COLUMBIA, S.C. (WCBD)- A months-long swarm of earthquakes in South Carolina’s midlands region has prompted the United States Geological Survey to issue an advisory about the likelihood of potential future tremors.

The current swarm began on Dec. 27, 2021, when a 3.3 magnitude earthquake was recorded just outside of Elgin, S.C. Since then, the swarm has produced between 0 and 15 earthquakes of magnitude 2.0 or higher each month. The largest event so far this year has been a 3.6 magnitude quake on June 29.

According to the USGS, an earthquake swarm refers to 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.”

Swarms can have the potential to keep the earthquake rate elevated for days and even several months and it is nearly “impossible” to predict when how long an ongoing swarm will last and the size of the largest earthquake in the sequence, the agency noted.

2022 Earthquakes (South Carolina Department of Natural Resources Geological Survey)

While it is not uncommon to experience earthquakes in the Palmetto State– geologists estimate between 10 and 15 quakes happen each year– the swarm has raised concern among residents about whether the state is in store for a major natural disaster.

The largest earthquake within 50 miles of the swarm was a 5.5 magnitude earthquake that hit Union County in 1913, causing damage to brick and stone homes and buildings. The most damaging earthquake, however, was a 7.0 magnitude quake that struck Charleston in 1886.

In response to concerns, the USGS released three possible scenarios that describe whether South Carolina could see a larger earthquake over a one-month timeframe:

  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.

USGS said only one of these scenarios will occur within a particular month, but predicting the exact time or place of any earthquake, including aftershocks remains a challenge.