Earthquakes in the SC Low Country and Savannah

Just before 10 pm on the evening of August 31, 1886, residents of the Low Country thought the world was ending. The earth shook violently for over a minute, and in many areas the ground seemed to turn into quicksand, collapsing sturdy brick buildings in an instant. The earth continued to rumble, and a second major shock hit around 4am. Those few who slept did so outside. As the sun rose, the devastation became apparent …

Charleston, SC, after 31 August 1885 earthquake

In Savannah, terrified people ran out into the streets, and one woman leapt from her second story bedroom with her baby in her arms (they survived). But others were not so lucky, and while accurate death tolls were not kept, it was likely near or over 100. Although it took days for the full extent of the event to be known, it was felt over 2.5 million square miles, from Cuba to New York, with structural damage as far away as Kentucky. Every major building in Charleston is said to have been damaged or destroyed. With the recent spread of the newfangled technology of photography, we have a record in images of the aftermath (link goes to collection at the University of South Carolina). In Savannah, a twenty foot long fissure opened on Bay Street, and the facades on several buildings on Broughton Street collapsed.

The violence of the 1886 event came as a surprise to residents of the area – major earthquakes are not frequent. Historical studies reveal three major ruptures: the 1886 quake, one in the 1600’s, and one in the late 1300’s or early 1400’s. There is also evidence of additional earthquakes over the last 6000 years in the sediments of the region. Today we know a lot more about the subsurface geology of the Charleston-Savannah area. The University of South Carolina has a network of seismographs monitoring the region in real time …

Seismograph record for September 27th, 2021,

Just inland of the City of Charleston lies what we know today as the Middleton Place – Summerville Seismic Zone (MPSSZ). It is a complex structure consisting of at least two active faults. Unlike faults in the western US, these faults are buried under hundreds of feet of sediments and there is little evidence to be seen at the surface. While most people never feel them (or think it’s just a passing truck or car wreck on Victory Drive), there are on average between 10 and 15 minor earthquakes a year. By careful analysis of these events, the subsurface geology can be mapped, as seen in this diagram …

From Dura-Gomez and Talwani, 2009 (link goes to research paper).

The earthquake on September 27th was a reminder that deep under the earth there are forces that build over time, and must be released. While not located on a plate boundary, the Charleston area is on a dangerous, deep fault system that will from time to time violently rupture. Simulations show that if the 1886 earthquake were to happen today, there would be at least 45,000 people injured and thousands needing hospitalization for major injuries. Over 200,000 would be homeless. Many roads would be impassable, a third of hospitals in the low country and Savannah would be out of commission. The Beaufort and Hilton Head areas would also be severely impacted, with liquefaction (the ground becoming unstable due to high water tables and shaking) causing major damage and loss of life. While the most severe devastation would be in the Charleston area, many of the major buildings in Savannah would be damaged, with hundreds injured and dozens likely to die, and there would be structure damage across the US East Coast.

Unlike a hurricane, unfortunately while we know where earthquakes happen, we don’t know when the next one will occur. We can only estimate the probabilities. Here is the latest analysis from the USGS National Seismic Hazard Model …

Latest USGS probability of damaging earthquake in the US

So what are the odds? It looks like the chances of a major earthquake on these MMPZ system are about one in 400. By comparison, the chances of your home being severely damaged by a tornado is about 1 in 300, by other thunderstorm related winds about 1 in 180. A tsunami? Hard to say, the worst odds I’ve seen based on a solid scientific study are around one in 47,000, but I think they are much lower, probably over one in 250 thousand. The chances of a home in the Low Country and Savannah area being damaged by a hurricane is about one in 30, destroyed about one in 110. So while this is a risk to be aware of, and the consequences of a major earthquake extreme, there are other things to worry about. It is worth looking at the DHS/FEMA web site for earthquake preparedness (link), and remember that most of the things you do to prepare for a hurricane or other event are similar to that for other disasters.

2 thoughts on “Earthquakes in the SC Low Country and Savannah

  1. Great! First Facebook goes dark, now the threat of earthquake. And hurricane season is alive and well. I’m going to have trouble sleeping tonight!

    Like

    • I thought the FB crash was a good thing … actually got more work done yesterday 🙂

      Looks like hurricane season is winding down, maybe one or two fish storms on the horizon …

      Like

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