Seattle is one of the most seismically active cities in the United States, and when the city's beloved NFL team plays (particularly in the playoffs), the ground actually vibrates thanks to their roaring, stomping, and dancing fans. 

It's one of the reasons why a group of seismologists have deployed three earthquake monitoring instruments at CenturyLink stadium. 

The Pacific Northwest Seismic Network (PNSN) - a joint operation between the University of Washington and the University of Oregon - is usually focused on detecting earthquakes and volcanic activity in the region. 

But on Sundays in January - over the past two seasons anyway - football comes first. (And perhaps its excusable, so long as by watching and monitoring the games, geologists can learn something about earthquake readiness). 

The Seattle Seahawks are the defending National Football League champions and are one win away from returning to the Super Bowl for a second consecutive year. But the team's most important player (arguably) isn't on the field, but in the stands. 

The crowd at CenturyLink field in Seattle has acquired a reputation around the league as being one of the loudest, and rowdiest in the country, and has earned the moniker: the 12th man (gridiron football only allows 11 players on the field, per squad, at a given time). 

John Vidale, director of the PNSN, told ScienceAlert that the organisation became interested in measuring ground movement (however minimal) during Seahawks' games after fan celebrations following a 2011 touchdown registered on a nearby seismogram, down the road from the stadium. 

The play Vidale is referring to - which has been dubbed the "Beast Quake" touchdown - was this extraordinary score by running back Marshaun Lynch, who broke nine tackles, and ran nearly 70 yards into the endzone.

According to WIRED's Nick Stockton, "the stomping and jumping from crazed fans was so intense that it lit up a nearby seismometer. At its peak, the so-called 'Beast Quake' shook the sensor about 1/100th of a millimetre, with an acceleration of about 1/20,000th of Earth's gravity." 

Last Sunday, when the Seahawks played host to the Carolina Panthers, the PNSN created a website called QuickShake where fans were able to see how much the stadium was shaking at any given moment. (The website will be live again this Sunday, when Seattle takes on Green Bay). 

"It's hard to simulate thousands of people using this tool all at once. When we can get a lot of people looking, we can see problems that we'd encounter during an actual earthquake," Vidale said in a press release

During last week's game there was an interception that led to a 90-yard return for a touchdown. It was a big play for the defending champs, and according to the PNSN blog it did create some vibrations, but it didn't quite stack up to Beast Quake. 

While the vibrations are unlikely to spur any real seismic activity, they are expected to help the PNSN with the development of an early warning system, which it is working on with the US Geological Survey. 

Vidale says its "mostly an exercise in rapidly putting out instruments, educating the public, and testing whether our software and web page can deliver information quickly to large numbers of observers." 

Still, Vidale told ScienceAlert they have learned they can "show ground motions within two to three seconds" of when they happen, which is "much faster" than they were able to before. 

"Two situations in which [ground motion detection] speed matters are watching for volcanoes and large aftershocks, when people sometimes would like to get out of harm's way quickly," he told ScienceAlert. "If we issue an earthquake early warning - that an earthquake has started and strong shaking is likely to be incoming soon - people would like some visual confirmation that the alert was not a false alarm." 

Vidale also weighed in on his pick for Sunday's game, and predictably he's got the Seahawks beating the Green Bay Packers 35 to 14. 

Source: WIRED