The Carolinas have been all shook up by earthquakes this summer. Is a big one next?
From the Lake Norman area north of Charlotte to the Midlands of South Carolina, small earthquakes have been reported across the region this summer.
While most have been relatively minor, some folks have reported feeling the earth move.
And the events have raised questions for many residents about whether a more powerful earthquake could happen in the area and what the overall risk of earthquakes is in the Carolinas.
Here’s what to know about the recent string of earthquakes, the area’s history with earthquakes and what the risks are of a larger earthquake in the region:
Recent earthquakes in the Carolinas
Multiple small earthquakes have been reported in North Carolina and other parts of the region over the summer.
A magnitude 1.8 earthquake was reported near Lake Norman in mid-August after two earthquakes with magnitudes of about 2 were reported about 50 miles northwest of Charlotte within a week in May.
“There were three small earthquakes in western North Carolina over the last week,” Duke professor Henri Gavin, an expert in earthquake engineering, said Monday. “In 2021 there were about 30 such earthquakes — roughly one every two weeks on average. If 2021 was a typical year for such events, then the chance of there being three earthquakes in one week is about 15%. That’s about the same as rolling a ‘7’ in one roll of two six-sided dice.”
And the U.S. Geological Survey reports that South Carolina has been in the midst of a “swarm” of earthquakes — “a prolonged sequence of earthquakes that lacks any clear primary event or mainshock.”
The largest related earthquake so far, per the USGS, was a magnitude 3.6 earthquake in late June.
When you’ll feel an earthquake
Some earthquakes are minor enough that they largely go unnoticed by the general public, but experts say more than just the magnitude of the earthquake determines whether or not it’s felt.
“The magnitude, location, and depth of an earthquake, and overlying soil conditions determine how widely and strongly any particular event can be felt,” the USGS says. “Typically, people report feeling earthquakes larger than about magnitude 3.0.”
What are the odds of a major earthquake in the Carolinas?
Just because relatively small earthquakes have been reported in the region doesn’t mean that a larger, potentially damaging earthquake is coming, according to Gavin.
“To the best of my understanding, this cluster of recent earthquakes can not be used to indicate an increased risk of a large pending earthquake without additional regional geophysical modeling,” he said.
The USGS said in its latest statement on the ongoing earthquake swarm that the “most likely” scenario — “about 95% chance” — is that the earthquakes will “continue but with none larger than magnitude 4 within the next month.”
“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 …,” the USGS said. “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.”
Events in other parts of the Carolinas and even the rest of the Southeast can impact Charlotte, Gavin noted.
“Seismic hazards across North Carolina are affected by potential earthquakes occurring within and outside our state,” he said.
This story was originally published August 23, 2022 at 1:56 PM with the headline "The Carolinas have been all shook up by earthquakes this summer. Is a big one next?."
