\nThe Eastern Tennessee seismic zone extends across Tennessee and northwestern Georgia \ninto northeastern Alabama. It is one of the most active earthquake areas in the Southeast. \nAlthough the zone is not known to have had a large earthquake, a few earthquakes in the \nzone have caused slight damage. The largest known (magnitude 4.6) occurred on April \n29, 2003, near Fort Payne, Alabama. Earthquakes too small to cause damage are felt \nabout once a year. Earthquakes too small to be felt are abundant in the seismic zone, and \nseismographs have recorded hundreds of them in recent decades.\n
\n\nEarthquakes in the central and eastern U.S., although less frequent than in the western \nU.S., are typically felt over a much broader region. East of the Rockies, an earthquake \ncan be felt over an area as much as ten times larger than a similar magnitude earthquake \non the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many \nplaces as far as 100 km (60 mi) from where it occurred, and it infrequently causes \ndamage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as \nfar as 500 km (300 mi) from where it occurred, and sometimes causes damage as far \naway as 40 km (25 mi).\n
\n\n\nEarthquakes everywhere occur on faults within bedrock, usually miles deep. Most of \neastern Tennessee's bedrock originated several hundred million years ago, as the \nAppalachian Mountains were formed.\n
\n\nAt well-studied plate boundaries like the San Andreas fault system in California, often \nscientists can determine the name of the specific fault that is responsible for an \nearthquake. In contrast, east of the Rocky Mountains this is rarely the case. The Eastern \nTennessee seismic zone is far from the nearest plate boundaries, which are in the center \nof the Atlantic Ocean and in the Caribbean Sea. The Eastern Tennessee seismic zone is \nlaced with known faults but numerous smaller or deeply buried faults remain undetected. \nEven the known faults are poorly located at earthquake depths. Accordingly, few, if any, \nearthquakes in the Eastern Tennessee seismic zone can be linked to named faults. It is \ndifficult to determine if a known fault is still active and could slip and cause an \nearthquake. As in most other areas east of the Rockies, the best guide to earthquake \nhazards in the seismic zone is the earthquakes themselves.\n
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