Noise created by humans, such as car traffic, quieted by about 30% between late March and early May, 2020, when Governor Greg Abbott closed schools and restaurants across Texas, according to analysis by researchers at Southern Methodist University (SMU).
"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. Arrowsmith and his students looked at data from a dozen seismometers (地震仪) across North Texas. 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, construction and traffic.
The idea of using seismometers to track urban noise gained popularity last 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 enthusiastic response from scientists that he launched the group "Lockdown Seismology" online. "It's where bored seismologists around the world are working together," Arrowsmith joked.
Arrowsmith hopes his findings will contribute to a growing list of creative ways in which researchers are using seismometers. In his course, Arrowsmith teaches students how seismic stations can help investigators solve crimes, like terrorist bombings, aid scientists in tracking nuclear tests or assist inspectors in investigating accidents, like chemical plant explosions. One potential application of his research is to better understand the shallow layers of Earth beneath cities. "That could be useful in places where there's a real seismic hazard (风
险), like San Francisco or Los Angeles," he said, "where just knowing what that shallow structure is tells you a lot about how it would respond in a big earthquake."