USGS issues an earthquake advisory for parts of South Carolina

The United States Geological Survey (USGS) issued an earthquake advisory for the Midlands of South Carolina after the recent swarm of earthquakes in the area.

USGS Earthquake Hazard Map

The swarm started in late 2021 (December 27 with a magnitude 3.3 earthquake), continuing into 2022 with several magnitudes of 2.0+ earthquakes with a few exceeding 3.0. The largest earthquake so far was a magnitude 3.6 on June 29, 2022. A swarm of earthquakes is known as a prolonged sequence of earthquakes that lacks any clear primary event or mainshock according to the USGS. Earthquake swarm longevity is hard to predict but can last for months. As equally hard to predict is the size of the earthquakes.

During earthquake swarms, the probability of larger magnitude earthquakes can increase along with the frequency of earthquakes. Because of this recent swarm, the USGS suggests there's a 95% chance the swarm continues with small earthquakes (generally less than magnitude 4.0). There's also a 5% chance of a magnitude 4.0-5.0 earthquake and just under a 1% chance for an earthquake larger than 5.0.

Earthquakes aren't new to this area. Occasional small, scattered earthquakes, can and have occurred. The largest earthquake within 50 miles was a magnitude 5.5 back in 1913 in Union County. In 1886, a magnitude 7.0 earthquake (the Charleston earthquake) rocked and damaged the state. This earthquake was just under 90 miles away from the ongoing swarm.