Earthquakes

Earthquakes (seismic events) have impacted South Carolina for thousands of years. The state’s earthquakes have been tectonic; that is, they have resulted from intraplate displacements on the North American plate and not from interplate movements. They generally have caused little serious damage. Exceptions have been the massive Charleston earthquake of 1886 and the Union County earthquake of 1913. Earthquakes in South Carolina historically have been unpredictable and quite varied in their nature.

According to seismologists, South Carolina is one of the most seismically active states east of the Mississippi River, with most activity taking place in the Charleston-Summerville area. All except five or six of the state’s northeastern counties have been the source of earthquakes at one time or another. Between February 1698, when South Carolinians first reported feeling an earthquake, and 2002 South Carolina witnessed about 180 earthquakes that have measured a magnitude 3 or greater on a 10-point scale (or a V on a modified Mercalli Intensity Scale of I to XII). Most seismologists consider such events to be major earthquakes.

Since the late 1600s, South Carolina has had twelve earthquakes with magnitudes of 4.0 to 4.9 and three with magnitudes of 5.0–5.9 (these three, however, were aftershocks to the great 1886 earthquake). Eight originated near Charleston and Summerville. The other seven originated in Union County, Pickens County, Columbia/Lake Murray, McBee, Bowman, Orangeburg, and Lake Jocassee.

Earthquake activity in South Carolina did not capture much attention until the giant Charleston earthquake of August 31, 1886. With a moment magnitude of 7.3 and an intensity of X, the 1886 earthquake remains the largest and most powerful seismic event to occur in the southeastern United States. It was also one of the first major U.S. earthquakes to be systematically and scientifically documented by the U.S. Geological Survey (USGS). The epicenter was south of Summerville at Middleton Plantation along the Ashley River. Its cause was movement at the junction of two intraplate faults–the north-northeast trending Woodstock fault and the northwest trending Ashley River fault. The earthquake hit at 9:51 p.m. Charleston time, and it shook the port city for thirty-five to seventy seconds (an unusually long time for an earthquake). It was followed by almost daily aftershocks for several weeks. Strong aftershocks shook the Charleston-Summerville area on September 2, 3, and 5, and even stronger ones impacted the area on October 22 and November 5. Many seismologists contend that aftershocks to the great earthquake continued at least into 1893. Upward of fifty-three of these aftershocks had magnitudes of 3.3 or more.

The Charleston earthquake was felt across two million square miles, including all of South Carolina, most of the United States east of the Mississippi River, and as far away as Canada, Cuba, and Bermuda. Of the eastern U.S. earthquakes, it was second only to the mammoth New Madrid, Missouri, earthquakes of 1811 and 1812 in the area that it impacted. The earthquake caused extensive damage to buildings not only in Charleston and Summerville, but also in Augusta and Savannah, Georgia. It destroyed two millpond dams in Aiken County and created a three-foot-high wave that inundated rice fields along the Cooper River and affected ships in Charleston’s harbor and at sea. It reportedly chased rats out of sewers in New York City, rocked lighthouses along the New York seacoast, and felled chimneys in Kentucky and Ohio. The death toll eventually reached eighty-three in Charleston alone, with additional deaths attributed to the earthquake occurring elsewhere in South Carolina and in other states. The earthquake caused more than $5 million worth of damage in Charleston, whose estimated total assets in buildings in 1886 was about $22.5 million. It was South Carolina’s worst natural disaster until Hurricane Hugo in 1989.

The Charleston-Summerville area continues to be by far the most seismically active area in the state. But, as South Carolina’s seismic history shows, other areas also can have earthquakes. In the 1980s governments and organizations increasingly worried about threats from future earthquakes. In 1981 concerned South Carolinians formed the S.C. Seismic Safety Consortium (SCSSC) to work with the newly created Southeastern United States Safety Consortium (SEUSSC) in developing comprehensive action plans for earthquake preparedness. However, even with planning, a major earthquake would create major problems for the state’s population and infrastructure. In the twentieth century, some rivers and streams in South Carolina were dammed to create hydroelectric, flood control, and recreational facilities or, in the cases of the Monticello Reservoir and Lake Keowee, sources of water cooling for atomic energy plants. Many of the dams were built on or near fault zones. To date, earthquakes have not broken or weakened the dams. In 2001, however, officials with the federal government, noting significant earthquakes in the Columbia region in 1945 and 1964, decided to make a concerted effort to protect area inhabitants against a major earthquake. Concerned about the capacity of the Lake Murray dam to withstand such an earthquake, they mandated the construction of a back-up dam to the existing earthen dam that was constructed in the late 1920s. An earthquake of magnitude 3.3 (intensity IV) in 1975 at Lake Jocassee also has caused speculation about that lake’s dam. Dutton, Clarence E. The Charleston Earthquake of August 31, 1886. Arlington, Va.: Department of the Interior, Geological Survey, 1979.

Gohn, Gregory S., ed. Studies Related to the Charleston, South Carolina, Earthquake of 1886: Tectonics and Seismicity. Geological Survey Professional Paper 1313. Washington, D.C.: Government Printing Office, 1983.

Peters, Kenneth E. “Economic Consequences of the Charleston Earthquake.” Proceedings of the South Carolina Historical Association (1986): 70–81. Peters, Kenneth E., and Robert B. Herrmann, comps. and eds. First-Hand

Observations of the Charleston Earthquake of August 31, 1886, and Other Earthquake Materials. Columbia: South Carolina Geological Survey, 1986.

Talwani, Pradeep. South Carolina Earthquakes, 1698–1995. Columbia: South Carolina Seismic Network, 1996.

Visvanathan, T. R. Earthquakes in South Carolina. Columbia: South Carolina Geological Survey, 1980.