Earthquakes in SC
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Recent SC Earthquakes
The Palmetto state has a seismic past and will,
no doubt, tremble again as quakes shake the ground beneath our feet.
Earthquakes are not an uncommon occurrence in South Carolina. (See
the Report on the most recent 3.6 Magnitude Earthquake in the Lowcountry) The South Carolina Geological Survey
(SCGS) is interested in making South Carolinians aware of our seismic past,
what causes our earthquakes, what is being done to reduce the losses that
will result from future quakes, and what you should do before, during, and
after an earthquake.
Latest Earthquakes - Last 24 Hours (USGS)
Download South Carolina Earthquake Guide (Credit SCEMD) (12mb PDF,( requires Acrobat Reader))
Download Our Classroom Presentation on Earthquakes (1.7mb PDF, (requires Acrobat Reader))
Download South Carolina Earthquakes Brouchure (1.2mb PDF, (requires Acrobat Reader)) Credit SCEMD
Major Historical Earthquakes
Charleston earthquake of 1886
Most people had gone to bed by 9:51 p.m. on Tuesday,
August 31, 1886. They had no way of knowing that shock waves from a
massive quake (see Figure 1), estimated magnitude of 7.6, would throw them
out of bed. Imagine how bewildered and frightened they must have been as
they darted for safety when ceilings gave way and tons of debris rained down
about them. Survivors saw that many of Charleston's
brick and masonry buildings had crumbled to the ground. Those structures
that remained standing bore great cracks and other scars (see Figure 2).
Sadly, about 60 people did not survive the quake. It was reported that
ground shaking damaged structures as far away as 200 miles from Charleston.
This quake was the strongest earthquake known to hit the Eastern Seaboard,
and it shook with such force that it was felt over 2 1/2 million square miles
(from Cuba to New York, and Bermuda to the Mississippi River).
||Figure 1. Map showing earthquake epicenters of
the 1886 Charleston and 1913 Union County earthquakes.
||Figure 2. Damage caused by the historic Charleston earthquake of 1886.
Picture was taken on the south side of Broad Street.
See more photos of the Charleston Earthquake at the USGS
Union County earthquake of 1913
Twenty-seven years after the 1886 Charleston
earthquake and subsequent after shocks, 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 with an estimated
magnitude of 5.5 (Figure 1). Shock waves moved out from the western
portion of South Carolina into adjacent Georgia and North Carolina, and even
up into parts of Virginia. Fortunately, damage was minimal and
no deaths resulted. This event is significant because it demonstrates
that large, destructive earthquakes can strike the Piedmont region.
In South Carolina, geologists have recently discovered
evidence of at least five large paleoearthquakes during the past 5,000 years
(Amick and Gelinas, 1991). As shown in Figures 3 and 4, paleoliquefaction
features, considered earthquake induced, have been found in South Carolina's
coastal area. During a strong earthquake, subsurface saturated sand
becomes liquefied and this fluid mass can be ejected to the surface. The
resulting liquefaction features, sand blows, vents/fissures, landslide, and
differential compaction, are preserved in the soil as evidence of the
earthquake's occurrence and
strength. Given the necessary conditions, a magnitude 5.5 quake can
generate liquefaction features that could cause damage to existing
facilities and property.
Figure 3. Dry fissure along the bank of the Ashley River associated with
the 1886 Charleston earthquake.
||Figure 4. Sand blow crater associated with the 1886
What causes an earthquake?
An earthquake is the violent shaking of the Earth caused
by a sudden movement of rock beneath its surface. Rocks respond to stress
(squeezed or pulled apart) near the Earth's
surface by breaking, and when rocks move along either side of a fracture, it
is called a fault. The land around a fault may shift horizontally,
vertically, or a combination of these motions (see Figure 5). The force
that causes the stress within the rock is a result of movement of giant
sections of the Earth's crust (see
Figures 6 and 7).
Figure 5. The three basic types of faults are normal,
reverse, and strike-slip (lateral). (A) A normal fault is one in which the
rocks above the fault plane, the hanging wall, move down relative to the
rocks below the fault plane in the footwall. (B) A reverse fault is one
in which the hanging wall moves up relative to the footwall. (C) When rocks
on either side of a nearly vertical fault plane move horizontally, the
movement is called strike-slip.
Figure 6. Cross section of the Earth's crust
showing oceanic crust sliding under continental crust, and mountains being
built as a result of collision of two continents.
||Figure 7. The plates of the Earth's crust.
For hundreds of millions of years, the forces of
continental drift have reshaped the Earth. Continental drift is based on the
idea that the continents bumped into, and slid over and under each other and
at some later time broke apart. Today, most people accept the theory that
the Earth's crust is on the move,
and we call this theory plate tectonics. The crust (lithosphere) is broken
into about 12 enormous plates that float
on hotter, softer rocks in the underlying mantle (asthenosphere). The Earth's
heat drives convection currents in the asthenosphere, moving the
plates past one another very slowly. Plates move mere inches annually,
carrying the continents and ocean basins with them as they drift about.
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. Perhaps the
intraplate quakes felt in South Carolina are the result of stresses
transmitted inward from the boundaries of the North American plate. In our
state, quakes may occur along ancient plate boundaries where existing faults
are reactivated as the tectonic stress is released.
In response to this threat, SCGS has been mapping faults
and related geologic structures throughout the state. SCGS has published a
map, similar to the very generalized one shown in Figure 8, showing where
faults and other geologic structures in South Carolina are located. These
and other maps are being produced to increase the public awareness of
In South Carolina, approximately 70 percent of the
earthquakes occur in the Coastal Plain and most are clustered around three
areas west and north of Charleston: Ravenel-Adams Run-Hollywood, Middleton
Place-Summerville, and Bowman. These faults and other geologic
structures related to the earthquakes are hidden by the thick sequence of
sediments. Therefore, few clues to the causes of earthquakes in the Coastal
Plain can be found at the surface. To unmask these hidden geologic
structures, geologists are using geophysical techniques, recorded seismic
activity (see Figure 9), or both. In the Piedmont, studies of surface
geology are beginning to offer important clues to the causes of quakes in
||Figure 8. Simplified map showing mapped faults and related
geologic structures (shear zones) and inferred faults based on geophysical
Figure 9. Rails and roadbed owned by the Charleston &
Savannah R.R. have been deflected to the right. Photograph's view is north
70 degrees east. As one looks "up" the tracks, the deflected rails and
roadbed suggest a hidden fault (right-lateral).
Figure 10. A modified version of the Earthquake Hazards Map
for the Coastal Plain, showing geologic response to ground shaking.
Paleoliquefication sites are shown to quantify the interpretations of
Is there a major earthquake in South Carolina's
When will the next strong quake occur? The ability to
accurately predict when and where earthquakes will occur is not yet
available. South Carolinians need to realize that South Carolina faces the
possibility of the occurrence of a strong quake having its epicenter within
our borders. We also need to realize that a major earthquake
anywhere in the
Eastern United States could adversely affect us, causing damage.
SCGS is now conducting studies to evaluate the geologic
response to earthquake-induced motion in an attempt to help reduce the risk
to lives and property. An example of these studies is the map showing
where the Coastal Plain is most susceptible to severe ground shaking (Figure
10). Once data about an area have been gathered, maps that show levels of
risk for an area can be produced. Seismic-risk studies will become more
important as a statewide earthquake hazard mitigation strategy is developed.
What can you do to be prepared for the next Earthquake?
References for this information