Since 1890, Pasadena, California, has celebrated New Year’s Day with the Tournament of Roses, kicked off by the Rose Parade. Earlier this year, as horses, marching bands and flower-covered floats trekked down Colorado Boulevard, scientific research was happening right beneath their feet.
As the parade travelled down the route, fiber optic cables thinner than a human hair measured the way the ground shifted under its weight, Katherine Kornei reports for Science magazine. The results, published on May 6 in Seismological Research Letters, were gathered to calibrate the system so that it can later measure seismic activity like earthquakes.
The cables were originally installed for telecommunications, but lay inactive, or dark. When turned on, “suddenly, you have tens of thousands of sensors,” Zhongwen Zhan, a seismologist at the California Institute of Technology, tells Science magazine. “All you need to do is get permission to connect one instrument.”
The cable that Zhan used to judge marching bands’ volume is part of the Pasadena Array, set up by CalTech last November to measure earthquakes in the city and map the geological structure underneath.
“The Rose Parade, as a well-controlled event—no other traffic except the parade, traveling all in one direction at almost constant speed—provides a rare opportunity for network calibration,” Zhan explains in a statement. According to the university, the two 23-mile-long fiber optic cables provide the equivalent of 30,000 seismic sensors in a city that only has 11 traditional sensors.
To measure the seismic activity of the parade, the researchers pulsed near-infrared lasers through the cables. About once every few feet, there’s a slight imperfection in the light’s path, and the light reflects off of it onto a sensor. When the ground shifts around the cable, the imperfections move and the signal changes. That allowed the researchers to measure seismic activity that moved the fiber as little as a few nanometers.
The fiber optic cables are so sensitive, they could distinguish the seismically loudest marching band in the parade. The ground-shaking honor goes to Southern University and A&M College's marching band—dubbed the "Human Jukebox"—from Baton Rouge, Louisiana, followed by Pasadena City College, Rancho Verde High School, Dobyns Bennett High School and the Los Angeles Unified School District bands, Ken Martinson reports for Marching.com.
The data gathered by the cables even show six minutes of seismic quiet caused when the "Mrs. Meyer's Clean Day" float got stuck at the corner of Colorado and Sierra Madre boulevards, according to the statement.
The idea of sensing vibrations with the movement of fiber optic cables originates in the 1980s, where it was invented for the military, per Science. But the applications are now expanding to anything that might be even the tiniest bit Earth-shaking. Last March, researchers working near Sacramento, California used repurposed dark cables to measure earthquakes in the region for seven months. Like the Pasadena Array intends to do, the Sacramento team used ambient seismic activity—in their case, from trains—to map the ground underneath, Rice University geophysicist Jonathan Ajo-Franklin told Kimberly Cartier at Eos last year.
The precise seismic measuring technique could have applications beyond earthquakes, too. Ajo-Franklin told Eos that the cables could be used to study a range of subsurface geology and the melting of ice sheets. And Zhan tells Science that the cables could pinpoint the location of anything moving nearby, so it could be used to record traffic patterns, identify leaking pipelines, and sense trespassers trying to dig under a barrier.
"We plan to keep the seismic array operational over the next few years, so we plan to do the same for future Rose Parades,” Zhan told Marching.com. “Hopefully with more information about the bands and even some outreach activities."