Residents of Fairwater, Markesan, Oakfield, Waupun, Campbellsport and Brandon in Fond du Lac County called authorities and posted on social media sites to report a loud cracking sound around 6 p.m. Tuesday that some said shook their homes, the Fond du Lac Reporter said Thursday.
The Fond du Lac County Sheriff's Office said officers investigated the reports, but were unable to identify the source of the sound.
University of Wisconsin, Milwaukee, seismologist Brett Ketter said the sound may have been a cryoseisms, commonly known as a frost quake or ice quake. He said the phenomenon results from water freezing and expanding in the soil and bedrock. The expanding builds pressure that eventually leads to a popping sound that can resemble an earthquake.
"We might hear more of that in the next couple of days as it gets warmer as that frozen water down there starts to melt," Ketter said. "Things might go back to where they were and it might create another pop."