This might also be of interest. Now, personally I have done estimates and I get something like 9.6 magnitude for the 2-7-1812 quake and 9+ for all the
other quakes then. Where they estimate 8.0-8.8 for the quakes back then in the source below in the link, with the most commonly cited historical
estimate for the old quakes actually being 8.0-8.9 (the new USGS estimates are just misinfo and disinfo). I believe 9.6 is the actual figure for the
biggest quake, but nonetheless.... This source is a good way to understand the main problem of New Madrid. What is most important is the shaking
intensity, the Mercalli Scale.
Note the Roman numerals in the link below. I have been looking for a good source like this online that had the intensity scales of great historical
earthquakes in terms of damage. This shows it. The Roman numerals are for the Mercalli Scale of intensity. This is not the energy release estimation
(which keep in mind is speculative for quakes back then and not actually measured), but the intensity of the shaking.
The highest you can go to on the intensity scale is 12. Just so everyone understands what this means:
Richter Magnitude - Typical Maximum Modified Mercalli Intensity
1.0 - 3.0 - I
3.0 - 3.9 - II - III
4.0 - 4.9 - IV - V
5.0 - 5.9 - VI - VII
6.0 - 6.9 - VII - IX
7.0+ - VIII or higher
Modified Mercalli Intensity Scale
- Not felt by many people unless in favorable conditions.
- Felt only by a few people at best, especially on the upper floors of buildings. Delicately suspended objects may swing.
- Felt quite noticeably by people indoors, especially on the upper floors of buildings. Many do not recognize it as an earthquake.
Standing motor cars may rock slightly. Vibration similar to the passing of a truck. Duration estimated.
- Felt indoors by many people, outdoors by few people during the day. At night, some awakened. Dishes, windows, doors disturbed;
walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rock noticeably. Dishes and windows rattle alarmingly.
V. Rather Strong
- Felt outside by most, may not be felt by some outside in non-favourable conditions. Dishes and windows may break and large
bells will ring. Vibrations like large train passing close to house.
- Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken; books fall off shelves; some
heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight.
VII. Very Strong
- Difficult to stand; furniture broken; damage negligible in building of good design and construction; slight to moderate in
well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken. Noticed by people driving
- Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse.
Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture moved.
- General panic; damage considerable in specially designed structures, well designed frame structures thrown out of plumb. Damage
great in substantial buildings, with partial collapse. Buildings shifted off foundations.
- Some well built wooden structures destroyed; most masonry and frame structures destroyed with foundation. Rails bent.
- Few, if any masonry structures remain standing. Bridges destroyed. Rails bent greatly.
- Total destruction - Everything is destroyed. Lines of sight and level distorted. Objects thrown into the air. The ground
moves in waves or ripples. Large amounts of rock move position. Landscape altered, or leveled by several meters. In some cases, even the routes of
rivers are changed.
Now, in this thread there have been sources that have been shown that put it as much lower than that for those quakes 200 years ago, which I knew was
not accurate and was part of the USGS intentionally trying to downgrade the threat recently. It had always been said throughout the years that the New
Madrid quakes of the early 1800s were the biggest ever known in recent times in terms of intensity. And that they were cataclysmic near the
Well, here is a source showing that at the link below. Like I said, the USGS is trying to downplay this intentionally. The intensity damage of all the
1811-12 quakes was 12 on the Mercalli Scale. To put this in proper perspective, it was 8 Mercalli for the 2011 Japanese quake, and 9 Mercalli for the
2010 Haiti quake.
We are talking 12 for New Madrid by comparison. So this really is the thing that people need to be aware of and to understand. If there is going to be
an event in that region, it just is not safe there, due to the incredibly severe shaking intensity and due to the buildings not being set for proper
earthquake codes. Think of what happened in Haiti to the buildings.
The sediments of the area work as an amplification force and thus give more power to the quakes. That causes the dreaded liquefaction of the ground
and the rolling effect, which topples buildings. Basically, it means that any building near the epicenter of the quake, that is not built to withstand
very large earthquakes is going to fall down. Which means cities like Memphis are in huge trouble if it happens. So hopefully this puts that argument
to rest and people understand if they live near this fault that the shaking intensity will bring down any normal structure. 12 Mercalli means nothing
can withstand it. It is because once the ground liquefies and then the rolling back and forth motion begins, the buildings fall like a deck of stacked
cards that are flicked by a finger.
Major Historical Earthquakes
Notable earthquakes in history
year affected area magnitude* intensity
1811–12 New Madrid, Mo. (U.S.) 8.0 to 8.8 XII
edit on 28-3-2011 by Red Cloak because: (no reason given)