Multiple generations of earthquake-induced sand blows in Quaternary sediments and soils near Charleston, South Carolina, are evidence of recurrent moderate to large earthquakes in that area. The large 1886 earthquake, the only historic earthquake known to have produced sand blows at Charleston, probably caused the youngest observed blows. Older (late Quaternary) sand blows in the Charleston area indicate at least two prehistoric earthquakes with shaking severities comparable to the 1886 event.

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.

No abstract

No abstract