Since late Thursday, March 29, Clintonville has four seismometers located in and around the city.
The events that have been occurring for the past two weeks are confirmed in one case and believed in other cases to be swarms of small earthquakes.
City Administrator Lisa Kuss explained in a press release distributed Monday, April 2, that the smaller the event and the further away the seismometers are from it, the more difficult it is to record the events.
“On Thursday, March 29 at around 8:10 p.m., just a short time after the fourth seismometer was installed, the Police Dispatch Center received five calls that loud booms were felt and heard,” said Kuss. “At this time the data from the seismometers was being collected but not yet being fed live to the USGS. This 8:10 p.m. event was recorded on all four meters.”
Greg Waite, assistant professor at Michigan Technological University, reviewed the data and was able to confirm that a very small earthquake did occur at that time. Waite is not normally one to officially determine earthquakes for the public.
“I would estimate the magnitude at 0.1, based on the duration of the signal. The depth was around 1 km (about 0.5 miles), although there is some uncertainty in the depth estimate. There is a big difference between a M1.5 (from March 20) and M0.1. The M1.5 releases about 125 times more energy than a M0.1. This explains why these very small events are not detected on the stations 20 km (12 miles) or more away and can only be seen with the newly installed network in Clintonville,” Waite said.
“The City is very grateful to Professor Waite and Graduate Students Kathleen McKee and Josh Richardson for their efforts to install these seismometers so that the City will be more likely to capture these small events,” said Kuss. “City officials would like to again emphasize that the only way to find these small events is when we receive calls from citizens that heard or felt the event. The USGS staff will not receive an automatic notice of events if they continue to be very small. The staff will need to look for the events based on reports from citizens. If no calls come in there will be no times to ask to have reviewed. Calls should be placed to the Police Department at 715-823-3117.”