Intraplate Earthquakes and Seismicity

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  • #1
Astronuc
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http://news.yahoo.com/earths-moving-mantle-leads-earthquakes-unusual-places-100843422.html
Researchers found that intraplate earthquakes — which occur in the middle, instead of at the borders, of tectonic plates — are influenced by convection, or heat-driven movements, of the molten mantle beneath the planet's cold, solid crust.

Although intraplate quakes make up a small percentage of overall earthquakes (98 percent of earthquakes occur at the boundaries of tectonic plates), they have been recorded at strengths of up to magnitude 7.0 and can be among the most disastrous temblors because they're unexpected, . . .
Yellowstone is a relatively hot area.
http://volcanoes.usgs.gov/observatories/yvo/
http://volcanoes.usgs.gov/volcanoes/yellowstone/monitoring_tomography.html

Then there is the New Madrid fault zone in the middle of the US.
http://dnr.mo.gov/geology/geosrv/geores/techbulletin1.htm
 

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davenn
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The NMFZ is an interesting case of intraplate seismic activity compared to say intraplate activity within the Australian continent.

Being that the NMFZ was a rifting plate boundary in the making that failed to continue. A changing tectonic regime within the North American Plate, as a whole, saw the NMFZ change from rifting tectonics to a thrust and strike-slip faulting system.

The Indo-Australian Plate and in particular, the Australian Continent doesn't show any similar significant regions of rifting or thrusting in its geological history, yet has produced a number of significant ( M6 to ~ M 7.2) events over the last ~ 100 years

I will have to do some researching into studies on mantle plumes under the Australian Continent to see if there is any correlation between sites of large and or regular events and plumes ( surely someone has done some seismic tomography research ) :smile:
There are several active regions in Australia of regular small events

Researchers found that intraplate earthquakes — which occur in the middle, instead of at the borders, of tectonic plates — are influenced by convection, or heat-driven movements, of the molten mantle beneath the planet's cold, solid crust.
Honestly ... is that really a eureka moment ? ... I would have thought that would have been more of a foregone conclusion ... particularly in places like "the geysers" area on the CA-NV border, Mammoth Lakes, CA or Yellowstone regions. What do they expect to be the results of rising mantle plumes pushing against the underside of the crust ?



http://www.geo.arizona.edu/geo5xx/geos577/projects/muhlenkamp/tectonics.htm


cheers
Dave
 
  • #4
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Honestly ... is that really a eureka moment ?
There may have been more definitive observations of convection hidden in references from the link --- I haven't chased any down.
that the NMFZ was a rifting plate boundary
Does a failed rift count as a plate boundary? "Chickens:eggs::half dozen:six?" Or, is a semantic distinction of no real significance being made between intra- and inter-plate activity?
 
  • #5
davenn
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Does a failed rift count as a plate boundary? "Chickens:eggs::half dozen:six?" Or, is a semantic distinction of no real significance being made between intra- and inter-plate activity?
no I don't think it does.
What I was trying to get across was that there is a significant reason for the events in the NMFZ and seismically active geothermal hotspots
compared to the intraplate seismically active regions as in Australia ( and probably other parts of the world (that I haven't studied)).
And that is something I consider relevant when looking for other causes of seismicity well away from the plate edges

EDIT: ..... Apart from any deformation of the crust via mantle plumes, the other significant
contributor of intra-plate events would be the natural releasing and reorganising of stresses as a whole across a given plate during its migration.


Dave
 
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From Wiki, https://en.wikipedia.org/wiki/Crater_of_Diamonds_State_Park , "(snip)Arkansas (snip)
(snip)Crater of Diamonds volcanic pipe is part of a 95-million-year-old eroded volcano. The deeply sourced lamproite magma, from the upper mantle, brought the diamonds to the surface. The diamonds had crystallized in the cratonic root of the continent long before and were sampled by the magma as it rose to the surface. The geology of the area and the diamond formation process itself were the subjects of the Ph.D. dissertation of Roland Everett Langford in 1973 from the University of Georgia; in it, he proposed a gas phase reaction from the reduction of carbon monoxide and carbon dioxide in the upper mantle. The dissertation was on display at the state park for many years. The lamproite diamond source is unusual, as almost all diamonds are mined from kimberlite and from alluvial deposits of diamonds weathered from kimberlite. The most prominent lamproite diamond source is the Argyle diamond mine in Australia."
studies on mantle plumes under the Australian Continent
Might be a pointer (no, not the shark) for you.
 
  • #7
davenn
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speaking of sharks .... a 6 and a bit metre great white was videoed offshore northern NSW state today 18+ freakin' feet !! very scary

yes, I am aware of the Kimberlite type diamond deposits in Oz. But of course they are reasonably old formations ... stated above 95 million yrs etc

keeping on the original thread topic ... am more interested in younger activity to ongoing current activity

another interesting article ....
Mantle plumes crack continents
http://www.sciencedaily.com/releases/2014/09/140904103807.htm
was also posted in physics.org
http://phys.org/news/2014-09-mantle-plumes-continents.html

a couple of snippets from another site ....

Most of the Australian volcanoes active in the last 35 million years have developed from plumes or hot spots
Australian volcanoes are either dormant or extinct. The most recent volcanic activity on the Australian mainland was the eruption of Mount Gambier volcano in South Australia around 2900 BC.
this may be interesting.....
http://austhrutime.com/superplumes_mantle_plumes_subducting_slabs_multiscale_seismic_tomography.htm


there's more stuff out there, will have to do more searching and reading :smile:

cheers
Dave
 
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keeping on the original thread topic ... am more interested in younger activity to ongoing current activity
"In the model, the deformations are created quickly from a geological point of view. Rift systems several kilometres deep and more than a thousand kilometres long can form after "just" two million years." (from Davenn's link http://phys.org/news/2014-09-mantle-plumes-continents.html#jCp )

This has me "drooling" over possibilities for hunting "fossil" rifts
 
  • #9
davenn
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This has me "drooling" over possibilities for hunting "fossil" rifts
That made me giggle :smile: ( in a good way)

mite make for a good MSc or PhD study topic

"The implications of reactivated fossil rifts due to mantle plumes" :wink:


Dave
 

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