Alabama experiences earthquakes, though they are infrequent and register at low magnitudes. The state is situated within the North American tectonic plate, where seismic stress causes occasional movement along ancient fault lines. While most tremors go unfelt, the state has recorded a history of noticeable seismic activity, meaning the potential for an earthquake remains a measurable hazard.
The Historical Record of Alabama Earthquakes
Seismic data indicates that Alabama has experienced more than 150 earthquakes of magnitude 3.0 or higher since the year 1900. Most of these events have been minor, falling within the magnitude 3.0 to 4.0 range. Only a few are strong enough to be widely felt across the state each year.
The largest known earthquake to originate within Alabama was the estimated magnitude 5.1 Irondale event in October 1916. This moderate quake caused minor damage, such as cracked windows and fallen chimneys, primarily in the Shelby and Jefferson counties near the epicenter. More recently, the state recorded a magnitude 4.9 earthquake near Fort Payne in DeKalb County in 2003, which was felt across 13 states and caused damage to weaker masonry structures and chimneys.
The 4.9 magnitude quake in Escambia County in 1997 was the second largest recorded by seismographs in the state. Historically, the most active area is the Southern Appalachian Seismic Zone, which extends through the northeastern and central parts of the state.
Geological Causes of Seismic Activity
Alabama’s earthquakes are classified as intraplate seismicity, meaning they happen within the interior of the North American tectonic plate, far from plate boundaries. These tremors originate from stress accumulating deep within the continental crust’s basement rock. This stress reactivates ancient faults that have been dormant for millions of years.
The state’s seismic activity is primarily influenced by the Eastern Tennessee Seismic Zone (ETSZ), which extends southwestward from Virginia into central Alabama. The ETSZ is responsible for the region’s persistent, low-level seismicity. Earthquakes in this zone are caused by crustal compression that slowly reactivates deep, historical faults.
A more distant, yet significant, threat is the New Madrid Seismic Zone (NMSZ), located in the Mississippi Valley. A major earthquake there, similar to the 1811–1812 sequence, would cause substantial shaking and potential damage in northern Alabama due to the efficient transmission of seismic energy. Localized seismicity, such as the 1997 Escambia County event, has also led to investigation into whether human activities like oil and gas extraction may have induced movement on pre-existing faults.
Preparedness and Risk Assessment
The earthquake hazard is classified as low, with only a small chance of experiencing damaging ground shaking in any 50-year period. However, the presence of active seismic zones means preparedness is a prudent measure. The risk profile is elevated by the potential for a large, distant event in the New Madrid Seismic Zone to impact the state.
A fundamental safety measure is the practice of “Drop, Cover, and Hold On” during shaking. This action involves immediately dropping to the ground, taking cover under a sturdy piece of furniture, and holding on until the shaking stops. Finding safe spots in each room of a home, such as under a desk or table, can significantly reduce the risk of injury from falling objects.
Residents should assemble a basic emergency kit containing supplies for at least three days, including water, non-perishable food, and a first-aid kit. Securing important documents and finding safe evacuation routes are also recommended steps.