The Eastern Tennessee Seismic Zone and Area Faults

Eastern Tennessee Seismic Zone

Alabama sits on the edge of the Eastern Tennessee seismic zone, which extends from south west Virginia to north east Alabama, is one of the most active earthquake areas in the Southeast.

Although the zone has not had a large earthquake in historic times, a few earthquakes have caused slight damage. The largest recorded earthquake in this seismic zone was a magnitude 4.6 that occurred in 1973 near Knoxville.

Sensitive seismographs have recorded hundreds of earthquakes too small to be felt in this seismic zone. Small, non-damaging, felt earthquakes occur about once a year.

Earthquakes in the central and eastern U.S., although less frequent, are typically felt over a much broader region than the western U.S. East of the Rockies, an earthquake can be felt in an area as much as ten times greater than a similar magnitude earthquake on the west coast.

 For example, a magnitude 4.0 eastern U.S. earthquake typically can be felt at many locations as far as 100 km (60 mi) from where it occurred, and it might or might not cause damage near its source.

A magnitude 5.5 eastern US earthquake usually can be felt as far as 500 km (300 mi) in most directions and can cause damage out to 40 km (25 mi).


At plate boundaries, earthquakes can commonly be related to specific faults or fault systems. In contrast, in the eastern Tennessee seismic zone the relation between faults and earthquakes is more enigmatic.
 The Eastern U.S. is far from the plate boundaries, the nearest of which are in the center of the Atlantic Ocean and in the Caribbean Sea. No active faults are known to reach the surface in the region, although the area is laced with ancient faults that developed as the Appalachian Mountains formed several hundred million years ago.
The larger faults, particularly those that have been exposed at the Earth's surface by erosion, are likely to have been mapped by geologists. Unknown but probably numerous smaller or more deeply buried faults remain undetected. Even those faults that are mapped at the surface are poorly located at earthquake depths.
Accordingly, few, if any, earthquakes in the eastern Tennessee seismic zone can be linked to known faults, and it is difficult to determine if a specific fault could still slip and cause an earthquake. As in most other areas east of the Rockies, the best guide to earthquake hazards in the seismic zone is the earthquakes themselves.

Source:  U.S. Geological Survey