Two early November earthquakes hit Central Alabama, so should we expect more?

MONTGOMERY, Ala. (WSFA) - Two earthquakes shook parts of Central Alabama this past weekend. Both were rated magnitude 2.4 on the Richter scale, which is considered minor.

One hit just northwest of downtown Clanton, the other struck to the northwest of Eutaw in rural Greene County. Neither one was felt, but they certainly registered.

With them occurring on consecutive days, does that mean we should expect more in the near future? Is this normal here in Alabama?

While it’s not necessarily rare to have earthquakes -- especially minor ones -- strike in our state, it is a bit more unusual to have two strike on back-to-back days. Going back to the late 1800s, the state of Alabama has recorded 399 earthquakes. That is good for an average of just about three per year.

That’s just the average number. You can have years with less than that, you can have years with more than that and you can have years with many more than three earthquakes across the state.

For example, we’ve only had two so far in 2021, but we saw eight in 2020 and a whopping 17 back in 2019. Each year is different and its own entity. There’s simply no pattern to earthquake activity in Alabama and the Deep South.

The two that struck Central Alabama this past weekend were both on the weaker end of the spectrum, but that isn’t always the case. Alabama has been impacted by earthquakes as strong as magnitude 5.2, 4.9 and 4.6. Those occurred in Irondale, Escambia County and Fort Payne, respectively.

Once you get closer to 3.5 and above on the Richter scale you have a higher probability of having people feel the earthquake. There can even be instances of damage when you approach 4.5 and above. That’s especially true near the quake’s epicenter.

The reasoning behind the earthquake activity in Alabama is the presence and influence of two different seismic zones. The Southern Appalachian Seismic Zone causes the earthquakes across the northern half of the state, while the Bahamas Fracture Seismic Zone directly causes the ones in Southwest Alabama.

Even with our nearly 400 quakes since the late 1800s, there are areas across the Southeast with a much higher earthquake density. That includes northern Georgia, eastern Tennessee, South Carolina, and the New Madrid Seismic Zone along the Mississippi River.

Each of those locations sees substantially more earthquakes than us in Alabama because of where they are in relation to the seismic zones.

Those are also the locations where the “bigger” earthquakes strike; the ones that reach magnitude 5, 6, 7, and 8. It’s those types of earthquakes that can cause much more substantial and noticeable damage and cause a much larger area to experience shaking.

So are we due for “the big one” in the New Madrid region? And what happens in Alabama if that were to happen?

“The historical record and estimated probabilities of earthquakes in the New Madrid Seismic Zone (NMSZ) indicates that we should be prepared and plan for a large magnitude NMSZ event,” says Sandy Ebersole of the Geological Survey of Alabama.

Determining when exactly we’ll see a significant earthquake in that area is impossible, but the chances of it happening in the next century are very much there. I asked Ebersole what the repercussions of such an event would be on Alabama...

“North to central Alabama would experience shaking from a strong (6.0 magnitude or greater) NMSZ earthquake, with potential for minor damage in northern Alabama from a 7.0+ magnitude NMSZ event.”

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