IOLA - The U.S. Geological Survey on Saturday confirmed that earthquakes shook northwest Waupaca County on at least two occasions earlier this month.
The quakes occurred about 7½ miles north of Iola. There were no reports of damage to buildings.
"They're not common in central Wisconsin, but they are out there," said Eric Halverson, deputy director of Waupaca County Emergency Management.
Authorities received reports last week from residents in the area who heard rumbling noises and noticed buildings shaking.
The U.S. Geological Survey identified a 1.3 magnitude earthquake that occurred at 2:35 p.m. July 7 and a 1.5 magnitude earthquake that occurred at 1:39 a.m. July 15.
The quakes occurred at a depth of less than 5 km.
"They're estimating that these were fairly shallow," Halverson told USA TODAY NETWORK-Wisconsin. "Deeper ones that are small, with a magnitude of less than 2, are difficult to hear."
Additional earthquakes were reported but may have been too small for the U.S. Geological Survey to detect. The seismometers used by the agency aren't located nearby.
Halverson said the U.S. Geological Survey will continue to investigate reports of earthquakes in the area.
"They're going to check to see if they can get a portable seismograph to move into the area to see if there's more activity that they're not (currently) able to pick up," Halverson said.
The last confirmed earthquake in Waupaca County occurred on March 20, 2012, near Clintonville. It had a magnitude of 1.5 and was linked to a series of mysterious booms that rattled the city for days.
Clintonville capitalized on the seismic activity by selling T-shirts that said, "I Survived the 1.5."
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