The Pacific Northwest Seismic Network began to notice geophysical anomalies in the south end of the city of Seattle on Sunday afternoons not long after the NFL Seahawks opened their new stadium in 2002. These were recorded by spectrograms and seismograms that rated frequency content and envelope function and the fascinating sort of things that seismologists like to discuss at cocktail parties, but the bottom line was that the ground was shaking.

It isn't enough to open the Cascadia fault, or threaten to dump the city into Puget Sound, but on many occasions the roar of nearly 70,000 fans and the attendant shaking of the stadium itself is more than enough to unnerve visiting football teams. When the Eagles play Sunday afternoon in CenturyLink Field, they will have three opponents: a taxing cross-country trip, a very good football team, and a 12th-man factor provided by the Seahawks' traditionally rabid crowd and a tall, narrow, partially roofed stadium that keeps most of the noise inside.

"It's real," said Eagles coach Doug Pederson, who is from nearby Ferndale, Wash., and attended Seahawks games in the old Kingdome, which was also pretty loud. "I've experienced it firsthand from a fan's perspective as a kid in high school. The way that [newer] stadium is designed and built with that cover right there, everything is kind of right on top of you and it's a great atmosphere."

Oh, sure. It's a great atmosphere if you also enjoy having a conversation near a jet engine. In recent years, CenturyLink Field and Kansas City's Arrowhead Stadium have traded back and forth the title of world's loudest outdoor stadium, as judged by the Guinness Book of World Records. Kansas City is currently in the lead, with a reading of 142.2 decibels, just ahead of Seattle's 137.6, the previous record. As points of comparison, OSHA begins monitoring job safety at 90 decibels and the pain threshold for an average human is reached at 125 decibels, which equates to standing 100 feet from that typical revving jet engine. So, in a word, it will be loud.

"It's deafening, to be honest," said Eagles linebacker Steve Tulloch, who played there in previous stops with Tennessee and Detroit. "You can't hear the guy next to you."

This is particularly important when the guy next to you, or two or three down the line from you, is the quarterback and it would be nice to know exactly when the next play will begin. Road teams in CenturyLink Field annually compile the most false-start and delay-of-game penalties in the NFL and the Eagles took to their sound-infused bubble for two days last week to work on silent count snaps.

"It's loud, and if you give them a chance to cheer, they'll be even louder," tight end Brent Celek said. "The key for us is to try to quiet them a bit. In the huddle, get real close together so everyone's on the same page and make sure we don't have those mistakes. The crowd feeds off those mistakes."

Quieting the crowd would involve taking control of the game, and that's no easy task. Since 2012, when the Seahawks really got it going under coach Pete Carroll, they are 31-5 at home in the regular season and 4-0 in the postseason. That's compared with 21-15-1 on the road and 2-2 in the postseason - not bad but nothing remarkable.

There is a school of thought that while CenturyLink Field is loud and can shake on occasion, there aren't really any quiet NFL stadiums when the home team is rocking. The advantage, if any, comes from the caliber of opponent waiting for you in those stadiums, and, to some extent on how far you have to travel to get there.

"We're about as far away as you can get, so it is a big trip," Carroll said.

The closest NFL opponent is the San Francisco 49ers, who are 840 miles and a two-hour plane ride away in Santa Clara, Calif. Seattle's three division rivals, the 49ers, Rams, and Cardinals, must travel a combined 3,200 miles to get there. By comparison, the Eagles' three NFC East opponents are about 1,600 miles away, almost all of that Dallas.

"You don't make it bigger than it is," said Eagles safety Chris Maragos, who played three seasons with the Seahawks. "It's a loud place, but we play in a lot of loud stadiums. You see teams doing things with crowd noise and hyping it up all week, but it's not like it's a new environment."

That's one way to look at it - or listen to it - and probably a smart approach. We'll see if the Eagles can keep that mind-set when their offense needs to convert a long third down and the decibel meter spikes and the squiggly lines on the seismograph begin to jump and the tackles take their eyes off the defensive line to peer toward the center and anticipate the snap of the ball.

"You can't get enough work on that," said rookie right tackle Halapoulivaati Vaitai.

They tried, though. So have other teams. Recently, trying hasn't been enough in CenturyLink Field.