They've dubbed it the "anthropause" – a quiet interlude when Covid-19-induced lockdowns around the planet hushed the noisy buzz of human activity.
And that lull – measured from Auckland's Eden Park all the way to sub-Saharan Africa – could now point scientists to previously hidden quake activity.
In a study published today, international seismologists, including the University of Auckland's Dr Kasper van Wijk, analysed datasets from 300 stations to find that observed seismic noise dropped away by about 50 per cent across the world.
Amid the lockdown period, Van Wijk was investigating seismic data from December's tragic eruption at Whakaari/White Island when Dr Thomas Lecocq, a scientist at 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," Van Wijk said.
New Zealand wasn't the only quiet spot.
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," said Victoria University professor of geophysics Martha Savage, also a co-author on the paper.
"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."
Usually, 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 construct buildings.
New Zealand's strict lockdown measures meant a lack of human 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 straddled a volcanic field, Auckland was already key focus for seismologists.
Today, there around 12 seismographs located in and around the city that listen for even the weakest signs of earthquakes or volcanic unrest.
During lockdown, the seismic signal of an earthquake in Mexico appeared clearer than normal as humans were confined to quarters.
The project leaders, including 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," he said.
The study has been published in the journal Science.