An earthquake occurs when there is a rapid release of energy in the Earth's crust, causing violent shaking of the Earth's surface. It is one of the most destructive natural disasters that result in significant deaths and property destruction globally. While most earthquakes are small, the big ones (with a lot of force and intensity) happen on average only once every 5 to 10 years. In the US, the risk of earthquakes is highest on the west coast, the island of Hawaii, Alaska's southern shore, and the western mountain range. The most severe earthquakes occur in these places rather than in the eastern or central United States, which includes South Carolina.
South Carolina is the most earthquake-prone state in the eastern United States. However, most of the earthquakes in its history have been of minor scale and intensity. Still, state residents must build efficient disaster management plans and better understand earthquakes to protect important infrastructure like roads, housing, and businesses.
An earthquake happens when huge masses of rock beneath the Earth's surface move. Tectonic plates are rock masses that make up the crust (the Earth's outermost layer). These plates are in constant motion, colliding or sliding over each other. The movement causes a significant amount of pressure between the plates over time. When there is too much pressure, the rock masses shift and cause a fault.
The result of a fault are shocks or seismic waves produced as the shifting plates release their stored energy. The waves radiate outward in all directions from the point where energy is released. These waves travel through or over the Earth, and an earthquake occurs. Although the movement of tectonic plates often causes earthquakes, a few other factors can cause them. Examples include volcanic eruptions, underground collapses, and man-made explosions. Volcanic-tectonic earthquakes are generated by faults sliding near a volcano. Collapse earthquakes are small underground quakes that occur in caves or mines, and explosion earthquakes are caused by the detonation of nuclear or chemical explosives.
The focus or hypocenter is the point where an earthquake begins beneath the Earth's crust. The epicenter is the point on the Earth's surface directly above the focus. The maximum intensity of an earthquake is felt near the epicenter. However, earthquake vibrations can be felt and identified hundreds or even thousands of miles away from the earthquake's epicenter. Also, aftershocks nearly always occur in the aftermath of big quakes. These smaller earthquakes happen in the same location as the main earthquake. Depending on the initial earthquake's severity, aftershocks can last for weeks, months, or even years.
Due to their unpredictability and extensive destructive capabilities, earthquakes are monitored and documented. Scientists use seismographs to record earthquake data. The equipment detects and records seismic waves. The data helps scientists to determine the date and location of an earthquake, as well as its magnitude. The magnitude of an earthquake is a measure of the size of its source. Magnitude is represented with whole numbers or decimals. Earthquakes of magnitude 2.5 or less are usually not felt, but they are detected solely by seismographs, but any quake with a magnitude of 5.5 or more would cause slight to extensive damage.
A major earthquake can alter the Earth's surface and expose massive faults in the ground. When an earthquake occurs, buildings, bridges, railways, and other structures are vulnerable to catastrophic damage. Because of increasing urbanization and a growing population, the overall effects are expected to worsen in the coming years.
Most of the earthquake damage is caused by the accompanying events, including:
Ground Shaking. Earthquakes disseminate seismic energy as both body waves and surface waves. Body waves, which flow into the Earth's interior, vary from surface waves, which can only move over the planet's surface like ripples in water. Ground shaking can be ascribed to the interaction of surface and body waves. Buildings may experience damage as a direct result of the shaking or the ground beneath them sinking to a different level than before the earthquake (ground displacement). The severe shaking that happens during earthquakes can also cause different ground movements, triggering other disasters such as avalanches, landslides, and tsunamis.
Surface Faulting. Surface faulting or rupturing occurs when earthquakes push or pull apart the Earth's surface. It involves differential movements caused by deep-seated earth forces, the progressive migration of sedimentary deposits toward the Gulf of Mexico, and faulting associated with salt domes. The phenomenon occurs when there is movement in either the vertical or horizontal planes on either side of a ruptured fault. It could happen gradually or suddenly during an earthquake. The shifting of the Earth, which may affect large areas of land, can cause substantial damage to buildings, streets, railroads, and pipelines, especially in places with a lot of land utilization.
Ground Failure Caused by Liquefaction. During earthquakes, a physical process known as liquefaction can eventually lead to ground failure or collapse. It occurs when the Earth's shaking destabilizes the sand or soil layers and turns them into liquid. Liquefaction may weaken the foundations and supports of structures such as buildings, bridges, pipelines, and roadways, causing them to sink into the soil or collapse.
Furthermore, liquefaction at shallow depths can occasionally result in sand boils, causing water and sediment or sand to bubble to the ground's surface. Sand boils are a harmful natural phenomenon that can cause local flooding and silt deposition or accumulation.
Tsunamis. Tsunamis are giant waves in the ocean caused by undersea earthquakes or volcanic eruptions. They endanger people's lives, property, and the infrastructure supporting them. Tsunamis can cause destruction in the immediate vicinity and in locations several miles away from where they form.
Flooding. Flooding is a secondary impact of earthquakes. Large earthquakes can generate tsunamis that can inundate coastal areas. Furthermore, an earthquake has the potential to breach or destroy dams or levees, resulting in the reservoir's water flooding the area, causing damage to buildings, and possibly sweeping people away or drowning them.
Fires. Fires are a common hazard during earthquakes. Earthquake-caused fires start when electrical and gas lines become entangled due to the ground shaking. When gas lines burst, gas escapes, increasing the likelihood of a firestorm igniting.
Earthquake-induced Landslides. The severe shaking of the Earth caused by an earthquake can cause landslides in areas prone to them. Landslides can occur when an earthquake makes a slope unstable, either because of the inertial stress it imposes or because it causes a loss of strength in the elements that constitute the slope.
Lost Economic Growth. Although earthquakes have severe immediate consequences, they can also have long-term effects on economic growth. A major earthquake will result in substantial financial losses due to extensive structural damage, disruption of business activities, and population displacement. These would impact governments at all levels, especially state and municipal governments because they would lower future revenue, raise current expenses due to response operations, and increase future expenditures due to recovery and rebuilding operations.
South Carolina is the most seismically active state on the east coast. Seismic activity is the frequency and magnitude of earthquakes in an area. Earthquakes in the state can cause extensive damage in minutes and result in sudden and considerable loss. Although South Carolina has not had any big earthquakes in recent years, a 2001 study (the Comprehensive Seismic Risk and Vulnerability Study for the State of South Carolina) discovered that the state is highly vulnerable to seismic activity. The study also provides information regarding the potential impacts of earthquakes on the existing population and modern structures and systems.
The Coastal Plain is home to most of the state's earthquakes. The three most earthquake-prone areas in South Carolina are Ravenel-Adams Run-Hollywood, Middleton Place-Summerville, and Bowman, which are located to the west and north of Charleston. The underlying rocks in the Coastal Plain are heavily faulted or broken due to tectonic plate separation. These cracks in the deep rocks indicate that the plate in this area is weak. If pressure is applied to the plate's edge, the rocks can move eventually leading to earthquakes.
Unlike other earthquake-prone areas, such as the western coast of the United States, the cause of earthquakes in South Carolina is not well known. Most earthquakes globally occur near plate boundaries when plates move against each other. However, the epicenters of South Carolina earthquakes are located within plates rather than at plate boundaries. Studying the unusual behavior of these faults is complicated because many of the once active faults are now buried behind layers of silt scattered throughout the Coastal Plain. The thick sequence of sediments obscures these faults and other geologic characteristics associated with earthquakes.
Earthquakes pose an even more significant threat because scientists cannot predict when and where they will occur. Residents of South Carolina must note that the state is at risk of being hit by a major earthquake with the epicenter within its borders. Also, a major earthquake in any area of the Eastern United States might severely influence South Carolina and cause significant destruction.
The South Carolina Geological Survey (SCGS) is attempting to reduce the risk of earthquake-induced motion to people's lives and property by mapping faults and other related geologic formations throughout the state. The map depicts the Coastal Plain areas most likely to suffer strong ground shaking and locations of South Carolina's faults and other geologic structures. These maps are a bigger effort to improve public awareness about earthquake-prone areas.
Here is a round-up of notable earthquakes that have hit South Carolina in the past 14 decades:
An earthquake struck the midlands of South Carolina on February 14, 2014, at 10:23 p.m. The earthquake's epicenter occurred near Edgefield, South Carolina, and it was felt throughout South Carolina, Georgia, and western North Carolina. The quake was reported to have reached 4.1 on the Richter scale, which is rare for South Carolina.
According to geologists, the earthquake may have been triggered by the subsurface breakup of the old Appalachian Mountains. The rupture of a fault is not the only cause of earthquakes. Earthquakes may also occur near dams owing to water pressure and near the Appalachian Mountains. They believe that continuing sedimentation along a minor fault line has loosened a subsurface mega-boulder sufficiently for it to thrust upward with enough power to roil the soil abruptly, causing an earthquake.
On Monday, November 11, 2002, an earthquake of magnitude 4.2 struck areas near Seabrook Island, South Carolina. The earthquake did minimal damage, and there were no casualties.
Another major quake shook the state on the afternoon of January 1, 1913, near the town of Union in Union County, the quake's magnitude was estimated to be 5.5. Shock waves swept from the western part of South Carolina into neighboring states, Georgia and North Carolina, and some even found their way into northern Virginia. However, no one was killed, and minimal damage was done.
The earthquake that struck the Summerville and Charleston area on August 31, 1886, was the most devastating natural disaster to hit the southeastern United States. This earthquake was the most catastrophic in the United States during the nineteenth century, based on the number of lives lost and the extent of the devastation. It resulted in 60 fatalities, and buildings were reported to be destroyed up to 200 miles from Charleston. The 7.3 magnitude earthquake was felt in a 2.5 million square mile region stretching from Cuba to New York and Bermuda to the Mississippi River.
Geologists have recently discovered evidence of at least five large paleoearthquakes (earthquakes recorded geologically) in South Carolina during the past 5,000 years. Current study findings suggest that the coastal region of South Carolina contains traces of paleoliquefaction, which is assumed to be triggered by earthquakes.
Paleoliquefaction describes any liquefaction features that may be attributed to seismic events that occurred before measurements or written records of earthquakes were developed. Signs of liquefaction, such as sand blows, have been maintained in the soil as proof of the earthquake's occurrence and amplitude. If the conditions are favorable, a magnitude 5.5 earthquake has the potential to develop liquefaction characteristics, which might cause damage to both existing infrastructure and property.
It is worth noting that regions, where earthquakes have occurred, are likely to experience them again. In that case, it is plausible to expect these areas to be hit by another event of the same magnitude in the years ahead.
A swarm is a series of earthquakes that are mostly shallow and lack a distinct mainshock. Swarms typically exist for a short time, although they can sometimes linger for days, weeks, or even months. They usually occur in the same locations time and over.
A series of earthquakes recently hit the state of South Carolina. According to the Department of Natural Resources, at least 62 earthquakes have been observed in the state as part of an "earthquake swarm" since the beginning of 2022. With the exception of five earthquakes, the Midlands has been the epicenter of all of them.
Scientists have not found a credible explanation for the most recent events. Some experts attribute the frequency of the quakes to the faults in the Earth's surface and high water levels of the Wateree River that caused water to seep deep into the ground. Other likely possibilities that have been investigated include mining activity such as digging, water seeping through the soil from lakes, and different variations in the weight or pressure beneath.
Earthquakes can strike with little or no warning. So, the best preparation is before it happens. If a household or family is prepared, they afford themselves a significant opportunity of making the most of a difficult situation. South Carolina residents must prepare for an earthquake by:
This plan informs every household member on how to respond to an earthquake. The plan must include:
Putting together a readily accessible emergency kit
Learning first aid procedures
Compiling a list of emergency contacts, including the local police department, fire department, and emergency medical services.
Specifying escape routes from the home to meeting locations
A list of phone numbers and locations of close family members and friends
Periodic practice drills
Considerations for pets.
A good emergency kit should include provisions that may be used for up to three days. The kit should contain:
A first-aid kit and manual
A flashlight and replacement batteries
A battery-powered radio and replacement batteries
Foods in cans or other non-perishable containers
A can opener
Copies of important personal documents
In addition to the materials required for basic survival, an emergency kit should include extra items that may cater to the individual needs of its owner in the case of various disasters. These might include prescription medication, medical insurance and Medicare card copies, physicians' names, and contact information. Residents should also download the South Carolina Emergency Management Division app to build and monitor emergency plans and supplies.
Preparing financially for an earthquake is essential to avoid expensive recovery costs. One of the first steps in preparing to be resilient in an earthquake is obtaining earthquake insurance. Earthquake insurance covers damages and losses associated with earthquakes.
A homeowner's insurance policy will likely not pay to repair or replace any earthquake-related damage to a home or property. This means that if a household does not have an earthquake endorsement on their homeowner's insurance policy or a separate earthquake policy, they will be liable for the expense of repairing or rebuilding their property if it is destroyed in an earthquake.
In most situations, earthquake insurance only covers actual property damage caused by shaking induced by an earthquake. Some indirect damage, such as fire and water damage caused by ruptured gas and water lines, are covered by a homeowner's insurance policy. The whole state of South Carolina is at a moderate to high risk for earthquakes. All residents should consider insurance to protect their finances and property. As part of the preparation for unforeseen catastrophes, a family may consider starting a Catastrophe Savings Account (CSA) that allows them to save money on taxes while also protecting themselves financially in the case of a disaster.
The shaking induced by a strong earthquake can cause structural damage to buildings and also relocate nearly everything within the structure. Heavy furniture and other objects that fall on people during earthquakes are the most common source of harm during these natural catastrophes. As a result, preparations reinforcing the property:
Property owners should consider upgrading their structures to solve any structural flaws that might cause their buildings to collapse in the case of an earthquake
Fix any large items of furniture to the walls.
Put objects that are likely to break, including glass jars and china, in low-secured cabinets with locks.
Securely fasten overhead lighting fixtures to the ceiling.
Know where to shut off utilities
Use bolts or straps to secure large items that may topple over, such as a bookcase, china cabinet, or water heater.
Avoid putting anything heavy on shelves
For insurance purposes, create an inventory of all valuables to aid any insurance claims
Before laying the foundation of any construction in earthquake-prone areas, contact architects and structural experts.
Since scientists are unable to predict earthquakes, existing earthquake warning and alert systems can only warn people of existing earthquakes or when tremors may occur. The alert systems detect ground motion as soon as an earthquake begins and quickly send out alerts that an earthquake is on its way, giving people time to prepare.
The United States Geological Survey (USGS) is an organization investigating the geology of the United States, its natural resources, and natural hazards such as earthquakes. Its significant concentration is in the country's western area. This organization will alert residents of any earthquakes that occur in real-time. When earthquakes happen in a user's location, the Earthquake Notification Service (ENS) sends notifications to the user's mobile phone or email address. This service is entirely free.
Besides waiting for earthquake alerts from the authorities, there are other ways to know if an earthquake is coming. However, these signs are not always accurate.
Abnormal animal behaviors: There have been reports of animals such as toads, bees, birds, and bears abandoning their homes or breeding grounds right before an earthquake. It is unknown why animals can sense approaching events, but abnormal pet or animal behaviors might signal an earthquake.
Water level fluctuations in wells: Massive earthquakes can cause water-level changes in wells depending on the local geological properties of the well. Earthquakes stress the Earth's crust, and its aquifer systems, causing groundwater levels to vary abruptly in the near field of an earthquake
Foreshocks: These are earthquakes of small magnitude that sometimes precede larger earthquakes. Individuals who notice one or more small earthquakes must note that a bigger one may be heading in that direction. Individuals who feel or witness earthquakes in South Carolina must report them immediately.
An awareness of the seismic risks in an area allows residents to take precautionary steps and reduce their chances of suffering injuries, property damage, or financial hardship in the case of an earthquake. Seismic risk is the likelihood that an earthquake will cause damage to a structure, system, or other entity. It also constitutes the disaster's potential negative impacts on the economy, society, and environment within a short period.
USGS defines seismic risk by these elements:
The magnitude of the seismic hazard. The United States has a broad spectrum of seismic risk levels, with each state having its distinct profile. The USGS Earthquake Hazard Maps display the varying levels of risk throughout South Carolina.
Exposure to the hazard. Exposure and casualties in an earthquake are based on the number of persons in the high-risk zones, and the number and quality of infrastructure in the area
The vulnerability of the population and property to the hazard. One of the key elements determining a building's vulnerability to seismic damage is the existence or lack of earthquake-resistant construction and sound seismic engineering principles. Buildings that adhere to current building codes and satisfy all necessary criteria are less likely to sustain damage, even if they are located in a region with a high seismic hazard.
Safety is the priority during an earthquake. Hence, residents are advised to drop, cover, and hold on during an earthquake when the shaking starts.
Drop: Residents must immediately drop to the floor on their hands and knees. This stance allows them to be safe from falling but still be able to move if necessary.
Cover: Residents should take cover or shelter under a sturdy piece of furniture.
Hold on: Residents should hold on to their shelter until the shaking stops. If the shaking forces the shelter to move, the individual is advised to move with it.
Other ways to stay safe during an earthquake include:
Find an emergency kit if one does not already have one on their person
Stay away from windows, exterior doors, and other items that might fall
Remain sheltered until the shaking stops and local authorities establish that it is safe to go outdoors again.
If one is outside, the best place to seek refuge is in an open area away from buildings, trees, or power lines.
Inside a public building, avoid the stairwells and elevators and instead head for the exits.
Evacuate the area if the local authorities advise it.
Maintain contact with local emergency services by listening to a battery-powered radio and following their directions
Put on safety gear and sturdy footwear
Carry an emergency supply kit
Lock all doors
Use the local authorities' recommended travel routes
Turn off utilities
Make arrangements for pets.
Individuals who have been forced to leave home should bring their pets along. However, most emergency shelters do not allow owners to bring their pets because of possible health hazards (except for service animals). As such, pet owners must find suitable accommodation options.
It is also essential to ensure that all pets have identification tags that would make them easier to find if they get lost. Residents who leave their pets must ensure that someone has access to their home and can check on their pets. The pets should also be confined to a safe area of the house, with plenty of food and water.
Individuals caught in their vehicles during an earthquake are advised to:
Stop in an open area and switch off the engine.
Avoid overpasses, large trees, electricity wires, bridges, and other things that may fall.
Turn on the emergency break. If the ground underneath the vehicle becomes uneven, the emergency brake will stop the vehicle from rolling back and forth.
Turn on the radio to listen for any crucial alerts.
Fasten seat belts until the earthquake is over.
Proceed with caution after shaking subsides.
Find an emergency supply kit for sustenance till help arrives.
Get out of the vehicle if they smell the gasoline.
After an earthquake, once safety officials declare it is safe to do so, residents in affected areas should inspect the damage, record images, and avert further damage. They must:
Examine property for damage and potential hazards
Perform a damage assessment on all appliances, as well as gas, electric, and water lines, and switch off any utilities discovered to be faulty
Only use matches or turn on any electrical switches after it is confirmed that there are no damages that could cause accidents
Open windows quickly, turn off the main gas valve and get everyone out of the building if there is a gas leak
Report it to the authorities
Clean any prescription, bleach, gasoline, or other combustible chemicals that has been spilled
Assist when necessary
Look out for downed power lines when outside
Prepare for more earthquakes or aftershocks
Wear protective clothing
Avoid beaches because tsunamis can occur after the ground has stopped shaking
Contact insurance provider
Keep pets on a leash or indoors and away from the damage.
Overall, the most crucial components of planning for an earthquake are identifying the risks and preparing for a disaster.