M A S T E R P A G E
during flooding conditions. This type of liquefaction most commonly occurs on properties protected by levees,
where rivers can rise to levels above the land surface without actually flooding the land. Most of the New Madrid
Seismic Zone falls into this category, being surrounded by levees that flank the rivers and drainage ditches
throughout the area. Because of this, seismically-induced sand boils became hydrologically active during river
flood stages, and can turn into quicksand and boil again, just as they did during the earthquakes that formed them.
Similarly, tractors, trains, and trucks crossing over sand fissures during times of high water table can
mechanically induce liquefaction, causing highways to sag, railroad tracks to get out of parallel, and farm
equipment to sink into the ground.
Note:
Adapted from Stewart, David, and Knox, Ray,
The Earthquake That Never Went Away: The Shaking Stopped in 1812,
but the Impact Goes On,
Marble Hill, MO: Gatlinburg-Richter Publications, 1993
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