The U.S. Geological Survey now says a quarry blast shook northern Illinois at a magnitude 3.7.
The agency said earlier Monday afternoon that the rumbles were an earthquake. Later, the USGS updated its report to say the shaking was a quarry blast in the southwestern Chicago suburb of Countryside.
The agency says the shaking struck Indian Head Park in Cook County around 12:35 p.m. It was about 1.4 kilometers deep.
Indian Head Park is about 16 miles southwest of Chicago and has about 3,800 residents.
There were no immediate reports of damage or injuries.