The probability of a large earthquake occurring in any specific area within a given time frame is based on several variables including recorded historical seismic activity and geologic setting. Given the geologic settings in Alabama and the Southeast, strong magnitude earthquakes are a possibility. Scientists researching the seismic setting in the Southern Appalachians have estimated probabilities of a large magnitude quake occurring with variations in their estimates. According to previous research:
USGS states the East Tennessee Seismic Zone (southern Appalachians) is capable of a 7.5 magnitude event (Wheeler and Frankel, 2000). Recurrence of a 5 – 6 magnitude event has been estimated at once every 200-300 yrs (Bollinger et al., 1989; Chapman, 2000)
For the New Madrid Seismic Zone, according to USGS Fact Sheet 131-02: It is generally accepted that earthquakes can be expected in the future as frequently as in the recent past. Given this assumption, and interpretations of research collected over the past 15 years, USGS* estimates that for the next 50 year period:
The National Hazards Map (right from 2002) is based on earthquake occurrences in areas and on shaking extent relative to the epicenter. Colors show levels of horizontal shaking that have a 1-in-10 chance of being exceeded in a 50-year period. Four zones of frequent earthquake activity affect Alabama (above). They are the New Madrid Seismic Zone, the Southern Appalachian Seismic Zone, the South Carolina Seismic Zone and the Bahamas Fracture Seismic Zone.