NEW YORK – “I shake it off, I shake it off,” American singer Taylor Swift sang. And boy did her fans deliver.

A Swift concert in downtown Seattle in the United States on July 22 and 23 shook the ground so hard, it registered signals on a nearby seismometer roughly equivalent to a magnitude 2.3 earthquake, seismologists said.

“It’s certainly the biggest concert we’ve had in a while,” said Dr Mouse Reusch, a seismologist at the Pacific Northwest Seismic Network, which monitors earthquake activity in the Pacific Northwest. “We’re talking about 70,000 people and all the music and paraphernalia associated with the concert.”

The so-called Swift Quake recorded a maximum ground acceleration of roughly 0.011 metres per second squared, said Dr Jackie Caplan-Auerbach, a seismologist at Western Washington University.

Seismologists use acceleration to measure ground vibrations, which are then converted to the more conventional Richter scale, the common measurement for earthquakes.

Seismometers can pick up ground vibrations of all types – including from cars and stampeding cattle – but the magnitude of the Swift Quake has drawn comparisons to the professional American football “Beast Quake” of 2011.

That seismic activity was triggered when Seattle Seahawks fans roared in celebration following a last-minute touchdown by Marshawn Lynch, a running back whose nickname is “Beast Mode”.

Dr Reusch said that the activity at the time was close to a magnitude 2.0 earthquake. The Swift Quake was recorded by the same seismic station, located just outside Lumen Field.

The readings occurred throughout both of Swift’s concerts on the nights of July 22 and 23 and was sustained throughout.

The shaking of the ground was more than “twice as hard” as at the 2011 Seahawks game, Dr Caplan-Auerbach said. While this was 0.3 magnitude greater than in 2011, that is a twofold difference under the Richter scale, which is logarithmic.

The likely cause was a combination of the music from the concert’s sound system and Swift’s fans – sometimes known as Swifties – dancing in sync with it, seismologists said.

The pop megastar is four months into her Eras Tour, a sold-out 52-date American tour that has drawn immense crowds of Swifties to hear her perform songs spanning her 10-album career.

The 33-year-old’s opening Arizona show in March drew about 70,000 fans. Ticket prices for her show in Santa Clara, California, last Friday were selling for up to US$20,000 (S$26,600) on Vivid Seats, a second-hand ticket exchange.

The two back-to-back concerts in Seattle logged a near-identical pattern on the seismometer, Dr Reusch said, which suggested the sets were nearly identical as well.

“That was surprising to me, that we’re able to see something so coherent,” she said. “One was offset by about 26 minutes because it was late.”

The shaking at both shows reached a maximum peak twice, first around 7.30pm, and the second around 9.30pm, according to data shared with The New York Times.

It was not immediately clear which Swift songs caused the peaks. Besides Shake It Off, the set list included Love Story, Bad Blood and Anti-Hero, all songs guaranteed to get Swifties on their feet.

While the concerts shook the ground exceptionally hard, Dr Caplan-Auerback said, it is important to understand that seismometers pick up signals from “anything that shakes the ground”, including cars, trains and even wind.

Nor are Swift’s earthshaking abilities unique to the music world.

The seismometer also recorded signals when Canadian singer The Weeknd played at Lumen Field on Aug 25, 2022, Dr Caplan-Auerback said, though they were not as strong.

American pop star Beyonce will be playing there on Sept 14, she said. “I’ll be looking at that for sure.”

As for Dr Reusch, she was encouraged by the public attention.

“Maybe there’s some young Swifties out there that will some day become seismologists or earth scientists,” she said. “That would be a real happy ending.” NYTIMES