As Seattle Seahawks running back Marshawn Lynch slipped out of the grasp of the New Orleans Saints last week to make a 67-yard touchdown run, the 66,336 fans in the stadium made their own impressive 100-yard play though they didn't know it at the time. Their cheering and jumping shook the ground enough to register as a small seismic event on a nearby seismometer, part of the Pacific Northwest Seismic Network.
The stadium is listed in the top 10 for providing a home-team advantage. Seahawks fans are known for their game-disrupting audio track, making it difficult for the opposing team to hear the quarterback call the play. But this is the first caught recording of Seahawks causing quake-like disturbances.
Network Director John Vidale caught the action on a seismometer mounted 100 yards from the stadium. Part of the near real-time network of seismometers tracking earthquakes, tectonic, and seismic activity across the Pacific Northwest - the seismometer is strategically placed to monitor the vulnerable Alaskan Way Viaduct. The two-level overpass highway was built in 1953, before earthquake regulations in Seattle were in place. The 6.8 magnitude 2001 Nisqually earthquake damaged the viaduct, and struck during the time the stadium was under construction.
Qwest Field, originally named the Seahawks Stadium, was built intentionally to bounce the noise of the crowd off the partial roof and onto the field. At the same time it had to meet city regulations that demand it be structurally safe enough to withstand the biggest earthquake the region might experience, according to one of its architects James Poulson, design director of Ellerbe Becket in Kansas City. Steel pilings, driven down to bedrock at a depth of 80 to 160 feet deep, prop up the stadium over the soft sediment that was once a tidal marshland, he told Discovery News. "During Seattle's logging days, sawmills shoved the shavings from the logs into the tidal basin so it's not solid fill below surface," Poulson said.
Seattle's soft ground amplified the stadium's crowd stomping and shaking the same way as its roof amplifies the crowd noise, giving the stadium fans their very own seismic profile. Vidale says he will look at the historical record to see if he can correlate past games with the seismic noise.
As reported in the Seattle Times, this event was not the first time seismometers have caught fan action:
Scientists in Cameroon were baffled in 2006 when their seismic network picked up a series of short, simultaneous spikes across the country. It took them a while to realize each jolt represented a goal scored by the national soccer squad in televised games of the African Cup of Nations.
This weekend the Seahawks will play Chicago at Soldier Field. Geophysicist Tim Larson of the Illinois Geological Survey was keen on the idea of monitoring the Chicago fans, but explained that the solid ground under Chicago gave their team a more stable footing. Good luck Bears, but personally I hope the Seahawks give the Seattle fans and Vidale another chance to test the seismometer this season.
IMAGES: Seattle Seahawks running back Marshawn Lynch jumps out of the tackle of New Orleans Saints safety Roman Harper during a 67-yard touchdown run in the second half of a NFC Wild Card playoff game at Qwest Field in Seattle, Washington, USA, 08 January 2011. The Seahawks upset the Saints 41-36. Credit: STEPHEN BRASHEAR/epa/Corbis. Seismic profile courtesy of John Vidale of the Pacific Northwest Seismic Network.