Earthquakes are typically associated with the edges of tectonic plates, but seismic activity is a documented reality even in the stable continental interior of the United States. Ohio, located squarely within the North American Plate, experiences tremors that challenge the common perception of a seismically quiet region. While the state does not face the constant threat of large-magnitude quakes seen on the West Coast, Ohio has a history of felt earthquakes that are an ongoing subject of geological study. This activity is infrequent and low to moderate in size, yet it represents a consistent geological phenomenon.
The Confirmed Reality of Ohio Seismicity
Ohio is an intraplate region, meaning its seismic activity occurs far from the boundaries where Earth’s major tectonic plates meet. These earthquakes are shallow-focus events, originating in the upper crust at depths of about 3 to 6 miles in the crystalline basement rock. The majority of events recorded have been small, with magnitudes falling between 2.0 and 5.0, often felt only locally. Since 1776, the state has been the epicenter for at least 200 earthquakes measuring magnitude 2.0 or greater.
Geological Causes of Intraplate Earthquakes
The underlying mechanism for Ohio’s earthquakes is the slow, continuous build-up of stress within the North American continental plate. This massive landmass is subjected to large-scale, uniform east-west horizontal compression, primarily driven by the movement of tectonic plates and forces like “ridge push.” This stress concentrates on pre-existing zones of weakness within the crust, causing them to fail and slip.
These zones of weakness are ancient faults, deeply buried and poorly mapped, located in the billion-year-old Precambrian basement rock. They were created during past geological events, such as continental rifting and mountain-building episodes. Movement along these dormant, reactivated faults releases the built-up strain energy, resulting in an earthquake. A localized factor is the potential for human-induced seismicity, where the deep injection of fluids from hydraulic fracturing can lubricate or pressurize these faults, triggering smaller events.
Historical Frequency and Major Seismic Zones
The historical record of Ohio seismicity reveals an infrequent but notable pattern of activity. The western part of the state, particularly the Anna Seismic Zone in Shelby County, has historically been the most active area. This zone has experienced over 40 felt earthquakes since 1875, with a recurrence of moderately damaging quakes every few decades. The largest known earthquake with an epicenter in Ohio occurred here on March 9, 1937, registering magnitude 5.4, which caused significant damage and structural failure in the town of Anna.
Northeastern Ohio, specifically the area around Lake and Geauga Counties, is another documented region of activity, with over 100 felt earthquakes since 1836. The largest event in this area was a magnitude 5.0 earthquake in 1986, which caused minor to moderate damage and was felt across 10 states and parts of Canada. Southeastern Ohio has also recorded at least 25 earthquakes above magnitude 2.0 since 1776. Ohio occasionally feels the effects of major regional events, such as the distant New Madrid earthquakes of 1811–1812, which were powerful enough to topple chimneys in Cincinnati.
Assessing Seismic Hazard and Risk
Evaluating the seismic hazard in Ohio is difficult because the recurrence interval for large earthquakes can span hundreds or even thousands of years. The overall hazard is classified as low to moderate, but the potential for damage from a moderate event is higher than in plate boundary regions. This increased risk is due to the nature of the crust in the eastern United States, where brittle and flat-lying rocks transmit seismic wave energy much farther. A moderate eastern U.S. earthquake can result in a damage area approximately ten times larger than a similar event in California.
This assessment informs public safety measures, including the development of building codes that require structures to withstand certain ground motions. The Ohio Seismic Network (OhioSeis) continuously monitors activity to better understand the state’s deep fault systems and refine the risk models. While the probability of a major earthquake remains low, the potential for moderate events means that seismic risk is a necessary consideration for long-term planning and infrastructure design.