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Thursday, May 24th a small 2.4 magnitude earthquake occurred approximately 12 miles SSE of Columbia SC. Though earthquakes of this magnitude and smaller occur relatively frequently (South Carolina has about 10 to 15 earthquakes with a magnitude 3 or less a year), this particular earthquake was notable in that it was felt by many in the Columbia area, descriptions ranged from a 'a car hitting the building' to 'a truck driving by'. Usually earthquakes between a magnitude 2 and 3 are felt only by those on the highest floors of buildings, (the movement of the ground is amplified by the height of the building). This is not Columbia's first earthquake, according to the USGS a small but powerful earthquake was centered in the vicinity of Lake Murray in July of 1945. That earthquake had an approximate intensity of IV-V on the Mercalli scale with the worst damage usually some windows and dishes being broken and reports of it being felt in parts of North Carolina, Georgia and Tennessee.
The earthquake on May 24th would probably fall on the Mercalli scale (a scale based on felt reports) as a III. It was also recorded by the University of South Carolina's (USC) seismic network and can be seen on the digitized Jenkinsville helicorder on the USC website (http://scsn.seis.sc.edu/). It is also probable based on the work done by the seismologist, Steve Jaume, at the College of Charleston that the earthquake was closer to Columbia than originally located, which would account for the large number of people who reported feeling it.
Columbia is situated on what is locally known as the Fall Line, so named for its waterfalls and rapid change in elevation. This change in elevation is due to a geologic boundary that marks the edge of one type of geologic province to the east (an area of sediment cover over stretched continental crust) and different geologic province (the Carolina slate belt) to the west. These two areas have undergone different geologic processes and have different rocks in them, and, most importantly for earthquakes, join together at a series of faults. These faults are active with smaller earthquakes from time to time as can be seen on the National Atlas image below with earthquakes of 3.5 and larger marked on the map. These small earthquakes do not necessarily mean that "the big one" is coming, more likely that the earth is making small changes all the time.
Curator: hallcr@cofc.edu
