ELGIN, S.C. (WNCN) – An ongoing earthquake swarm in South Carolina has led the United States Geological Survey to issue an advisory about the chance of larger earthquakes in the future.

The USGS defines an earthquake swarm as “a prolonged sequence of earthquakes that lacks any clear primary event or mainshock, in contrast to an aftershock sequence where a large mainshock is followed by a decaying sequence of (mostly) smaller earthquakes.”

The USGS goes on to say “During an earthquake swarm, the rate of earthquakes is increased, and the probability of larger earthquakes goes up accordingly. This swarm has produced a fairly constant trickle of earthquakes since December 2021.”

A 3.6 magnitude earthquake hit just northeast of Columbia Wednesday, June 29, 2022 at 7:03 PM. The quake was centered near Elgin, South Carolina about 19 miles northeast of Columbia, South Carolina.

Swarms can keep the earthquake rate elevated for a few days to many months and they are impossible to forecast how long a swarm will last. It is also not possible to predict the size of the largest earthquake in the swarm.

While the USGS says the most likely scenario going forward is for the small earthquakes to continue, there is a chance a much larger earthquake could happen.

Map of South Carolina earthquake June 29, 2022

Here are the three scenarios the USGS says are possible:

  1. Scenario One (Most likely, about 95% chance):  Earthquakes continue but with none larger than magnitude 4 within the next month. 
  • The most likely scenario is that the swarm continues as it has over the past months, confined to the region already affected by the swarm. The rate of earthquakes in the swarm is likely to remain the same, if not decrease slightly, over the next 30 days. Smaller magnitude earthquakes will likely be felt by people close to the epicenters. The swarm could also stop completely during this time.
  1. Scenario Two (Less likely, about 5% chance): A larger earthquake (magnitude 4 – 5)
  • A less likely scenario would be a somewhat larger earthquake in the magnitude 4 range. Such an earthquake would be felt over a larger area but would not cause significant damage. An earthquake of this size would be followed by aftershocks that would temporarily increase the number of smaller earthquakes per day. 

  3. Scenario Three (Least likely, less than 1% chance): A much larger earthquake (magnitude 5 or higher)

  • A much less likely scenario, compared with the previous two scenarios, is that the ongoing swarm could trigger an earthquake significantly larger than the M3.6 that occurred on June 29. While this is a very small probability, such an earthquake could have significant impacts on communities nearby and would be followed by aftershocks that would increase the number of smaller earthquakes per day.

The June earthquake is the biggest in the Carolinas since the magnitude 5.1 hit Sparta, North Carolina in August of 2020. The last time South Carolina had an earthquake this big was a magnitude 4.1 near Parkersville in February 2014.

South Carolina is no stranger to seismic activity as there are many fault lines across the state.

The largest quake ever recorded on the east coast was a magnitude 7.0 earthquake near Charleston in 1886.

No one can forecast the exact time or place of any earthquake, including aftershocks or events in swarms. These earthquake outlooks help us understand the chances of having more earthquakes within a given time period in the affected area and are based on statistics from past earthquakes