One of my idiosyncratic sets of posts are those before various PC(USA) General Assembly meetings looking at the geologic hazards for the host city. So you are thinking “What could go wrong in St. Louis?”, besides the Big Muddy flooding of course. Well, geologically it is quieter than our last venue which was right between an active volcano and a megathrust, but it still has its own unique risk.

It turns out that St. Louis sits fairly close to the north end of the New Madrid Seismic Zone, a set of structures famous for four large earthquakes over the winter of 1811-1812. These events are thought to be in the upper half of the 7 magnitude range, possibly into the low 8’s. Yes, massive earthquakes in what was then the middle of nowhere. There was a bit of civilization around then and they tell harrowing stories, including a short stretch of the Mississippi River flowing backwards for a few hours. And the original town of New Madrid… it is submerged in the river. And for the record, I have some experience in the area having published a couple of papers on my work there. ( Paper 1, Paper 2)

The good news is that from a human time scale these are rare events, something that happens about every 500 years, or maybe every 1000 years, and we are only 200 years out from the last ones. But there is a low level of activity around as well, mostly in the bootheel region and around Memphis. This is my favorite map to keep an eye on it.

The real concern of course is not the earthquakes themselves but the seismic strength of the buildings in the area. You can see from the seismic hazard maps for building codes that Memphis is a level 3 while St. Louis is a level 2A. (And for reference, my house in California is solidly in a highest level 4 zone.) But these are relatively new and many historic buildings don’t have the seismic reinforcing that newer buildings have. So something to keep in mind.

So, look forward to seeing you in St. Louis and let’s be careful out there.