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 motion on seismograms. An earthquake has only one Richter magnitude.
What do the numbers on the Richter Scale tell us? Each unit of the Richter Scale is a tenfold increase in the relative size of an earthquake. A magnitude 6.0 is ten times the size of a magnitude 5.0, and one hundred times the size of a 4.0. But energy release is a different matter. Each unit up the Richter Scale is around a 32 times greater release of energy. A magnitude 6.0 releases 32 times more energy than a mangitude 5.0, and about one thousand times more energy than a magnitude 4.0
The amount of energy released in a small earthquake is not enough to prevent a large one from occurring. A million magnitude 2.0 earthquakes would release the same amount of energy as one magnitude 6.0 quake. 32,768 magnitude 2.0 earthquakes would release the same amount of energy as one magnitude 5.0
Of greatest concern in the near future, then , are the 6.0 to 6.5 events. Damaging earthquakes in this magnitude range are possible within the lifetimes of our children. Two have occurred since 1811-1812, one in 1843, and another in 1895.
Many things can be done to protect ourselves. Education, preparedness planning, and proper building construction are proven means to minimize the deaths, injuries, and economic losses due to earthquakes. Northern California and Armenia recently experienced 6.9-7.1 earthquakes.Northern California was prepared, Armenia was not. In northern California 62 people died and there were more than $6 billion in losses. In Armenia over 25,000 people died and losses were greater than $20 billion. The central United States is more prepared than Armenia, but not nearly as well prepared as northern California.
The choice is ours. We can get ready and reduce our losses, or we can do nothing, and suffer the full consequences of a damaging earthquake. We need to continue to plan, to build better buildings, and make sure that earthquake preparedness becomes a part of all our lives. We cannot prevent the coming of an earthquake, but we can reduce the effects.