Michigan is not widely known for seismic activity, yet the state does experience earthquakes. These events are infrequent and typically low in magnitude, resulting in a low seismic risk compared to coastal areas. The tremors occur due to complex forces acting upon the ancient bedrock beneath the surface. Understanding the state’s geological history helps explain why the ground occasionally shakes, even though it is far removed from the nearest tectonic plate boundary.
Historical Record and Frequency
The majority of seismic events centered within Michigan are minor, often registering below magnitude 3.0, making them undetectable to most residents. The state’s strongest recorded earthquake occurred on August 10, 1947, near Coldwater, reaching a magnitude of 4.6. That event caused slight structural damage, including downed chimneys and cracked plaster. A more recent notable quake happened on May 2, 2015, near Galesburg, registering a magnitude of 4.2 and was widely felt across southern Michigan. Historically, a powerful event in 1905 on the Keweenaw Peninsula was estimated to be between magnitude 5.0 and 5.9. Residents occasionally feel the effects of distant, larger earthquakes, such as those originating from the New Madrid Seismic Zone or from eastern Canada.
The Geological Explanation
Michigan experiences earthquakes due to intraplate seismicity, which describes seismic activity far from the edges of tectonic plates. Michigan sits within the North American Craton, a massive, stable block of continental crust. The quakes are caused by the accumulation of stress transmitted across the continent from distant boundaries where the North American Plate interacts with other plates. This immense compressive stress reactivates ancient fault lines deep within the crust. One such zone of weakness is the Midcontinent Rift System (MCR), a 1.1-billion-year-old failed continental split that runs beneath the state. Even though the MCR is no longer actively rifting, its deep-seated fault structures can slip when the continental stress field builds to a breaking point. These faults are typically buried beneath thousands of feet of younger sedimentary rock and glacial deposits, meaning they are not visible at the surface. The slow, ongoing process of post-glacial rebound, where the crust rises after the ice sheets melted away, adds additional strain to these buried zones of weakness.
Seismic Risk and Preparedness
The United States Geological Survey (USGS) National Seismic Hazard Model rates Michigan as having a “Very Low” to “Lowest” seismic risk. This indicates a very small probability of the state experiencing potentially damaging ground shaking in a 50-year period. Michigan consistently ranks among the lowest states nationally for annualized earthquake loss, suggesting that the likelihood of a major, destructive event remains remote. Despite the low risk, awareness of basic safety procedures is prudent for all residents. The primary protocol recommended by emergency management agencies is “Drop, Cover, and Hold On.” This involves dropping to the hands and knees immediately, covering the head and neck beneath a sturdy piece of furniture, and holding onto the shelter until the shaking completely stops. Preparing for an earthquake also involves securing heavy items in the home, such as strapping tall furniture and water heaters to the wall studs to prevent them from toppling over. Establishing a family communication and evacuation plan for any emergency is a sensible step.