A few days back, a tremor shook the city of Lima. Although far from being one that caused any kind of damage at all, it registered on the Sismo Detector app, software that alerts Peruvians that a potentially dangerous earthquake may be occurring.

Peru is a very seismically active part of the world, so a mild quake or two is nothing to be concerned or even surprised about. Remarkably though, this particular tremor wasn’t caused by any sort of geological process: it was triggered by soccer fans, all celebrating a decisive Peruvian goal over New Zealand during the 2018 World Cup qualifiers.

The game was being played Lima’s National Stadium, and pretty much all of the city’s residents were watching closely. It turns out to have been a pretty important match, as victory would ensure that, for the first time since 1982, Peru would have been permitted to play in the World Cup.

Twenty-seven minutes into the match, Peru’s Jefferson Farfan broke the 0-0 stalemate with what apparently was a rather marvelous goal. This set off a wave of jump-based ecstasy in Lima, which literally shook the ground.

This, along with the enormous amounts of people jumping up and down in people’s homes, registered as a seismic tremor on accelerometers belonging to the Geophysical Institute of Peru (IGP) in numerous districts. An initial wave was apparently caused by the city-wide jumpers, with a second following closely afterwards thanks to the prolonged jubilation of those in the stadium itself.

While technically not an earthquake – no faults were moved – it registered as a 1.0M tremor. It was sudden and widespread enough to trigger the Sismo Detector app to send out an alert.

Later, Sismologia Chile, a Twitter account that’s linked to the Sismo Detector app, said: “Incredible!” adding that “The emotion of the Peruvians made the application activate.”

The creator of Sismo Detector, Professor Francesco Finazzi of the University of Bergamo in Italy, thinks that the alert was generated in error. The simultaneous movement of all the people within their homes caused the little accelerometer inside everyone’s smartphones to shake at the same time, which looks like a natural earthquake to the system.

However, the president of the IGP Hernando Tavera also confirmed there was “a vibration propagated by the ground caused by the euphoric jumps in unison of some fifty thousand people who attended the National Stadium.” This, in turn, registered as a seismic wave on the IGP’s own accelerometers, although Finazzi tells IFLScience that the IGP probably detected "local noise rather than a propagating seismic wave."

Either way, this isn’t the first time happy stadium-based fans have generated significant seismic waves. Back in 2011, the Foo Fighters were playing in Auckland, New Zealand. During the gig, the 50,000 fans managed to cause tremors that local seismographs thought were being generated by volcanic activity.