The United States Geological Society (USGS) recently changed the designation of the tremor felt throughout the western suburbs on Nov. 4 – as well as a similar event from Aug. 31, 2010 – from quarry blast to earthquake after careful review of the data from seismic monitoring equipment.
Now the question remains: Did blasting at the quarry trigger the earthquake?
No one knows for sure. In a summary prepared by Lehigh Hanson's (the company that was blasting at the quarry on Nov. 4) explosive contractor, Alexander Tyson from Dyno Nobel, he wrote:
“While there are some human activities like waste water injection in the earth, deep gold mining, or coal mine collapses that have been strongly linked to seismic activity, there has never been a proven case of surface quarry blasting like this triggering an earthquake. The rock upon which this area sits is very unique ... it’s also the site of an ancient meteorite impact that left a group of faults called the Des Plaines Disturbance. The fact that these faults are so much nearer to the surface than typical faults means that earthquakes along them may be triggered by human-created or natural conditions that have never before been considered by seismologists.”
It is clear that more information is needed in order to determine if the quarry blast triggered the earthquake, and if so, what Hanson can do to prevent this from happening again.
Currently, the following is underway:
• Hanson is notifying everyone who reported damages that their damage inspection consultant, VibraTech, will be calling them to set up an appointment.
• Hanson will notify all communities before resuming blasting operations.
• Hanson and the USGS are considering setting up a USGS monitoring station at the quarry. Hanson contacted experts at Northwestern University’s Technical Institute. They have expressed interest in studying the seismic activity and geology of the area.
• Congressman Dan Lipinski continues to speak with the director of the U.S. Department of Labor and the Illinois Department of Natural Resources. The Congressman reported to me, “ … I continue to work with state and federal regulators and with Hanson Materials to understand exactly what happened and why. USGS now says that an earthquake occurred, but they believe that it was likely caused by normal, legal activities at the quarry. There are still many questions left unanswered. I have had many productive discussions with all stakeholders involved and will continue to do so until we get some of these questions answered. I am committed to making sure that we do everything possible to prevent such an event from happening again.”
The Lyons Township Quarry Advisory Council (LTQAC) will meet again in December to review the progress.
Gail Paul is city administrator and LTQAC chairman for the city of Countryside