[Rockhounds] New Madrid fault

Mon Mar 23 04:41:21 PDT 2009

Alan wrote

> With regards to the effects of glaciation, the southern-most tip of the
> continental glaciers (the Illinoisian?) reached into southern Illinois. At
> that point, the ice probably thinned to less than 100 feet and stopped
> advancing. Although 100 feet of ice is heavy, I can't see how it would be
> heavy enough to trigger an earthquake. The New Madrid fault zone is an
> unglaciated area.

It's not the weight of the ice-cap in local situations that triggers quakes,
in my opinion.
A continental plate flexes under the weight of a miles thick ice sheet. It
bends down where the centre of the sheet is but UPWARDS at the edges. That
is why the British channel between England and the mainland was probably dry
during the last big ice-age. Much ice in the North and centre of the British
Isles weighed the landmass of it down. When that melted, the land rose but
the surrounding land sank. The isle of White used to be attached to England.

You can try and visualize the effect with a air-mattress. Pump the mattress
for about 3/4. Put something heavy, like a concert piano, in the middle of
the mattress. If you have a hernia or no piano a couple of heavy book will
do. You'll see both end of the mattress rise as you put objects in the
middle and sink if you remove the objects or the plug. (A soft pillow will
demonstrate the effect just as clearly with less effort).

So, what I'm trying to say is that maybe you don't need to be UNDER an
ice-sheet to have it cause earthquakes when it melts or gets thicker. 

Cheers

Axel

> -----Oorspronkelijk bericht-----
> Van: rockhounds-bounces at lists.drizzle.com
[mailto:rockhounds-bounces at lists.drizzle.com]
> Namens erich kern
> Verzonden: maandag 23 maart 2009 9:17
> Aan: Rockhounds at drizzle.com: A mailing list for rock and gem collectors
> Onderwerp: Re: [Rockhounds] New Madrid fault
> 
> 
> There'a book titled, "The New Madrid Earthquakes" by James Penick I read
about ten years
> ago. There are lots of accounts from the newspapers and personal diaries
of the time. A good
> read.
> 
> The Amazon URL is
> 
> http://www.amazon.com/New-Madrid-Earthquakes-James-Penick/dp/0826203442
> 
> According to my USGS quake map, there were three major quakes between Dec.
1811 and
> Feb. 1812 ranging in magnitude from 8.3 to 8.7.
> 
> Erich Kern
> Murrieta, CA
> 
> 
> 
> ----- Original Message -----
> From: Alan Goldstein
> To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors
> Sent: Sunday, March 22, 2009 6:31 PM
> Subject: Re: [Rockhounds] New Madrid fault
> 
> 
> I've read reports regarding studies of prehistoric sandblows, where
> earthquake causes ground liquefaction and geysers of wet sand spewing from
> cracks in the earth. Geologists dig trenches through sediments looking for
> them. I think the evidence indicated a major quake (on the scale of the
1812
> events) recurring on average about every 500 years. Not everyone of them
> would create a Reelfoot Lake. That would depend on whether the fault block
> that shifted was located under the Mississippi (or Ohio) River.
> 
> With regards to the effects of glaciation, the southern-most tip of the
> continental glaciers (the Illinoisian?) reached into southern Illinois. At
> that point, the ice probably thinned to less than 100 feet and stopped
> advancing. Although 100 feet of ice is heavy, I can't see how it would be
> heavy enough to trigger an earthquake. The New Madrid fault zone is an
> unglaciated area. I've read studies that hypothesize that the weight of
the
> Mississippi River sediments on the highly faulted basement rock are
thought
> to keep the system active. Last time I checked, the Mississippi and Ohio
> Rivers are still sending sediment through the fault zone and down to the
> Gulf of Mexico.
> 
> Even if the New Madrid fault zone produced one 7.5 to 8.0 magnitude quake
> every 10,000 years, consider how many "big ones" occurred in the past 700
> million years! There is one fault block in Livingston Co., KY that has
> several thousand feet of vertical displacement!
> 
> Alan G.
> 
> 
> ----- Original Message -----
> From: "Axel Emmermann" <axel.emmermann at pandora.be>
> To: "'Rockhounds at drizzle.com: A mailing list for rock and gem collectors'"
> <rockhounds at lists.drizzle.com>
> Sent: Sunday, March 22, 2009 7:54 AM
> Subject: RE: [Rockhounds] New Madrid fault
> 
> 
> >> I am thinking
> >> statistics here - what are the odds of this happening in this
millennium
> >> (much less this century)?
> >>
> >> Alan G.
> >
> > [Axel] There's an unusual way to find out whether a fault is short-term
> > dangerous or not... If it is, there is probably a name for it in the
tales
> > and myths of the local people. Think about Pompei... in 79 AD  it was
> > destroyed by the eruption of Mount Vesuvius.  We know of that because of
> > the
> > ruins and letters of Plinius the younger.  But what if we hadn't had
> > written
> > testimony? We know that Krakatau is a cataclysmic and recurring volcanic
> > explosion. There have been movies made about it, documentaries, books...
> > still millions of people have chosen to live in the "death zone" after a
> > few
> > years. Were it to blow up now there would be millions of casualties.
> >
> > Still, chances of surviving a large earthquake are better than those of
> > surviving a large volcanic eruption... No lahars, pyroclastic flows,
lava,
> > pressure waves, climate changes, ash rains...
> >
> > If I were looking for an answer about the dangers of a seismic zone, I
> > would
> > go looking in the mythology of the locals and first of all: the place
> > names
> > in the local language If I'm not mistaking that would be in Sioux.
> > Names like: land that dances; land that moves, land that glows (quake
> > lights), shaking land, sand fountain ... Things like that.
> > Reelfoot lake is a good example...
> > http://visitreelfootlake.com/reelfootlegend.htm
> > If cataclysmic earthquakes happen with intervals that span periods
greater
> > than collective memory they will not reflect on the place names. If they
> > happen more regularly you 'll most likely find place names referring to
> > it.
> > Writings can such legends alive for much longer than a few hundred
> > years...
> > Think of Sodom and Gomorra. Those became myth centuries before the
written
> > word became a general tool for recording history. Still, we know of them
> > and
> > archaeology seems to confirm their existence in the distant past.
> >
> > Axel
> >
> >
> >>
> >> ----- Original Message -----
> >> From: "J Bryan Kramer" <codeburner at gmail.com>
> >> To: "Rockhounds at drizzle.com: A mailing list for rock and gem
collectors"
> >> <rockhounds at lists.drizzle.com>
> >> Sent: Saturday, March 21, 2009 11:53 AM
> >> Subject: [Rockhounds] New Madrid fault
> >>
> >>
> >> I thought some may be interested in this:
> >>
> >> <http://www.sciencedaily.com/releases/2009/03/090313145956.htm>
> >>
> >> Do deep subsurface faults always produce measurable surface movement?
> >>
> >> BK
> >>
> >> --
> >> "It often seems to me that the night is much more alive and richly
> >> colored
> >> than the day."
> >>
> >>                       Vincent van Gogh
> >>
> >> J Bryan Krämer       North Florida, USA
> >> photos at: http://pbase.com/photoburner
> >> blog at: http://www.photoburner.net
> >>
> >>
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