The greatest earthquake risk east of the Rocky Mountains is
along the New Madrid fault system. Damaging earthquakes are much
less frequent than in California, but when they do occur, the
damage can be far greater, due to the underlying geology. The
New Madrid fault system, or the New Madrid seismic zone, is a
series of faults beneath the continental crust in a weak spot
known as the Reelfoot Rift. It cannot be seen on the surface.
The fault system extends 150 miles southward from Cairo,
Illinois through New Madrid and Caruthersville, Missouri, down
through Blytheville, Arkansas to Marked Tree, Arkansas. It dips
into Kentucky near Fulton and into Tennessee near Reelfoot Lake,
and extends southeast to Dyersburg, Tennessee. It crosses five
state lines, and crosses the Mississippi River in at least three
places. Magnitudes are determined by various methods The one of
which most people are familier, is the Richter Scale. The
Richter Scale is a measure of energy released in an earthquake.
It is determined by ground