Blasting at the Hanson Material Service quarry at 47th Street and East Avenue in McCook is reportedly responsible for what was at first believed to be an earthquake whose epicenter was located in the southwest suburbs.

Shortly after noon on Monday, the U.S. Geological Survey observed what was first reported as seismic activity that registered 3.7 on the Richter scale. It was later reduced to 3.2 and the USGS attributed the event to quarry blasting.

Vulcan Materials Company, which operates a large quarry near 55th Street and Joliet Avenue, stated it did not do any blasting on Monday, according to Brookfield Village Manager Riccardo Ginex, who said he had that message from a Vulcan official.

A message left by the Landmark at Hanson Material Service went unanswered, but Countryside City Administrator Gail Paul said she received confirmation from someone at the company that blasting had occurred there around noon.

“I did get hold of a woman at Hanson and asked if they had blasted 10 minutes earlier, and she did say yes,” said Paul, who called the company shortly after feeling the Countryside City Hall shake violently. “The city hall shook for an extended period of time.”

Paul said she asked the Hanson employee if the blast had exceeded requirements set by the Illinois Department of Natural Resources, and that the employee responded “she was not able to give me any information.”

According to Paul, she instructed the company to get back to her with an explanation of what occurred. As of 5 p.m. Monday, no one had called her back.

The Countryside City Hall sits across East Avenue from the Hanson quarry and workers at city hall are used to blasting, which happens several times a week, according to Paul. But on Monday, as Paul sat in her office, she felt her chair shake and described the blast as much louder and much longer than usual.

“I was on the phone and told the person that I had to go, because either a semi had hit the building or we were about to fall into the quarry across the street,” Paul said. “Our phone was ringing off the hook.”

In addition to calls asking what the shaking was all about, Paul said the city did seven inspections of industrial buildings near the quarry after their owners complained the buildings had suffered structural damage from the blast.

“We felt some strong blasts earlier in the year but nothing felt like this,” Paul said.

According to news reports, the effects of the blast could be felt as far away as Chicago and Naperville.

At Brookfield Village Hall, Deputy Clerk Theresa Coady was at her desk when the blast occurred.

“It was just weird,” said Coady. “It felt like those sonic booms we felt in grade school. The windows were shaking.”