Milwaukee, Wisconsin – A rare Midwest earthquake early Tuesday is now raising awareness across Wisconsin as a powerful blast of Arctic air sends temperatures plunging into extreme territory, creating conditions that could trigger frost quakes during the coldest overnight hours.
According to the U.S. Geological Survey, a 3.5 magnitude earthquake struck central Illinois shortly before 2 a.m. Tuesday, centered about 35 miles south of Springfield. The shallow quake was felt across a wide portion of Illinois, with thousands reporting shaking and loud rumbles before sunrise. While no damage was reported, seismic events of this size are uncommon in the Midwest, making the timing notable as dangerous cold settles across the region.
As the deep freeze grips Wisconsin, geologists say rapid temperature drops can lead to frost quakes, also known as cryoseisms. These occur when moisture in the ground freezes suddenly, causing soil and rock to contract and fracture. The resulting boom or vibration can feel like a small earthquake and may rattle homes, garages, and vehicles, especially overnight.
Central and northern Wisconsin, along with parts of eastern Wisconsin including Milwaukee, Madison, Green Bay, Wausau, and Eau Claire, may be more susceptible as temperatures plunge well below normal following recent snow and moisture. Frost quakes are shallow and localized but can crack pavement, foundations, and underground utilities.
State emergency officials emphasize that frost quakes are not tied to fault lines and do not signal larger earthquakes. Residents are encouraged to remain alert during the coldest hours, inspect property if shaking is felt, and report loud booms or ground movement to local authorities or the USGS. With dangerous cold expected to persist through midweek, additional advisories or alerts may be issued as conditions continue to evolve.
