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A drop in seismic noise from humans could help scientists track volcanic tremors in places like Auckland, New Zealand. Credit: Wikipedia/DXR, CC BY-SA 3.0

Seismic noise has dropped by half during coronavirus lockdown measures, giving scientists a rare lull to search for hidden signals usually drowned out by human activities.

Researchers measure seismic waves coming from natural sources, like earthquakes and volcanoes, as well as human activities. Trucks, cars, factories, and even shopping can create high-frequency seismic waves radiating out from population centers, and most scientists filter out human noise to seek for natural signals.

But seismic noise has been unusually quiet lately, in what scientists are calling the “anthropause.”

“If it’s quieter now and we can pick up some of the smaller signals, that improves our seismic risk analyses,” said Paula Koelemeijer, a lead author on a study published today in the journal Science.

Tracking smaller earthquakes can help scientists understand larger, more dangerous quakes and monitor how faults move. When a magnitude 5.0 earthquake struck Petatlán, Mexico, on 4 July, a station 380 kilometers away was able to detect the quake from raw data. Normally, the station would have missed the small quake without filtering out noise.

“This is likely to become a landmark article in the fields of seismic monitoring and ambient noise tomography,” said volcanologist Jan Lindsay at the University of Auckland who was not involved in the study. “The ‘2020 seismic noise quiet period’ will likely become something that Earth science students of the future will learn about in textbooks.”

Globally, seismic noise dropped by a median average of 50% during the coronavirus lockdowns from March through May. The measurement includes all seismic signals, but scientists attribute the drop to human activity by comparing changes in seismic noise with mobility data from Google and Apple.

The drop in noise varied by location: It decreased by 33% in Brussels, Belgium; 50% in Sri Lanka; and 10% in Central Park, New York. Rural areas grew quieter too—noise at a station at Rundu, Namibia, dropped by over 25%. (Koelemeijer attributed the drop to fewer tourists at a popular hippo-watching spot nearby.) The study pulled data from 185 seismic stations across the globe in both urban and rural locales…

“This study impressively demonstrates just how much man-made noise there actually is,” said research associate Carolin Böse at the GFZ German Research Centre for Geosciences who was not involved in the research. “Seismologists around the world now have a chance to make good use of the data presented in this study and hunt for otherwise ‘hidden signals’ in the seismic recordings.”…

Taking advantage of the “anthropause,” scientists are listening for faint natural signals during the quiet of coronavirus lockdowns: “The Seismic Hush of the Coronavirus.”

* K. C. Cole

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As we celebrate (relative) silence, we might recall that one of the primary man-made sources of seismic “sound” got a boost on this date in 1870: America’s first asphalt pavement was laid in front of City Hall in Newark, N.J.  Edmund J. DeSmedt, the Belgian chemist who oversaw the work, had received a U.S. patent for this asphalt paving method two months earlier.  Later that year, DeSmedt became the inspector of asphalt and cements for the District of Columbia, and oversaw wide application there.

DeSmedt’s crews at work in D.C. in 1876

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