The Illinois Department of Natural Resources on Wednesday confirmed that there were “two separate seismic events” originating from Chicago’s southwest suburbs on Monday. One of those was related to blasting at the Hanson Material Service quarry at 47th Street and East Avenue in McCook.

The other? According to the IDNR, it’s something of a mystery.

And now the U.S. congressman who represents the area around the quarry wants a federal investigation into the tremor, which violently shook buildings and reportedly could be felt as far away as southern Wisconsin.

U.S. Rep. Dan Lipinski on Wednesday asked the U.S. Department of Labor and the Bureau of Alcohol, Tobacco and Firearms to open formal investigations “into the reported use of explosives at the Hanson Materials quarry in the village of McCook, Ill.”

Lipinski has asked the federal agencies to determine whether any laws were violated regarding “explosive purchase, storage, use and disposal at the site.”

In his letter to the agencies, Lipinski says that residents near the quarry “face daily challenges as a consequence of the quarry, including frequent blasting.”

“An event on the scale of Nov. 4, however, is simply unacceptable in such a populated area,” said Lipinski, who criticized the quarry for its “lack of consultation with local officials, authorities and residents about any increased blasting activity at the quarry.”

What still isn’t known definitively is whether the blasting at the quarry on Monday was actually related to the second, apparently stronger, seismic event several seconds later.

The U.S. Geological Survey, which monitors seismic events, told the Landmark on Tuesday that they recorded just one seismic event and that typical quarry blasting is far too weak to trigger an earthquake.

But both a spokesman for the quarry and the IDNR say there were, indeed, two separate events.

“We have no reason to believe that there is a connection between our routine blast and this seismic event,” said Jeff Sieg, director of communications for Lehigh Hanson Inc., the parent company of Hanson Material Service in a press release issued Tuesday.

IDNR inspector Myron McCaskey visited the Hanson on both Monday and Tuesday in the wake of the tremor.

In his report to the IDNR’s Office of Mines and Minerals, McCaskey states Hanson has four permanent seismographs surrounding the quarry and a portable one that’s placed near the blast site.

On Nov. 4, the seismographs recorded two separate events, one at 12:39 p.m., which was attributed to the blasting, and another one seven seconds later.

“The subsequent event,” McCaskey wrote, “is of unknown origin.”

In a separate press release, the IDNR stated the quarry was “within the statutory limits for blasting and quarry operation, after reviewing the company’s blasting records and blasting measurement readings, which were taken properly.”

As for what caused the second seismic event, IDNR’s Mike Falter, who is chief of the Office of Mines and Minerals’ Blasting and Explosives Unit, said, “What this secondary event was, or what caused it, is outside our regulatory expertise.”

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