[Rockhounds] New Madrid fault

Mon Mar 23 18:04:20 PDT 2009

>From what I remember, you'd have to get pretty far north to find evidence of 
ice that was really thick. I remain doubtful that isostatic rebound would 
trigger quakes 300 - 500 miles away. I'm sure you can find a structural 
geologist with the Illinois State Geological Survey who could answer that 
question with more authority that me! I've not read or heard about any 
measurable glacial rebound in Illinois - Indiana - Ohio. The ice mass was 
not real thick until you go into Canada. Hudson Bay has the fastest rebound 
in North America. There are other major basement fault zones in the midwest 
U.S. and there is little evidence that any of them have had earthquakes 
associated with them. Possible exception: Wabash Valley fault zone that had 
the quake back last April. You'd have to ask the experts, not me!

Alan


----- Original Message ----- 
From: "Axel Emmermann" <axel.emmermann at pandora.be>
To: "'erich kern'" <efkern at earthlink.net>; "'Rockhounds at drizzle.com: A 
mailing list for rock and gem collectors'" <rockhounds at lists.drizzle.com>
Sent: Monday, March 23, 2009 7:41 AM
Subject: RE: [Rockhounds] New Madrid fault


> 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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>
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