The Mississippi River Project
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Mississippi River Project: Day 10

We are in an area below the New Madrid Seismic Zone now.  Randy Cox, a colleague at the University of Memphis in the Earth Sciences department, has mapped large liquefaction features here to the south that do not correlate to the 1811-1812 quakes. 

Liquefaction occurs when the ground shakes and saturated sand (water-filled voids between the sand grains) that is capped from above by a less water-transmissive unit (typically clay), breaks through the layer above.  This happens because the shaking grains of sand initially compact, which reduces the pore space between the grains, and, in turn, raises the water pressure.  This can reduce the strength of the sandy unit and cause water and sand to squeeze up and out of it.

Expressions of liquefaction on the ground surface come in the way of sand blows (burping sand to the surface).  If you were to look at aerial photography of this area it is possible to see hundreds of these features scattered across the landscape.

As this process is most often a shallow phenomenon, the Chirp should be able to pick up such features if they exist beneath our path.  We saw this last year north of Caruthersville, MO, when the Chirp recorded a shallow clay unit fractured in numerous locations.  We interpreted that liquefaction and movement of the sandy unit below allowed deformation in the less permeable unit above.

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Last Updated: 1/23/12