A seismometer is a device that’s usually used to measure earthquakes using vibrations in the earth. But recently, researchers have been using them to measure human movement. A global study published in this week's Science shows that seismic noise is at an all time low, as a result of COVID-19 related lockdowns.
The study takes data from researchers from all over the world. Human activity produces vibrations as we move around, creating “a near-continuous signal especially on seismometers in urban environments.” Human influence on seismometers reflects “a wide variety of activities happening at different times and places at or near the Earth’s surface.” According to the study, the entire world has seen a months-long reduction in seismic noise of 50%, the longest such period on record.
Ben van der Pluijm is a geologist at the University of Michigan. He says anthropogenic noise, or human-produced noise, has always been a component in measuring data from seismometers.
“We’ve always known there’s a significant component of ‘societal noise,’ as I like to call it. But we’ve never had an experiment whereby we could see what it was like without that noise. This gave us an opportunity to see now really, what is the contribution of society on the measurements we have on our equipment, but also allowed us to fine tune what kind of noises we have," he said. "It works both ways, we could also see whether people were actually following the rules.”
Van der Pluijm installed seismometers in Michigan Stadium and in his office building on central campus in Ann Arbor back in 2018. He was able to see the change in noise after Governor Gretchen Whitmer issued her "stay at home order" back in March.
“The unit that’s located in Michigan Stadium only saw maybe about a 30% reduction, whereas the unit that was stationed on Central Campus where buildings were vacated and people were no longer at all moving around saw more than 50% reduction.”
He says the reduction on campus was larger than the stadium probably because Michigan Stadium is located at the intersection of two fairly busy roads.
“We don’t have any units that showed zero noise, by the way. There is always noise. Industry, and there’s always transportation, but a reduction of more than 50% is quite remarkable.”
Van der Pluijm says as lockdown rules are lifted, he has been able to see seismic noise tick back up on his equipment.
“It was a unique situation because we’ve never been able to turn off society.”
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