Last November, seven seconds after routine blasting, a 3.2 magnitude earthquake felt for miles shook loose ceiling tiles and startled neighbors. Four and a half months later, workers are back in the bowels of the federal stone quarry's 300-million-year old limestone.
On Tuesday, a controlled explosion knocked 18,000 tons of limestone free without a noticeable follow-up tremor.
"We would not be blasting. We would not be blasting today if we didn't think it was safe," Mike Stanczak, Hanson Aggregates, quarry owner, said.
Since the November 4th tremor, the Quarry owners have partnered with Northwestern University and have added more seismographic gear to better read the earth's behavior.
In December, a seismograph was placed deep in the quarry. It is on 24 hours a day, seven days a week. The seismograph is also connected to the National Earthquake Center in Colorado.
As Tuesday's blast occurred, the Northwestern team read two dozen mini seismographs placed in a nearby park to measure seismic waves. That's the beginning of an analysis to see if there is a linkage between the November quarry blast and the quake that followed. Northwestern University Professor Suzan van der Lee thinks there likely is, but there are many variables.
"It's also possible that prior blasts changed the stress so much that the earthquake was bound to happen but this provided an incremental -- tipped it over the edge- tipped it over the edge," Professor van der Lee said.
"We wanna know if there is a correlation because if there is - like I say- we can work around it," Stanczak said.
Researchers will analyze data, but there are no guaranteed answers. However, constant seismograph reading could better pinpoint the epicenter of last November's tremor.
