Big drop in Earth’s surface vibrations seen during covid-19 lockdowns

Lockdowns to contain the coronavirus led to drastic reductions in the vibrations of Earth’s surface, as people significantly curtailed their activity.

Seismologists measure vibrations from earthquakes that travel through Earth’s surface. Their instruments also pick up vibrations from noisy human activities, like heavy footfall in crowded pedestrian areas, vehicle traffic, industrial operations and rowdy stadium crowds causing “football quakes”.

A few days after Belgium introduced stay-at-home orders to help contain covid-19 in March, Thomas Lecocq, a seismologist at the Royal Observatory of Belgium, noticed that his instruments were detecting far less noise than normal. He contacted colleagues in other countries and found they were observing similar things.

They analysed records from 268 seismometer stations around the world and found a sudden quietening of seismic noise that began in China in late January, then spread to Europe and the rest of the world in March and April, in line with lockdown implementations.

This makes sense, since most noisy human activities were curtailed during lockdowns, says Kasper van Wijk at the University of Auckland in New Zealand, who was involved in the study. “But we were still surprised by the magnitude of the impact,” he says.

A seismic station in Sri Lanka, for example, recorded a 50 per cent drop in seismic noise after the country enforced strict stay-at-home orders. A station in Barbados recorded a 45 per cent drop and another in New York recorded a 10 per cent drop following lockdowns.

Seismologists have used this unusual quiet period to conduct studies that aren’t normally possible and may assist with earthquake forecasting, says van Wijk. “Basically, we can record cleaner seismic signals from the Earth,” he says.

For example, seismologists have been able to record signals from very weak earthquakes, which are usually drowned out by human noise, says van Wijk. This information could help identify new fault lines that may one day trigger major earthquakes, he says.