Scientists now say it's likely that an earthquake shook the Western suburbs after a blast at a McCook quarry on Nov. 4.
According to a report on ABC 7's website, the blast likely triggered what the U.S. Geological survey now believes was a release of tectonic strain.
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"To release the strain basically means that the strain caused fracturing of the earth's crust," scientist Jim Dewey told ABC 7.
Planned quarry blasts don't usually trigger larger follow-up tremors, the report said.