Geology/New Madrid Fault
There was a report this week on a Shreveport television station about the New Madrid Fault. It said there could be an earthquake within the next 50 years - do you agree or disagree?
Well, faults do tend to occur with some regularity, but only if the stresses acting to cause them are constant.
What I mean is that whatever forces along the New Madrid fault need to be fairly constant in order to cause the rocks to fail with any predictability.
The NM fault falls along the failed third arm of the Mississippi River embayment.
If you look at a map of the gulf coast, the coastline running east of New Orleans is the right arm of the triple junction, the coast running west is the left arm and the Mississippi valley is the "failed" third arm. In other words when North America was breaking away from the massive continent that once existed, the break began as a triple junction one arm running into the continent center did not completely rift, but rather just formed a fault valley.
You see the same thing along the Horn of Africa where the Great Rift Valley formed which is similar to the Mississippi Valley. You see the same thing along the coasts of other continents.
So, if there are still tectonic forces working and they are fairly constant, then there might be some predictability to when another major fault will occur. The last big one was in the early 1800's before the area was heavily populated. Eye witnesses said the prairie rolled and heaved with waves like those on the ocean. Sand volcanoes formed along the Mississippi (water trapped between saturated sand lenses was freed and shot to the surface looking like mini volcanoes, a similar kind of thing you see at the beach when you wiggle your toes and water bubbles up and your food slowly sinks into the sand.) Even the Mississippi river changed its course.
Records show continuous seismic activity in the area which says forces are still at work, but when you have a lot of small quakes it makes the likelihood of a large one decrease as it prevents the build up of stress. Quakes occur when rocks along a fault bind up or lock against each other, allowing forces to build, then release suddenly like a stretched rubber band. The rocks slide by one another or up and down in a massive release of energy. It is not at all like you see in the movies. The rocks jerk and wham! They move suddenly as the build up forces exceed the strength of the rock to continue to bind and they spring into motion. The damage is caused by the movement of the soil lying over the bedrock where the movement takes place. If the soil is water saturated, it wobbles and shakes like a massive cube of jello and the resonance movement is what is so devastating to structures. Structures are built to withstand vertical compressive force, to support themselves, not lateral forces. So moving them side to side causes them to collapse. Earthquake proof buildings are constructed to withstand those lateral movements. However I do not think St. Louis had many quake proof buildings.
Now do not believe the forecasts of the US splitting along the Mississippi River, I saw one map predicting this. When something like this is likely, it is slow and the crust thins in that area. It is called Basin and Range physiography. The crust thins, breaks and fault blocks sink leaving high blocks on either side which form mountain ranges bounding the down faulted valley. This is actually happening in the Rift Valleys of Nevada and New Mexico. The crust is actually thinner in those areas, due to stretching of the crust of the continent. Thermal springs are common because the heat of the mantle rocks heats the ground water and it comes back to the surface has hot springs.
I took a recent trip to New Mexico and in the north east corner there are over 120 extinct volcanoes relics from a basin and range type event which resulted in a lot of volcanism, as late as 10,000 years ago. My point is, if the Mississippi valley was going to result in the splitting of the continent, you would see massive volcanic activity in the area. The faulting is due to compressive forces, not tensional or pulling forces.