The devastating earthquake that struck Charleston in 1886 remains, at 7.4 on the Richter scale, the strongest earthquake to ever occur on the East Coast, but it wasn't the last by any means. Smaller tremors have since been felt once or twice a decade, most recently in 2014, when a magnitude 4.1 rattled the Lowcountry. In fact, South Carolina is the most seismically active state east of the Rocky Mountains. Summerville, for example, was shaken by two quakes, in 1912 and 1914, felt not only in Charleston but as far south as Savannah and Macon, Georgia. Charleston itself experienced a series of minor tremors in 1959, 1960 (two of them that year) and 1967.
Geologists have long identified fault lines criss-crossing the midland and upstate regions of South Carolina. They're the buried but readily located remnants of ancient plate tectonics some 500-million years ago, when colliding prehistoric landmasses raised the Appalachians. The gathering pressures along such known faults that may result in earthquakes can usually be detected well in advance, but Charleston lies hundreds of miles from the nearest fault-prone plate boundary, under the Caribbean.
Here on the coast, geologists can only estimate where fault lines may lie within underlying bedrock, since the bedrock is buried under up to 3 miles of layers of sand, silt, clay and sedimentary rock, making it difficult for even modern technology to perceive early warnings of a pending tremor.
The 1886 quake began as a barely felt tremor before the main earthquake rocked the city. Aftershocks were felt for another 24 hours. Sixty people were killed amid estimated damages of $160 million in modern dollars. In rebuilding, the city mandated "quake bolts" for new construction and for retrofitting on the few structures that remained standing.
The good news is that most geologists think such major quakes occur only every five hundred years or so, allowing some breathing room before the Lowcountry once again is all shook up.