The Excitement of 70,000 Swifties Can Shake the Earth

The Economist reports: "Shake, shake, shake, shake," Taylor Swift sings from the stage of Lumen Field in Seattle at 10.35 in the evening on July 22nd. The fans respond, enthusiastically; the stadium duly shakes; a nearby seismometer takes note. To pop aficionados "Shake it off" is an empowering up-tempo anthem played at 160 beats per minute. To the Pacific Northwest Seismic Network, which is designed to monitor earthquakes, it is a 2.6 hertz signal in which the amplitude of the acceleration was as large as one centimetre per second, per second. The well-situated seismometer first came to public attention in January 2011, when it recorded the response of fans of the Seattle Seahawks, an American football team, to a magnificent touchdown by Marshawn Lynch, a running back known as "Beast Mode." The "Beast Quake" went down in local sporting history. When Ms Swift came to town for two nights of her Eras tour, Jacqueline Caplan-Auerbach, a geology professor at Western Washington University, used the opportunity to learn more about how events in the stadium shake its surroundings. On December 11th she presented some of her conclusions at the American Geophysical Union's autumn meeting in San Francisco. [...] Dr Caplan-Auerbach wanted to see whether such resonant amplification might also be at play elsewhere, and to distinguish between the effect of the music itself and the audience's response. Her concert-night data showed two distinct sets of signals, one in higher frequencies (30-80hz), one in lower frequencies (1-8hz). The higher-frequency signals were present during the sound check, when the band were on stage but the stadium empty, and absent during the concerts' "surprise songs," played without the band by Ms Swift alone. The lower frequencies were absent when the audience had yet to arrive. Clearly those higher frequencies were from the music itself.

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