SPARTANBURG, S.C. (WSPA) – Earthquakes usually are not top of mind until they happen.

While most earthquakes in the Carolinas are weak, there have been a few strong ones. Charleston had a more than 6.9 magnitude earthquake back in 1886 and a 5.5 magnitude earthquake in Union in 1913.

These earthquakes form the benchmark for what could happen again, but when?

South Carolina Emergency Management Division Derre Becker said the state is always working to stay prepared.

“Unlike a hurricane, earthquakes can’t be predicted. So a lot of what our planning involves is: how do we immediately, or as fast as possible, restore communications to an affected area. How do we evaluate the infrastructure like bridges and buildings that could be used as shelters and how can we get relief aid into an area that is severely damaged by an earthquake,” Becker said.

With an earthquake in the coastal plains, because of its more saturated soil, an earthquake can cause liquefaction. This happens when the water trapped between sand particles gets squeezed out and upward, causing the ground to turn into a quicksand like consistency. Liquefaction can also cause sand blows, where water and sand erupt from the ground leaving a small crater that’s filled in with time.

“We use paleoliquefaction as an asset to figure out the repeatability of earthquakes,” Dr. Talwani said.

Scientists like Dr. Pradeep Talwani, a geophysicist who’s studied earthquakes in the Carolinas since the 1970s, can look at prehistoric sand blows, evident in excavation, to determine when these big events happened. Earthquakes aren’t predictable, but because of this process of looking back at when previous large quakes occurred, they can advise engineers about the repeatability of a strong earthquake.

Just as artic climatologists can look at past events using ice cores, Dr. Talwani and his colleagues look at sand blows from prehistoric earthquakes to know how strong they were and when they happened.

Despite the unpredictability of earthquakes, Dr. Talwani said there is a way to help engineers design buildings better. Bridges, dams and buildings all have to be designed with an earthquake in mind, especially from the coastal plains to the beaches.

“When they’re building a critical facility like a nuclear plant or the Cooper River Bridge, they want to know: what magnitude earthquake do we design it for and how often do we get them,” Dr. Talwani said.

A critical structure for the Upstate is the Jocassee Dam on Keowee River, and Duke Energy is always on standby to make sure it stays strong.

“One of the unique things about Jocassee, Keowee and Bad Creek, which are in this area, is that they’re staffed 24/7,” Ben Williamson, with Duke Energy, said. “If there is a felt seismic event … they’ll feel that and it will trigger an inspection.”

While most of our earthquakes don’t shake many people up, more knowledge about past earthquakes can help us to prepare better for when the next big one happens.