Wisconsin is situated in an area of relatively low seismic activity. This reduced risk is due to the state’s location deep within the continental interior, far from the boundaries where tectonic plates actively meet and grind against each other. Although significant seismic events are rare, the state occasionally experiences minor tremors that are either locally generated or felt from larger quakes in neighboring states.
Details of Wisconsin’s Most Recent Earthquake
The most recent documented seismic event with an epicenter near the state occurred on August 2, 2024, beneath Lake Michigan. The United States Geological Survey (USGS) recorded the tremor as a magnitude 2.9 event, striking at approximately 9:18 a.m. local time. The epicenter was situated about 25 miles east-southeast of Sturgeon Bay, with a shallow depth of 11.5 kilometers (7 miles) below the lakebed.
This minor earthquake was felt by a small number of residents in coastal communities. Reports submitted to the USGS described a brief, vibrating sensation, often likened to a large truck passing by a home. This was the second recorded tremor in 2024, following a magnitude 2.5 earthquake near Crandon in January.
Historical Context of Seismic Activity
Wisconsin’s seismic history is marked by infrequent, low-to-moderate magnitude events. Most felt tremors originate outside of its borders, often traced back to larger earthquakes centered in neighboring Illinois, Ohio, or Canada. These distant events transmit energy across the stable bedrock of the central United States, causing perceptible motion in cities like Milwaukee.
The largest historical earthquake occurred on May 6, 1947, centered south of Milwaukee in Lake Michigan. Estimated at magnitude 3.8, its effects were widely felt across a 3,000-square-mile area of southeastern Wisconsin, causing minor effects such as broken dishes and building evacuations. More recently, the state experienced a magnitude 1.5 event near Clintonville in 2012, preceded by unusual noises reported by residents.
Underlying Geological Structure
Wisconsin’s low seismic profile is due to its position deep within the North American Craton, the stable, ancient core of the continent. This block of crustal rock is far removed from the active plate boundaries that define higher-risk zones along the Pacific coast. The bedrock beneath the state stabilized billions of years ago.
The region contains ancient features, such as the Midcontinent Rift System (MCRS), a 1.1-billion-year-old failed rift valley extending through the central United States. While the faults related to the MCRS are largely inactive, occasional minor tremors may be attributed to the subtle reactivation of these old zones of weakness under modern stresses. These deep-seated faults accumulate stress very slowly, resulting in rare, small-magnitude earthquakes that register on seismic instruments.