ALBANY, Calif. — Fandom of any kind is all about passion. However, Taylor Swift’s fanbase, playfully nicknamed Swifties, often display levels of devotion to the popular singer that appear to border on obsession. Now, new research finds that Swifties really are a force of nature — at least when they’re at a Taylor Swift concert. Scientists from the Seismological Society of America and Caltech report it was likely the dancing and jumping motions of the audience at SoFi Stadium during an August 2023 Taylor Swift concert that produced the concert’s distinct harmonic tremors.
Simply put, Swifties are literally causing unique seismic activity with each song at the singer’s events.
Previously, researchers speculated that the recorded seismic activity must have originated from the musical beats or reverberations of the sound system. Led by Gabrielle Tepp of Caltech, the new study details how researchers identified the seismic signature of individual songs in order to determine the strength of each song’s tremor.
Study authors also utilized a small amount of data revealing how Swift’s concert stacks up, seismically speaking, against other summer of 2023 SoFi concerts, featuring Beyoncé, Metallica, and Morgan Wallen.
Just a month earlier, seismic activity recorded at a Taylor Swift concert in Seattle prompted the California Office of Emergency Services to ask seismic network operators in the state to figure out if any interesting research could take place during Swift’s August concert dates in Los Angeles. So, Tepp and her colleagues set up a series of strong motion sensors at SoFi Stadium and went on to analyze the data collected by those devices in conjunction with additional data gathered using regional seismic network stations nearby.
Prior studies say that a “concert tremor” is capable of being recorded as long-duration signals featuring narrowband, harmonic frequency peaks anywhere between one and 10 hertz. That variety of low-frequency signal appears similar to a harmonic tremor recorded from natural sources like volcanoes and human sources like trains.
One of the main goals set by the research team was to determine a way to extract the concert’s tremor signals using spectrograms. For reference, spectrograms are graphs that display the strength of various signal frequencies over a certain period of time. In many cases, they display frequencies of sound waves, but they can also assist seismologists in the visualization of signals recorded by seismometers and other instruments.
For Tepp, who has studied volcanoes and also happens to be a musician, the data collected at the concert was a great opportunity to test methods for the detection of seismic signals in spectrograms.
“For earthquakes, most of the time they’re pretty sharp and easy to identify with waveforms, but when you have something like volcanoes where you have such a wide variety of signals, spectrograms can be really handy in helping to identify the different types of signals,” Tepp says in a media release.
Every single Swift song featured a distinct tremor signal. During the August 2023 concert, researchers identified 43 of the 45 songs played within the recorded spectrograms.
Study authors also made it a point to calculate the radiated energy of each song and interpret that figure within the context of the local magnitude of an earthquake that would have radiated the same energy levels. Songs varied significantly in terms of magnitude; “Shake It Off” recorded the largest local magnitude of 0.851.
“Keep in mind this energy was released over a few minutes compared to a second for an earthquake of that size. Based on the maximum strength of shaking, the strongest tremor was equivalent to a magnitude -2 earthquake,” Tepp adds.
So, where did all that harmonic tremor originate from?
“My gut feeling was that if you have a harmonic signal that is nice like these, it had to be from the music or the instruments or something,” Tepp comments.
The research team determined that the best way to explain their collected data was that the movement of the 70,000-plus crowd caused the harmonic tremor. In an attempt to confirm this theory, they put together a few experiments. One entailed playing songs on a portable PA speaker next to a strong motion sensor. Meanwhile, Tepp plugged in her own bass guitar to the speaker and played a simple repetitive beat. She also leaped up and down next to the sensor while rocking out to Swift’s hit song “Love Story.”
The experimental data did in fact confirm that it was the motion, and not the music, that was responsible for creating the harmonic tremor.
“Even though I was not great at staying in the same place—I ended up jumping around in a small circle, like at a concert—I was surprised at how clear the signal came out,” Tepp notes.
Tepp adds she was surprised that the bass beats “didn’t make a harmonic signal, even though they were more accurately on the beat than my jumping.”
The study author speculates this may have more to do with the signal shape (bass beats have a rounder, more emergent shape than the “spike” of a jump) relative to the space between each beat or jump. That relationship may “have implications for why some seismic signals show up as harmonic in spectrograms while other similar ones do not.”
Study authors used data gathered from the regional seismic network stations in order to view the tremors created by the summer’s other headliners at SoFi. Some of the more fascinating data points came from the Metallica concert.
“Other concerts had nice straight-line harmonic signals, but the signals from the Metallica concert were slanted and kind of weird looking,” Tepp says. “We don’t have a great explanation for that yet.”
One possible explanation is that the beat rate for Swift’s songs doesn’t vary much across live and album performances, while Metallica’s beat rates “are all over the map,” Tepp notes. Videos of the concerts also show differences between Swift’s highly choreographed shows and the members of Metallica wandering around the stage.
“The tremor signals themselves are likely coming from the audience, but if the band is varying the beat or speed of songs as they go, maybe the audience is reacting differently,” Tepp suggests.
The Metallica concert also “had the weakest signals in terms of the strongest magnitude from each concert,” the researcher concludes. “Metal fans like to headbang a lot, so they’re not necessarily bouncing. It might just be that the ways in which they move don’t create as strong of a signal.”
The study is published in the journal Seismological Research Letters.