signals, since seismic signals that are normally masked within the seismic noise, particularly during the day, are much clearer on seismic sensors in urban areas during confinement. The authors of the article hope that this initial work will lead to further studies on these signals, which can be detected during confinement, and the new data they could provide on earthquakes and volcanoes in particular.
The study also showed a strong correlation between the decreases in seismic noise caused by the reduction in human activity and human mobility data obtained from mapping applications on mobile phones and made available to the public by Google and Apple. This correlation should make it possible, in the future, to use seismic data as an indirect indicator of human activity in near-real time and, for example, to measure adherence to pandemic containment measures without having to resort to data posing potential confidentiality problems.
With increasing urbanisation and growing populations worldwide, more people will be living in geologically hazardous areas. As a result, it will become more important than ever to characterise the anthropogenic noise that humans cause so that seismologists can better listen to the Earth, particularly in cities, and monitor the movements of the ground beneath our feet.
The environmental effects of the containment measures linked to the pandemic are many and varied, with reductions in atmospheric emissions, traffic and noise pollution affecting wildlife in particular. This period of time has been named “anthropause”(https://www.nature.com/articles/s41559-020-1237-z) by the scientific community. This new publication is the first global study of the impact of the anthropause on the solid Earth.
Ref: Global quieting of high-frequency seismic noise due to COVID-19 pandemic lockdown measures. Thomas Lecocq, Stephen Hicks, Koen Van Noten, Kasper van Wijk, Paula Koelemeijer, et al, Science, 24 July 2020. DOI: 10.1126/science.abd2438
