PALEOLIQUEFACTION STUDIES ALONG THE ATLANTIC SEABOARD - IMPLICATIONS FOR LONG-TERM SEISMIC HAZARD

The search for paleoliquefaction evidence of large prehistoric earthquakes is presently underway both within the epicentral area of the 1886 Charleston earthquake and elsewhere along the Atlantic seaboard. To date, no conclusive evidence of large prehistoric earthquakes originating outside of South Carolina has been found. However, in addition to liquefaction resulting from the 1886 earthquake, paleoliquefaction data indicate that perhaps as many as five prehistoric earthquakes greater than about M(b) 5.5 to 6.2 occurred near Charleston during Holocene times. Furthermore, the data suggest that past large earthquakes within coastal S.C. may have not been limited exclusively to the established Charleston epicentral area. The mean return period for large liquefaction associated earthquakes is about 600 years for the past four earthquake cycles. Since only about 100 years have elapsed since the 1886 event, the probability of a similar earthquake occurring within the next several decades is judged to be low. However, the hazard presented by smaller earthquakes should not be overlooked.