Yes, Illinois experiences earthquakes, though the state is not located on a tectonic plate boundary like California or Alaska. These seismic events are considered intraplate earthquakes because they occur within the interior of the North American continental plate. While most tremors are too small to be noticed, the region has a history of major seismic activity, which presents a unique risk. Understanding the underlying geology and specific fault zones is necessary to grasp this hazard.
The Source: Ancient Faults and Intraplate Activity
Earthquakes in the central United States, including Illinois, result from ancient, pre-existing zones of weakness within the continental crust. These zones are remnants of past geological episodes, such as the failed Reelfoot Rift system, which fractured and weakened the crust. Deep faults created during this rifting are now buried under layers of rock and sediment.
The driving force that reactivates these old faults is the current tectonic stress from the slow, continuous movement of the North American Plate. As the plate moves, it transmits compressional and tensional forces across the Illinois region. When stress builds up sufficiently along a buried zone of weakness, the fault slips, releasing energy as an earthquake.
This mechanism explains why seismic waves in the central and eastern U.S. travel farther and cause shaking over a wider area than similar earthquakes in plate-boundary regions. The hard, dense bedrock of the continental interior allows seismic energy to propagate with less dampening. Consequently, a moderate earthquake in Illinois can be felt across more than a dozen states.
Major Seismic Zones Affecting Illinois
Illinois is threatened by two major seismic zones in the central U.S., both capable of producing significant damage. The most widely known is the New Madrid Seismic Zone (NMSZ), a 150-mile-long fault system extending through Arkansas, Missouri, Kentucky, and into southern Illinois. During the winter of 1811–1812, the NMSZ produced a sequence of three massive earthquakes, estimated between magnitude 7 and 8, felt across the entire eastern half of the country.
The NMSZ poses a risk to Southern and Central Illinois. There is a current probability estimated at 25% to 40% for a magnitude 6.0 or greater earthquake to occur within a 50-year period. A large-scale event could cause severe damage, especially due to the potential for soil liquefaction across the Mississippi River Valley, which is a process where saturated soil temporarily loses strength and behaves like a liquid.
The second significant threat is the Wabash Valley Seismic Zone (WVSZ), centered along the border between southeastern Illinois and southwestern Indiana. This active intraplate region is capable of generating earthquakes up to magnitude 7.0. The WVSZ affects Illinois population centers more directly than the NMSZ, including communities such as Mount Carmel.
Evidence from paleoseismology, the study of prehistoric earthquakes, shows that the lower Wabash Valley has experienced multiple large quakes, potentially magnitude 6.7 or greater. The most recent notable event was a magnitude 5.2 earthquake near Mount Carmel, Illinois, in 2008. This quake was felt in at least 16 states and caused minor structural damage near the epicenter.
Historical Context and Frequency
While the potential for a major earthquake exists, the vast majority of seismic activity in Illinois is minor and imperceptible. The state experiences, on average, about one felt earthquake per year, with most events registering below magnitude 3.0. Since the mid-20th century, instrumental monitoring has recorded over a thousand tremors, but only a small fraction have been strong enough to be noticed.
Significantly larger events, those exceeding magnitude 5.0, occur infrequently, roughly every few decades. The 2008 Mount Carmel earthquake and a magnitude 5.4 quake in 1968 near Dale, Illinois, represent the type of moderate, damaging event that can occur within the state’s borders. These events, though rare, demonstrate the ongoing seismic hazard.
The historical record also includes the New Madrid sequence of 1811–1812, which highlights the possibility of extremely rare, high-magnitude events that can recur every 700 to 1,200 years. Today, seismic activity is continuously monitored by networks, including those operated by the U.S. Geological Survey and state geological surveys. This monitoring provides scientists with data to better understand stress accumulation and recurrence intervals in the central U.S.