\nCharleston and its surroundings were devastated in 1886 by a very large earthquake \n(magnitude 7.3). Aftershocks, some of them large enough to be damaging by themselves, \ncontinued for years. Prehistoric earthquakes of similar size to the 1886 shock have \noccurred in coastal South Carolina at intervals of several centuries to several thousands of \nyears. In recent decades, smaller earthquakes that cause little or no damage have been felt \nroughly once a year in coastal South Carolina and a small part of adjacent Georgia.\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 \nbedrock beneath the Charleston area was assembled as continents collided to form a \nsupercontinent about 500-300 million years ago, raising the Appalachian Mountains. \nMost of the rest of the bedrock formed when the supercontinent rifted apart about 200 \nmillion years ago to form what are now the southeastern U.S., the Atlantic Ocean, and \nAfrica.\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 \nCharleston area is far from the nearest plate boundaries, which are in the center of the \nAtlantic Ocean and in the Caribbean Sea. Bedrock and its faults are buried beneath sand, \nsilt, clay, and sedimentary rocks that may be as thick as 1-3 km (1-2 mi). Accordingly, \nfew earthquakes in the Charleston area can be linked to named faults. It is difficult to \ndetermine if most known faults are still active and could slip and cause an earthquake. As \nin most other areas east of the Rockies, the best guide to earthquake hazards in the \nCharleston area is the earthquakes themselves.\n
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