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VIRGINIA POLYTECHNIC INSTITUTE AND STATE UNIVERSITY, BLACKSBURG, VIRGINIA 24061
Abstract
The seismic history of South Carolina is dominated by the great Charleston earthquake of August 31, 1886. In addition to having several unusual aspects (region essentially free from shocks for preceding 200 years, large felt area, dual epicenter points, "low intensity zone" in West Virginia), that intensity X event seriously perturbed the seismic regime of the area for at least the following 30 years. Of 438 earthquakes reported to have occurred in the state between 1754 and 1971, 402 have been in the Charleston-Summerville area. The remaining 36 shocks form a southeasterly-trending zone of activity that is transverse to the structural grain of the Appalachians.
For the 60 shocks assigned an intensity value (1886-1971), a recurrence relationship between the number of earthquakes "N" of maximum intensity "I0" was found to be log N = 0.52-0.31 I0 for IV 
I0 VIII. This corresponds to a "b" value of 0.5 ± 0.1 in log N versus M relationship assuming M = 1 + (2/3)I0. These data suggest a frequency of seismic activity comparable to that reported for the New Madrid seismic zone.
Three months of microearthquake monitoring in the Charleston area during the summer of 1971 yielded 505 hr of low-noise data. Sixty-one earthquakes, primarily in swarm occurrence, were recorded. An h value of 1.8 ± 0.5 was determined for these microshock events. This value is similar to that previously observed for a swarm sequence in New Jersey.
Four shocks occurred in the state during 1971. Three of these events (May 19, July 31, August 11) were in the central part of the state near Orangeburg, while the third event (July 13) was near Seneca in northwestern South Carolina. All three events had 3.0 < ML < 4.0. Similar episodes of three or four shocks in 1 year happened in 1956 and again in 1965. The Orangeburg area had, according to historical data, been previously free of earthquake epicenters.
This article has been cited by other articles:
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  P. Talwani, P. TALWANI, and J. COX Paleoseismic Evidence for Recurrence of Earthquakes near Charleston, South Carolina Science, July 26, 1985; 229(4711): 379 - 381. [Abstract] [PDF]
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 A. C. TARR, P. TALWANI, S. RHEA, D. CARVER, and D. AMICK Results of recent South Carolina seismological studies Bulletin of the Seismological Society of America, December 1, 1981; 71(6): 1883 - 1902. [Abstract] [PDF]
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P. TALWANI, D. STEVENSON, D. AMICK, and J. CHIANG An earthquake swarm at Lake Keowee, South Carolina Bulletin of the Seismological Society of America, June 1, 1979; 69(3): 825 - 841. [Abstract] [PDF]
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J. G. ANDERSON On the attenuation of Modified Mercalli Intensity with distance in the United States Bulletin of the Seismological Society of America, August 1, 1978; 68(4): 1147 - 1179. [Abstract] [PDF]
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P. TALWANI An intensity survey of the April 28, 1975 Summerville, South Carolina earthquake Bulletin of the Seismological Society of America, April 1, 1977; 67(2): 547 - 549. [PDF]
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L. T. LONG Earthquake sequences and b values in the southeast United States Bulletin of the Seismological Society of America, February 1, 1974; 64(1): 267 - 273. [Abstract] [PDF]
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