FIRST ALERT: South Carolina’s fault lines and earthquake history
MYRTLE BEACH, SC (WMBF) - A recent rash of earthquakes in central South Carolina proves that while large earthquakes are highly uncommon, the Palmetto State does have a geologically active past and is vulnerable to future quakes.
Since late December of 2021, a total of 10 earthquakes have rattled Kershaw County, SC with most of the activity centered near Elgin and Camden. The first quake, a magnitude 3.3, was the largest and felt as far away as Columbia. The following 9 earthquakes have most likely been aftershocks and weaker than the first shake.
According to the South Carolina Emergency Management Division, approximately 10 to 20 earthquakes are recorded each year in South Carolina with only 3 to 5 of them felt or noticed by people.
Unlike more traditionally earthquake prone regions like the West Coast of the U.S, the reason behind earthquakes in South Carolina is a little more unlcear. According to the Department of Natural Resources, “The majority of earthquakes worldwide occur at plate boundaries when plates stick and then jump past each other. These quakes often are the ones that are the most destructive and well understood in terms of plate tectonics. The cause of earthquakes in South Carolina is not so clear. South Carolina’s quakes are located within a plate rather than at a plate boundary. In our state, quakes may occur along ancient plate boundaries where existing faults are reactivated as geological stress is released. Studying these faults is difficult since many of the most previously active faults are buried deep in sediment across the coastal plain.
In South Carolina, approximately 70 percent of the earthquakes occur in the coastal plain and most are clustered around areas west and north of Charleston. This area has the highest concentration of ancient fault lines in the state.
The top 15 most seismically active and vulnerable states in the US are Alaska, Hawaii, California, Oregon, Washington, Nevada, Utah, Idaho, Montana, Wyoming, Missouri, Arkansas, Tennessee, Illinois, and Kentucky. South Carolina comes in at number 16 and has the highest risk of any east coast state. One of the primary reasons South Carolina is vulnerable to damage from earthquakes is through a process called liquefaction - a process in which a saturated sand softens and loses strength due during strong earthquake ground shaking. This can cause severe damage to structures as the ground beneath them becomes highly unstable.
The strongest earthquake on record to hit the eastern U.S. struck near Charleston on the night of August 31st, 1886. The violent tremors went on for a full minute and the quake measured a magnitude 7.6. This quake was the strongest earthquake ever known to hit the Eastern Seaboard, and it shook so violently that it was felt from Cuba to Bermuda to Chicago and Boston. Structural damage was widespread, extending as far as Alabama, Ohio, and West Virginia. Almost all of the buildings in town were seriously damaged. It is estimated that 14,000 chimneys fell in Charleston from the shaking. It caused multiple fires and water lines and wells were ruptured and broken. Railroad tracks were bent in all directions in some locations across the Low Country. Aftershocks continued to rattle the region for months.
Twenty-seven years after the 1886 Charleston earthquake, another strong earthquake occurred in South Carolina. This quake was on the afternoon of January 1, 1913, at 1:28 p.m. near the town of Union in Union County. This quake struck with a magnitude of 5.5. Shaking was felt from the western portion of South Carolina into northern Georgia and North Carolina, and even up into parts of Virginia. Damage was minimal and no deaths resulted.
IS ANOTHER LARGE QUAKE POSSIBLE?
The fact that South Carolina has already seen a large quake in the past means that another large event is likely although when and where is virtually impossible to predict.
In 2001, the South Carolina Emergency Management Division conducted an in depth study on the risk and potential damage from earthquakes in the future. The study modeled a 7.3 earthquake near Charleston similar to the 1886 quake. According to the study, a quake of that magnitude today would result in economic losses due to building damage to be over $14 billion across the state. Widespread power failure, transportation disruption and water system issues would follow.
The study went on the model weaker quakes and the potential impacts.
The study stated that “in the event of a magnitude 6.3 earthquake in Charleston, approximately 136,000 buildings will sustain slight to moderate damage and 25,000 will be extensively damaged. Total building loss including capital stock and income losses will exceed $2 billion.”
When modeling a magnitude 5.3 Charleston earthquake scenario, the report went on to state that “the losses and casualties decrease significantly. Injuries will number less than 100 with no estimated deaths. Total loss to buildings will be about $230 million.”
The study also examined the potential impact of a smaller earthquake near Columbia. If a magnitude 5.0 were to occur in Columbia, “approximately 400 buildings would sustain slight or moderate damage with a total loss of $310 million.”
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