INDIAN HEAD PARK, Ill. (AP) -- The U.S. Geological Survey says it appears the shaking in northern Illinois that measured magnitude 3.2 was a quarry blast and not an earthquake.
The USGS originally said an earthquake shook the suburb of Countryside southwest of Chicago on Monday afternoon. But now the agency says there are strong indications it was a quarry blast -- starting with the fact that the epicenter is in an area near a quarry.
Geophysicist Paul Caruso says the "wave patterns" on the equipment that measures seismic events look more like an explosion than an earthquake. But he says there remains some doubt because the rumblings were felt in a large area and not just close to the quarry.
There were no immediate reports of damage or injuries.