The U.S. Geological Survey says the shaking with a measured magnitude 3.2 in northern Illinois was a blast and not an earthquake.
USGS geophysicist Don Blakeman also says it appears Monday afternoon's blast came from within a rock quarry but that the exact location of the blast had not yet been determined. He says that all indications so far leads experts to believe that the blast came from the quarry. That includes that the epicenter is in an area close to the quarry.
Originally, the USGS said the shaking was an earthquake but the agency soon determined it was a blast.
The blast shook various communities southwest of Chicago, including Indian Head Park and Countryside. There were no immediate reports of damage or injuries.
