‘Bored’ seismologists find a new hobby: Tracking silence
DALLAS — If you’ve been noticing more birds chirping and more frogs singing, it’s probably not your imagination.
Noise created by humans, such as car and truck traffic, quieted by about 30 percent between late March, when Gov. Greg Abbott closed schools and restaurants across Texas, and early May, according to a new analysis by researchers at Southern Methodist University.
“There was quite a big change in some areas,” said Stephen Arrowsmith, a seismologist at SMU, who took on the project with a class of undergraduate and graduate students this spring.
Arrowsmith and his students looked at data from a dozen seismometers across North Texas, including in Irving, Dallas, Farmers Branch, Richardson and Fort Worth. Seismometers are used to detect earthquakes, but they are sensitive to just about everything that makes the ground vibrate, such as strong winds, ocean waves, passing trains, construction and traffic.
Each instrument contains a small weight on a spring. As the earth moves, the weight remains in place, allowing the seismometer to measure the amount of movement relative to the weight.
Scientists usually avoid placing seismometers in cities, because the racket of human activity makes earthquake signals hard to detect. But North Texas is an exception.
Scientists at SMU and at the University of Texas at Austin’s Bureau of Economic Geology placed seismometers in the DallasFort Worth area after Texas experienced a surge of small to moderate-sized quakes beginning in 2013. The stations are now part of the state-wide TexNet seismic monitoring program. Researchers linked the North Texas quakes, which peaked in 2015 before dying down, to oil and gas activity.
Arrowsmith and his students saw a range of noise reductions at the various stations. The biggest changes, perhaps not surprisingly, occurred on college campuses. At the University of Texas at Dallas’ campus in Richardson, a TexNet seismic station registered students’ comings and goings as classes started and ended each weekday.
“After the shutdown, that totally disappears, and the background noise goes way down,” said Arrowsmith.
Stations in Irving also registered significant noise reductions, mostly likely due to fewer cars and trucks on the roads, he said.
A seismic station at a firehouse near Farmers Branch, though, registered no change in noise levels, presumably because first responders have remained active throughout the pandemic.
“Each station is telling you about quite local things that are going on near that station,” Arrowsmith said. “So you need a good network of stations to fully understand what the effect of the shutdown is on a city as a whole.”
The idea of using seismometers to track urban noise gained popularity in March when Belgian seismologist Thomas Lecocq posted some of his urban noise data from Brussels on Twitter.
Lecocq, of the Royal Observatory of Belgium, received such an overwhelming response from scientists that he launched the group “Lockdown Seismology” on the Slack communications platform. “It’s where bored seismologists around the world are collaborating,” Arrowsmith joked.