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Author Topic: New Madrid Seismic Zone Activity  (Read 37403 times)

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Offline Thundersnow

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Re: New Madrid Seismic Zone Activity
« Reply #60 on: April 03, 2022, 09:52:20 PM »
I would be interested. Geology and tectonics are fascinating.

Offline bugalou

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Re: New Madrid Seismic Zone Activity
« Reply #61 on: November 06, 2022, 01:19:31 PM »
Looks like this paper is easily available now that describes what I believe is the cause for seismicity in the NMSZ.

Its a fairly new theory that has really started to take root in the past couple decades. I have read countless papers on the subject and this makes the most sense to me.  All the theories note the presence of the reelfoot rift which is a failed continental rift from the past where the North American plate tried to break apart from both tectonic stress and passing over the Bermuda hotspot.  It is fairly typical for a continental plate to have these scars and others exist like the mid continent rift under the middle of NA.  The question has always been why the NMSZ creates such large, regular Earthquakes where all these other rifts aren't as nearly powerful and frequent. If the theory of continental compression from the North Atlantic ridge spreading being the cause is true, it should cause a fairly even spread of these events in these areas but it doesn't. Same goes for the idea of glacial rebound where the plates rise slowly with the weight of the ice age glaciers no longer present.

In this theory how ever it is thought an ancient chunk of the Farralon plate is sub ducting nearly vertically into the mantle right below the reelfoot rift. Well, I should say its not just thought, they have proven it with seismic tomology. This downwards tugging accounts for the stress build up mechanism in the faulted basement rocks of the NMSZ. More over there is evidence being shown in other papers this stress is present further south and west than we have typically identified the NMSZ being.  There is evidence in sand blow formations of very strong quakes occuring as far as SE Arkansas with at least two documented accounts in the past 5000 years being found. This could put a whole much larger area of the midsouth at risk than previously thought and its totally possible a major quake with an epicenter just a few miles from down town Memphis is totally within the realm of possibilities.  Monitoring the stress build up is very hard though in this scenario as the area of focus is under hundreds of feet of alluvial soil from the MS, AR, and TN rivers.

Of course a major EQ is still very unlikely on these geological time scales in our lifetimes but lets just say I still have a earthquake policy on my house.

« Last Edit: November 06, 2022, 01:28:52 PM by bugalou »

Offline ChrisPC

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Re: New Madrid Seismic Zone Activity
« Reply #62 on: November 07, 2022, 12:27:26 AM »
That theory also explains a dormant underground volcano under Jackson, MS. I grew up near there and never even knew about it until this year! It’s right under the state coliseum and fairgrounds. It actually was a huge deposit of food-grade CO2, until natural gas was found mixed in recently. There’s also another one just north of Yazoo City, but it didn’t have the CO2 deposit.

Offline bugalou

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Re: New Madrid Seismic Zone Activity
« Reply #63 on: November 07, 2022, 01:43:39 PM »
That theory also explains a dormant underground volcano under Jackson, MS. I grew up near there and never even knew about it until this year! It’s right under the state coliseum and fairgrounds. It actually was a huge deposit of food-grade CO2, until natural gas was found mixed in recently. There’s also another one just north of Yazoo City, but it didn’t have the CO2 deposit.

Correct. The Jackson MS volcano is theorized to be from when the NA plate was passing over the Bermuda hotspot and it flared up in activity.  There is support show that there may be another spot NW of Jackson under all that delta soil where another Volcanic fossil is present from the same process.

 

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