Historical December 1983 report or notice. Original dates, prices and contacts describe the source period; current availability has not been established.
The current vogue in geology is called “plate tectonics.”’ What it means is the land masses above water are floating on heavier molten liquid(s) below them.
Even the ocean basins are changing shape and position as the continental plates float and jostle in a kind of bumper-continents. Last August was the centenary anniversary of the destruction of the island called Krakatau or Krakatoa.
In 1883, that island between Sumatra and Java exploded sending tons of ash into the sky cooling the entire north temperate zone by nearly a full degree centigrade on average. Such an anniversary calls to mind the coming bicentennial of the earthquake at New Madrid in 1811-12.
The New Madrid fault is only now being understood.
It seems the interior part of the North American continent is thought to be the oldest part of the plate we are floating upon.
One of the younger sections is the coastal plain and the Appalachian Mountains.
This younger section still grinds against the older part, particularly just north of New Madrid.
The boundary between the old section and the young southern section is north of New Madrid, above the mouth of the Ohio River.
Some fault maps suggest it may be nearer St. Louis than New Madrid! Geologic history suggests that the Ohio River originally entered the Mississippi below Natchez, Mississippi some 650 kilometers (400 miles) below where it enters now at Cairo, Illinois.
In the New Madrid area, some 70 kilometers (43 miles) below Cairo, changes in the earth caused the Ohio to change course to the point where it enters the Mississippi today. Of . course the Mississippi’s course was changed too.
The central sections of floating continental plates are generally some of the most stable areas on the earth. Called cratons, they have few quakes.
When they have them, however, it is because some part of the craton is moving with rock of a different consistency which has some velocity in a slightly different direction. That is preciselythe problem at New Madrid.
The force of the three major quakes at New Madrid during the winter of 1811-1812 all exceeded the San Francisco earthquake of 1906.
The difference was the amount of population and the ability of scientists to reach the quake site.
It so happened that an explorer-scientist was on the Mississippi at New – Madrid in late 1811. John Bradbury left us a stirring account of the backwards flow of the Mississippi, the movement of the bank of the river, and the terror he and his French canoemen felt when the earth moved carrying the river, the canoe and their supplies all over the landscape.
The three main shocks of the New Madrid quake, between December 1811 and March 1812, are all thought to have been at least 8.6 on the Richter scale.
The San Francisco quake shock was 8.3 on the scale.
Because the Richter measuring tool is geometric, a few points change is a drastic amount of force.
The rock around the New Madrid fault area is more conducive to damage than that around the San Francisco area. if two earthquakes of equal value hit both places simultaneously, the areas of damage would be considerably different.
In the New Madrid area, the damage area would be substantially larger because the rock transmits the seismic waves and forces more easily.
In California, the major area of damage would not even leave the state.
In Missouri, the major area would include nine states. Minor damage would include almost the entire eastern half of the country and westward into Kansas and Nebraska.
Thus, the peculiar geologic characteristics of the central Mississippi Valley would mean earthquake damage would be extremely significant on all the major population centers west of the Rocky Mountains.
All of this started because of the 100th anniversary of the volcanic eruption at Krakatau. Seismic geologic activity is associated with earthquakes and volcanoes.
These events rearrange the surface of the earth and all life on that surface.
The current look of the Mississippi valley is comparatively modern — less than 25,000 years ago it was substantially different.
The New Madrid fault is expected to produce quakes of the 8.6 Richter level every 600 to 1,800 years.
We probably don’t have much to worry about!
Originally published in The Paper, December 1983.
Read this article in the original newspaper issue.
Archival transcription note: Plate-tectonic explanations, New Madrid earthquake magnitudes and recurrence forecasts are the author’s 1983 account and should not be used as current scientific or safety guidance without independent verification.
Original source: SD_Times1983_12.pdf, printed page(s) 12; PDF page(s) 12.
