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Sanity -> RE: Giant Crack in Africa Will Create a New Ocean (11/4/2009 2:38:56 PM)
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Something similar may happen in the heartland of the United States one day. Did you know that the largest earthquake in the recorded history of North America occurred in Missouri?
quote:
Recent Midwest Quakes Called Aftershocks from 1800s
The small earthquakes that sporadically rattle the central United States may actually be aftershocks from a few extremely large quakes that occurred in the region almost 200 years ago, according to a new study
The New Madrid Earthquakes, which struck between December 1811 and February 1812, are some of the strongest seismic events ever to occur in the contiguous United States in recorded history. The largest quake is estimated to have been 8.0 in magnitude and was powerful enough to temporarily make the Mississippi River flow backwards. The heart of the seismic activity was near the town of New Madrid, Missouri, close to the Kentucky and Tennessee borders.
The town has shaken with numerous earthquakes since, from tiny ones that don't cause much of a stir, to moderate sized ones, such as a 5.2 quake in 2008. Some scientists suspected that many of these events were really repercussions from the big 1811 and 1812 earthquakes. For one thing, "there's no motion across the fault now, so nothing's going on, but yet there are still small earthquakes there," said Seth Stein, the study's lead author and a professor of geological sciences at Northwestern University. The small quakes also occur on the same fault plane that researchers believe is responsible for the big quakes. Furthermore, the present-day temblors are getting smaller with time, which is a characteristic of aftershocks, Stein said. And when larger quakes do occur, they happen at the corners of the fault section that scientists think broke during the 19th century earthquakes, a pattern that suggests these are aftershocks, Stein told LiveScience.
(Full article here)
quote:
Source of Major Quakes Discovered Beneath U.S. Heartland
...One team of seismologists had thought that high density pillow lavas in the lower crust beneath the New Madrid region could have pulled the crust downward and thereby generated surface stresses that triggered the quakes.
Now, Allessandro Forte of the Université du Québec à Montréal and his colleagues have arrived at a more dramatic mechanism—an ancient, giant slab of Earth called the Farallon slab that started its descent under the West Coast 70 million years ago and now is causing mayhem and deep mantle flow 360 miles beneath the Mississippi Valley where it effectively pulls the crust down an entire kilometer (.62 miles).
"This remarkable localization of flow in the mantle below New Madrid, originating so deep below the surface, was completely unrecognized prior to our work," Forte told LiveScience.
Slabs like this that sink oceanic crust are called subduction zones, and those adjacent to Japan produce intense and damaging seismic activity. "We have discovered an analogous subduction zone, deep inside the Earth below the central Mississippi River Valley," Forte said.
Full article here:
http://www.livescience.com/environment/070502_newmadrid_quake.html
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