Media release
From: University of Auckland From: Victoria University of Wellington**Press Release from the University of Auckland**
The quiet Earth
As many daily activities came to a halt during lockdown, the Earth itself became quiet, probably quieter than it has been since humans developed the technology to listen in.
Seismologists have analysed datasets from more than 300 international seismic stations – including several located in New Zealand - and found the “buzz” of human activity, called anthropogenic noise, dropped dramatically.
Scientists have dubbed it the ‘anthropause’ because it’s the longest and most prominent anthropogenic noise reduction on record. It was detected not just in cities but in some of the planet’s most remote places including sub-Saharan Africa.
In New Zealand, seismologist Dr Kasper van Wijk from the University of Auckland was busy looking at seismic data from the tragic eruption at Whakaari/While Island and wasn’t really thinking about lockdown until colleague Dr Thomas Lecocq of the Royal Observatory of Belgium got in touch.
“I used the computer code for White Island to analyse Auckland’s seismic data, and to my surprise, within an hour I could confirm that Auckland was not only quiet above ground but also underground,” he says.
Traditionally, measuring seismic waves is focused on detecting earthquakes and volcanic activity but because seismographs are so sensitive, they can also pick up vibrations from humans at the surface as we walk around, drive cars and catch a train. Heavy industry and construction work also generate seismic noise.
New Zealand’s strict lockdown measures meant a lack of anthropogenic seismic noise was detected at places like Eden Park where a seismograph is buried 380m beneath the sports grounds, and even on Motutapu Island in the Hauraki Gulf.
Because it is situated on a volcanic field, Auckland is a key focus for seismologists – there are 12 seismographs in and around the city monitoring even the weakest signs of earthquakes or volcanic unrest.
The study already presented an example in Mexico, where an earthquake recording appeared much clearer on seismic sensors when humans were confined to quarters. The project’s leaders, including Dr van Wijk, hope their work will help improve our ability to detect these previously hidden signals.
“One day a volcano in Auckland’s volcanic field will erupt but it will create seismic signals before that happens and this study reminds us that if humans made less noise, we would get an earlier warning,” Dr van Wijk says.
Findings from the study are published in Science and show a 50 per cent reduction in seismic noise on seismographs around the world from early- to mid-2020. Lead authors were based in New Zealand, Belgium, the United Kingdom and Mexico and overall 76 scientists from 27 countries were involved.
There are thousands of international seismic monitoring stations, some run by enthusiastic amateurs including students. Dr van Wijk heads the Ru Network of Seismometers in Schools programme which has seen dozens of seismographs installed in schools that, while not as powerful as professional seismic stations, detect earthquakes. At St Mary’s School in Rotorua the days of lockdown were quieter than even any day during the summer school holidays.
The study found a strong match between seismic noise reductions and human mobility data from mapping apps on mobile phones, made available by Google and Apple. This correlation allows open seismic data to be used as a broad proxy for tracking human activity in near-real-time, and to understand the effects of pandemic lockdowns and recoveries without impinging on potential privacy issues, Dr Lecocq says.
It is also the first evidence that previously concealed earthquake signals, especially during daytime, are much clearer on seismic sensors with reduced anthropogenic noise and the researchers hope this will help detect previously hidden signals from earthquakes and volcanoes.
**Press Release from Victoria University of Wellington**
Quiet time across the world
You may have noticed New Zealand was significantly quieter during the COVID-19 lockdown. The noise from cars, emergency sirens, and children playing in the school yard faded away, leaving urban areas in particular much less noisy during March and April 2020.
Now an international study involving Professor Martha Savage from Te Herenga Waka—Victoria University of Wellington’s School of Geography, Environment, and Earth Sciences has shown there was also a significant measurable reduction in seismic noise. With lockdown measures limiting social, physical, economic, industrial, and tourism-related movement, observed seismic noise reduced by 50 percent across the world.
“Seismic noise is the low level buzz of noise caused by humans moving around on the ground,” Professor Savage says. “Everything from walking to driving to construction can cause this buzz.
“The difference was most noticeable in urban areas, but this reduction in noise was observable at even the most remote locations the research team was able to observe, in Sub-Saharan Africa,” Professor Savage says. “This quiet period is the longest and most prominent seismic noise reduction on record.”
Seismic noise, or the lack of it, can be measured on seismometers, equipment that is normally installed in the ground to measure geological activity from earthquakes and volcanoes. For this study, the team—76 researchers from 66 institutions in 27 countries led by Dr Thomas Lecocq of the Royal Observatory of Belgium—used 300 seismometers around the world to record their data. Each researcher used the same methods and equipment to collect data, collaborating remotely using online tools while they were all stuck at home during lockdown. Professor Savage and Associate Professor Kasper van Wijk from the University of Auckland were the only New Zealand researchers involved in the project.
With such a large team working together, the researchers were able to visualise a ‘wave’ of quiet moving around the world from China to Italy and then on to the rest of the world as different areas went into lockdown. They used the seismic noise measurements in combination with anonymised data from Google and Apple Maps that showed human movement.
“We were able to clearly link reductions in activity with lower seismic noise readings,” Professor Savage says.
“This is exciting for future research, as it gives us a way to broadly track human activity in near real-time without affecting people’s privacy, as we don’t need to track specific people or sources of noise. This could be used now to track the effects of pandemics and the recovery from COVID-19 and how it has impacted human activity.”
The study could also contribute to geological research, Professor Savage says.
“Earthquake signals can often be concealed or obscured by seismic noise, but they appeared much more clearly on the seismometers during lockdown. This data could be used to find new insights about earthquake activity and volcanic activity, particularly in urban areas.”
The initial findings from the research were published in the journal Science this week. Professor Savage says additional papers will also provide further insight into changes in noise in specific locations.
