The spacial distribution of seismically induced liquefaction features discovered along the Atlantic seaboard suggest that during the last 2000 to 5000 years, large earthquakes (body wave magnitude, m(b) >/= 5.8 +/- 0.4) in this region may have been restricted exclusively to South Carolina. Paleoliquefaction evidence for six large prehistoric earthquakes was discovered there. At least five of these past events originated in the Charleston, South Carolina, area, the locale of a magnitude 7+ event in 1886. During the past two millennia, large events may have occurred about every 500 to 600 years.

The ages of seismically induced paleoliquefaction features located in the Charleston, S. C. area suggest that the return period between large events similar to the 1886 earthquake is much longer than the historic record. If large prehistoric earthquakes have occurred elsewhere along the Atlantic Seaboard, then evidence of liquefaction features associated with them should be present in unconsolidated Pleistocene and Holocene deposits. To establish a comprehensive control data base for a regional analysis, liquefaction sites and features located in the Charleston area have been evaluated. Over 100 liquefaction sites were identified on the basis of a detailed review of historical accounts of the 1886 earthquake, and results of recent field studies. These studies then centered on characterizing the geologic, stratigraphic, and hydrologic setting of these sites and identifying criteria by which similar locales could be recognized elsewhere in the Atlantic Coastal Plain. This investigation also included the development of recognition criteria to distinguish seismically induced liquefaction features from pseudoliquefaction features (other features which look similar but are not seismic in origin). Guided by these findings, a systematic search for paleoliquefaction features outside the epicentral area of the 1886 Charleston earthquake is now underway.

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An earthquake swarm occurred near Lake Keowee, South Carolina in January to February 1978. The swarm was monitored by using portable seismographs. The shallow (<3 km), low level (ML ≦ 2.2), intense (up to 200 events per day) activity occurred in a narrow elliptical epicentral region (2 by 3 km). This active area trends NW-SE, normal to local geologic grain, and appears to be related to the steeply dipping NE trending joints. A search for earlier seismicity in the area suggests that this swarm is possibly related to the Seneca earthquake of 1971 which followed the impounding of Lake Keowee.

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