Residents reported hearing a routine blast at a quarry operated by Hanson Materials in McCook around 12:30 p.m. Monday. It was followed by a much stronger rumble that felt like an earthquake. The U.S. Geological Survey originally classified it as magnitude 3.7 earthquake but later downgraded the intensity.
Investigators with the Illinois Department of Natural Resources' Office of Mines and Minerals completed a two-day on site inspection at the quarry. After reviewing records and equipment, they found the quarry operated within the statutory limits for blasting.
"Our review of quarry records does show measurement equipment picked up vibrations from a second and separate event approximately seven seconds after the initial blast," said DNR's blasting and explosives unit chief Mike Falter. "What this secondary event was, or what caused it, is outside our regulatory expertise."
"I was in my office, doing some paperwork, next thing I know, I hear a big bang. Whole floor shook. I went outside to see if somebody hit my building," Mario Licitra, Licitra Roofing Company, said.
"One guy yelled, 'I think a semi hit the building!'" John Licitra, Licitra Roofing Company, said. "Everyone runs outside."
No one was injured. People from the western suburbs and as far north as Kenosha felt the blast.
Blasting at a quarry is loud and jarring, but for those who live close by, relatively routine. But Monday was different - there were two.
"Like ten seconds later, there was a huge blast and my house was shaking like crazy," said Vijay Parikh, Countryside resident.
Monday's tremor knocked ceiling tiles loose from the ceiling of a hot dog joint in Countryside and rattled a bank in La Grange enough that the manager closed it early.
"At this time we have no reason to believe there is a connection between our routine blast and the seismic event," Hanson Materials said in a statement.
"We can argue over what came first, the chicken or the egg, but there's got to be a reasonable explanation of why those two things occurred at the time they did," said Jeff Tobolski, McCook mayor.
"This was the worst blast in 38 years," said Linda Lauterbach, La Grange resident.
Lauterbach became so concerned about the blasting at the McCook quarry next door, she began keeping a log in June. She says blast patterns have changed but the quarry hasn't offered an explanation.
"They need to figure out why we are hearing these, why we are feeling these so much more and make some adjustments," said Lauterbach.
Julie Dutton, a seismologist with USGS, said only one seismic event was recorded- the blast. "We see the blast," she said. "No earthquake is detected."
"They are acknowledging that there was an event," Tobolski said of the quarry. "And that that event was within the defined parameters of their permit."
Tobolski said the village has no standing over the quarries, which fall under the jurisdiction of the DNR and Illinois Department of Natural Resources (IDNR).
3.2 magnitude felt miles away
The USGS originally reported the incident as a 3.7 magnitude earthquake with an epicenter of Indian Head Park, but later changed the website to say it was a quarry blast with a 3.2 magnitude seismic activity. Whatever the source of the shaking, it was certainly felt.
"It was really quick. The ground kind of like moved a little. I didn't think much of it. I was busy, working... Then I heard something from some people that something had happened, and I thought, 'I felt that,'" Alana Patchak said.
"We ran out of the building. And not only were we outside of the building, we saw people at the post office and also the plumbing building behind us. Everybody's checking their building, making sure everything's OK," Deputy Chief Mark Wodka, Hinsdale Police Department, said.
Residents in the west suburbs felt the shaking around 12:35 p.m. The tremors were classified as "light to weak" according to the earthquake.usg.gov shake map.
Check out the USGS ShakeMap.
ABC7 Facebook fan Pat Kyce-Fisher, who lives in Hodgkins, Ill., wrote, "our mobile home shook about 10-15 minutes ago."
Fan Pam Anderson said she lived by a quarry in Dolton for 20 years but "never recall a blast big enough to register as a possible earthquake."