Not many people are aware of it, even in that region, but both the eastern and western ends of Tennessee have major fault lines, that are both active. Further, when earthquakes hit on those faults, they tend to have far more widespread (geographically) effects than in California. One that is a "5" on the Richter scale in this area will do far more damage than a "5" in California, both because it will travel farther (see the map for a comparison of two earthquakes of similar magnitude), and because the people and structures in those areas are far less prepared for earthquakes.
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One of the worst earthquakes this country has ever seen occurred in the early 19th century in that area, epicentered near New Madrid, Missouri. If that same earthquake were to hit today, both Memphis and St. Louis would be long-term federal disaster areas, likely with thousands of deaths.