From travelling to attending live sporting events, everything we do creates seismic noise. All these vibrations from ground motions travel through Earth and are picked up by seismometers. Then COVID-19 happened, and many parts of the world went eerily quiet. A graphic on YouTube shows just how quiet the world got.
A study published in the journal ‘Science’ says this noise fell by up to half during the COVID-19 lockdowns worldwide, making history in the process. “The 2020 seismic noise quiet period is the longest and most prominent global anthropogenic seismic noise reduction on record.” The study involved 76 authors from 66 institutions in 27 countries. Using motion data from 268 monitoring stations in 117 countries, an international team of researchers found that Earth vibrations caused by humans dropped by up to 50 % between March and May this year. “I think one of the most interesting things for me is that this is really our first look at what actually contributes to the human-caused field of noise,” co-author and seismologist Dr Steve Hicks from Imperial College London (UCL) told the ‘BBC’. “And as populations get bigger, and as cities get bigger - particularly those in geologically hazardous areas - we need to work out how we’re going to monitor those hazards, such as earthquakes, volcanoes and landslides. Because as time goes on, more and more important signals that tell us about these kinds of events are going to get concealed.”
The scientists observed a wave of silence as measures were implemented to combat the coronavirus pandemic. “You can almost see it as a wave,” Dr Hicks explained in ‘The Guardian’. “You can see the seismic quietening spread over time, starting in China in late January and then moving on to Italy and beyond in March and April.” The quiet enabled them to listen in in more detail on Earth’s natural vibrations. “The quietening is unprecedented, at least as far as we can go back in time with continuous seismic data,” noted lead author Thomas Lecocq from the Royal Observatory of Belgium that led the study. Dr Hicks continued: “It’s important to see those small signals because it tells you if a geological fault, for example, is releasing its stress in lots of small earthquakes or if it’s silent and the stress is building up over the longer term. It tells you how the fault is behaving.” Of course, the biggest reductions were recorded in densely populated cities like New York City and Singapore. However, declines were also detected in places like Germany’s Black Forest and Rundu in Namibia. In a UCL news release, Dr Hicks concluded: “The lockdowns caused by the coronavirus pandemic may have given us a glimmer of insight into how human and natural noise interacts with the Earth. We hope this insight will spawn new studies that help us listen better to the Earth and understand natural signals we would otherwise have missed.”
COVID-19, coronavirus, noise, vibration, seismic noise, pandemic, lockdown