Coronavirus lockdowns around the globe have decreased the amount of seismic noise in Earth’s crust, according to seismologists. Human-induced vibrations are caused by traffic, factories and industrial activities, scientists say that a reduction in seismic noise of this magnitude is usually observed around Christmas.

Coronavirus lockdown and its impact on seismicity

As of today coronavirus (COVID-19) pandemic has caused 1.2 million infections globally and more than 64,000 deaths. Coronavirus lockdowns around the world have brought the lives and economies to a halt. Meanwhile, seismologists have observed a decrease in seismic noise – the hum of vibrations in the planet’s crust, which could be a direct result of reduced industrial and transport-related activities. This reduction in ambient seismic noise could help seismometers in detecting small-scaled earthquakes and boost efforts to monitor volcanic, tsunami and tectonic activities.

“A noise reduction of this magnitude is usually only experienced briefly around Christmas,” said Thomas Lecocq, a seismologist at the Royal Observatory of Belgium. Natural seismic events like earthquakes cause the Earth’s outer layer “crust” to move, so do human-induced activities like vehicles and industrial machinery. Human activities generate vibrations that distort seismic measurements from fine-tuned seismometers. Although effects from individual sources might be small, collectively they produce background noise, which decreases the ability of seismologists to detect other signals occurring at the same frequency.

In Brussels, Belgium a seismic observatory showed that anthropogenic seismic noise fell to about one-third due to coronavirus lockdown measures taken by the Government. “Coronavirus lockdown measures included the closure of restaurants, schools, and other public venues from 14 March, and banning all non-essential travel from 18 March,” according to Dr. Lecocq. The current drop has increased the sensitivity of the observatory’s seismic equipment, improving its ability to detect waves in the same high-frequency range as the noise. The surface seismometer is now almost as sensitive to small seismic events as a counterpart detector buried 100-metre below the Earth’s surface, Dr. Lecocq adds. “This is really getting quiet now in Belgium.”

Seismologists from Belgium are not the only ones to notice the effects of coronavirus lockdown on the Earth’s crust. Dr Stephen Hicks, a seismologist at Imperial College London, tweeted that coronavirus lockdown in the UK has also reduced the amount of seismic noise due to a decrease in the amount of traffic and vehicles. Celeste Labedz, a Ph.D. student in geophysics at the Caltech, tweeted that a similar fall in noise had been picked up by a station in Los Angeles. “The drop is seriously wild,” she said.

However, not all seismic monitoring stations will observe the same results as ones observed in Belgium. As many stations are deliberately located in remote areas or deep boreholes to avoid human noise. These areas would record only smaller decreases, or no decrease at all, in the level of high-frequency noise seismometers usually record.

Boost in earthquake detection

“If coronavirus lockdowns continue in the coming months, seismometers located in urban areas around the world might perform better than usual in the detection of earthquake aftershocks,” says Andy Frassetto, a seismologist at the IRIS, Washington DC.

The decrease in noise could also help seismologists who study naturally occurring background vibrations, such as those from crashing ocean waves, to investigate the Earth’s crust. As volcanism and change in groundwater levels affect how these seismic waves travel, seismologists can observe these events by monitoring the time it takes a wave to reach a given seismometer. A decrease in human activity due to coronavirus lockdown has boosted the performance of seismometers, as scientists like Dr. Lecocq are trying to gain full advantage of this situation to investigate natural seismic waves at similar frequencies. “There’s a big chance indeed it could lead to better measurements,” he says.

Seismology is not the only scientific discipline that has observed changes due to the recent worldwide coronavirus lockdown. Air pollution has also decreased due to coronavirus lockdown, a recent example could be quoted for China, where a decrease in air pollutants in troposphere was observed due to quarantine measures.

Meteorologist Dr. Marshall Shepherd reported that infrasound, which is noise below the frequency of human hearing (less than 20Hz) but in this case not seismic noise, has also decreased. Shepherd’s colleague, John Trostel said that coronavirus lockdown is presenting an opportunity to study infrared sound.”One common example of the reduction in infrasound was from a local wind tunnel research facility, as the facility temporarily closed down, so did the infrasound,” said Trostel. This decrease in infrared sound can help in better detection of weather phenomena like storms.


STORY

Coronavirus lockdowns have changed the way Earth moves
Elizabeth Gibney, Nature (news) | March 31, 2020

CITE THIS ARTICLE: "Coronavirus lockdowns have reduced the Earth’s vibrations," in Geoscience Daily, April 5, 2020, https://geosciencedaily.com/earth/coronavirus-lockdowns-earth-vibrations/.