A unique collaboration involving 76 authors, 66 institutions, 27 countries and many citizen scientists has published the first global study of 2020’s “anthropause.”
While humans may not be enjoying the COVID-19 lockdown very much, the environment is faring a little better. Reduced air and light pollution, less atmospheric emissions, reduced human interference on wildlife and more have led researchers to coin this unprecedented time period the “anthropause.”
And now, further evidence is available—a new collaborative study has found a 50 percent reduction in seismic noise worldwide from March to May of this year. While the results are destined for the history books, they will also play a huge role in optimizing future seismic monitoring, as this was the first study to detect previously concealed earthquake signals.
Normally, seismographs cannot detect small earthquakes, especially in urban areas, as extensive vibrations generated from human sources, such as cars, trains, construction equipment and even walking, skew the recordings. As these study results show, that has not been the case for 2020 thus far, opening a new, previously unattainable avenue of exploration for seismologists.
For the study, the research team compiled a global seismic noise dataset from 337 global seismometer stations, generating useable data from 268 stations. Lockdown effects were observed at 185 out of the 268 stations. Interesting, visualizing the findings results in a “wave” that starts in China in January, moves to Europe in March, and continues to spread to the United States and the rest of the world in late-March and April.
For example, researchers recorded a 50 percent reduction in seismic noise in Sri Lanka immediately following lockdown protocol—the strongest observed reduction from that permanent station since at least July 2013. In Central Park, New York, on Sunday nights, noise was 10 percent lower during the lockdown compared with before it. A permanent seismic station in New Zealand experienced a 50 percent reduction, but when lockdown restrictions were lifted on April 27, 2020, the island’s noise increased almost immediately to pre-lockdown levels.
“The length and quiescence of [March to May 2020] represents the longest and most coherent global seismic noise reduction in recorded history, highlighting how human activities impact the solid Earth,” the researchers write in their study, recently published in Science.
Beyond record-setting noise reduction, the low-noise period has important implications on the future of seismology research.
Using a service station in Brussels, Belgium that experienced a 33 percent reduction in noise after lockdown, the researchers compared data from a nearby microphone that records audible traffic noise and independent mobility data. Unsurprisingly, they found a strong match between seismic noise reductions and publicly available human mobility datasets from mapping apps on cellphones. This correlation allows open seismic data to be used as a broad proxy for tracking human activity in near real-time, and can help further understand the effects of pandemic lockdowns and recoveries without potential privacy issues.
“The 2020 seismic quiet period is a baseline for using seismic properties to identify and isolate the sources contributing to the anthropogenic noise wavefield, especially when combined with data indicative of human behavior,” the researchers write. “The seismic observations of human activity during the COVID-19 lockdown allow us to assess the impact of mitigation policies on daily life, especially the time to establish and recover from lockdowns.”
When the researchers recorded a M5.0 earthquake near Petatlan, Mexico during lockdown, it became the first published evidence that low-level earthquake signals, especially during the daytime, were likely being drowned out in urban areas under normal circumstances. Of course, lockdown is anything but normal and the resulting nearly 40 percent reduction in noise made the event easily visible at a station in Querétaro City 236 miles away.
“Low noise levels during COVID-19 lockdowns could thus allow detection of signals from new sources in areas with incomplete seismic catalogs. Such newly identified signals could be used as distinct templates for finding similar waveforms in noisier data pre- and post-lockdown,” the research team concluded.