It is said that air traffic controllers at O'Hare have nerves of steel. At 4:39 a.m. Friday, the steel was tested as the tower started swaying for about half-a-minute.
"No exaggeration, it was lanky. The tower was swaying," said O'Hare air traffic controller Craig Burzych.
Its brief earthquake dance did not hurt the tower, or air traffic, and it appears not to have hurt other buildings in Chicago, which did their own swaying Friday morning.
"It's highly unlikely that a building would've been affected," said Gene Corley of CTL Group, who is a licensed structural engineer and teaches earthquake science to fellow engineers.
One of Corley's models shows that seismic waves grow longer over distance, which means the taller the building, the more noticeable the sway.
"At the distance we are from where the earthquake occurred, whatever buildings respond, it's not very likely to be damaged because we're far enough away. There's just not a lot of energy left," Corley said.
Therefore, it is not likely that anything was damaged in Chicago from a moderate earthquake 200 miles south of the city. Nonetheless, it pays to be sure. So, city inspectors were out Friday looking at bridges and viaducts, particularly the multi-level structures.
"We've found no damage whatsoever and don't anticipate seeing any problems. But as a precaution, we want to have a set of eyes on it," said Brian Steele of the Chicago Dept. of Transportation.
Chicago buildings are not built with earthquakes in mind, but the tall ones are built to withstand strong winds, another similar horizontal force.
With so many cranes populating the skyline, they and exterior elevators got some immediate attention Friday morning from contractors. The Building Owners and Managers Association (BOMA) says everything looks ok.
"[The city is] recommending that people expect cranes, scaffolding and other vulnerable structural elements just to be safe," said BOMA Executive Director Michael Cornicelli.
Exelon says it has conducted 'walk-downs' of its nuclear plants in Illinois throughout the day and all are running as normal.
Nicor and Peoples Energy say their gas lines are ok, as well.