Rock and Roll: The New Madrid Fault System Part II: Some Geological History By Stephanie Osborn
Rock and Roll: The New Madrid Fault System Part II: Some Geological History
Excerpted from Rock and Roll: The New Madrid Fault System, ©2017
By Stephanie Osborn
Images in this article are public domain, unless otherwise specified.
This whole collection of writings started off with an email exchange, months ago. Our illustrious hostess was part of the discussion, and expressed interest in my converting the info to one or more blog articles. Then, when the LibertyCon programmers heard about it, they asked me to give a presentation on same, which I did.
The presentation was a full house, and at the end, there was a request for me to convert it to blogs and/or an ebook. I asked how many would like to see an ebook of the material; virtually every hand in the lecture hall went up.
A little over a month later, with additional research under my belt and factored into the manuscript, the book has gone live. And as promised, I am providing Sarah a series of blog articles on the subject. This series of blog articles is only a small fraction of the material contained in the ebook; it may be considered in the nature of a series of informative abstracts of the information contained therein. For additional information, may I recommend that you check out Rock and Roll: The New Madrid Fault System.
Part II: Some Geological History
As the conveyor belt of Earth’s mantle convection floats the crustal plates around, numerous supercontinents have been slammed together and ripped apart through the geological eras.
Some 1 to 1.3 billion years ago, around the beginning of the Neoproterozoic period or possibly a bit before, a supercontinent formed in Earth’s southern hemisphere. Today, geologists call it Rodinia. It is the very earliest supercontinent we can confirm. There were probably others, but we don’t have definitive evidence yet.
Roughly in the middle of Rodinia was a plate geologists called Laurentia. It was the ancient core that came to comprise what we now call North America.
But about 750 million years ago, only ~250-500 million years after it formed, Rodinia began to rip apart. Why?
Because the presence of the big supercontinent insulated the layers below it. A hot spot developed in the mantle underneath, generating an upwelling in the plastic rocks of the mantle, and convection moving away from the hot spot. This produced an upward force under the continent, tending to crack it apart, and “conveyor belts” to carry the pieces away. This is believed to be why all supercontinents ultimately break up.
Gradually Rodinia broke apart, and the new continents moved away from each other. The new continent of Laurentia was put under tremendous stress, as it was pulled from multiple directions—keep in mind, there was considerable friction to deal with. Faults behaved the same then as they do now, and they dragged and ripped at the plate that had been the heart of the supercontinent.
Multiple rifting areas have formed mid-continent due to supercontinent breakups over geologic history. Only one of these is the Reelfoot Rift, around which the New Madrid Seismic Zone and others formed. The Reelfoot Rift is a failed plate boundary; had it torn all the way through, there would be no North American continent as it currently exists.
The Reelfoot Rift has two principal seismic zones and quite a few secondary zones. The primaries are the New Madrid Seismic Zone and the Wabash Valley Seismic Zone.
The New Madrid grabens
The main graben runs right down the Mississippi River central valley. The northeast end runs diagonally from roughly the Land Between the Lakes National Recreation Area to the Shawnee National Forest. The southwest end is somewhat uncertain, but has been identified at least as far as a Mariana-to-Searcy, AR line.
But…there’s more than one graben.
[Map from Van Schmus, W. R., Bickford, M. E., and Turek, A., 1996, Proterozoic geology of the east-central mid-continent basement; in, Basement and Basins of Eastern North America, B. A. van der Pluijm, and P. A. Catacosinos, eds.: Geological Society of America, Special Paper 308, p.7-32. Note the Southern Oklahoma Aulacogen, which extends through TX, OK, NM, CO & UT; it is also a failed rift produced at roughly the same time and for the same reason as the Reelfoot Rift, which houses the New Madrid fault system. Zoom view mine.]
In fact, there are at least four grabens, or fault-block valleys, but unlike most multiple-graben systems, they do NOT lie in parallel. Instead, they all radiate out from a central stress point. One of these grabens, the Southern Indiana, is contiguous with the separately-identified Wabash Valley Seismic Zone. Several others exist, including the Cottage Grove Fault Zone (CGFZ); the Rough Creek Fault Zone (RCFZ); the Ste. Genevieve Fault Zone (SGFZ); and the Shawneetown Fault Zone (STFZ).
States directly affected include:
- Tennessee, and
States indirectly affected include:
- Louisiana, and
The evidence for long-term quake activity along the New Madrid system is mixed. Tree ring growth depicts the 1811-12 quake series, but nothing prior to that, back to medieval times. Yet objects inadvertently buried in previous events—pottery, knapped blades, etc. distinctive to a given period—can be type- and/or carbon-dated, showing evidence of massive quakes in:
- ~900AD, and
Other geological evidence indicates major quake swarms in:
- 3500BC, and
To obtain a copy of Rock and Roll: The New Madrid Fault System by Stephanie Osborn, go to: