Earthquake Magnitude

For many years, the Richter Scale was the most common and familiar earthquake magnitude scale, but as recording instruments have become increasingly sophisticated, more accurate calculations have evolved to determine magnitude. Today, the Richter Scale is seldom used, and scientists prefer to designate any given earthquake with just the word "magnitude," which can represent a number of different scales used in the calculation process.

There are two important things to remember about earthquake magnitude:

  • ​The size of an earthquake increases by a factor of 10 as magnitude increases by one whole number. A magnitude 6.0 earthquake, then, is 10 times larger than a 5.0; a magnitude 7.0 is 100 times larger, and a magnitude 8.0 is 1,000 times larger than a 5.0.

  • The amount of energy released, however, increases by a factor of about 32. Looking at the same magnitudes, a magnitude 6.0 earthquake releases 32 times more energy than a magnitude 5.0; a 7.0 releases about 1,000 times more energy, and a magnitude 8.0 releases about 32,000 times more energy than a 5.0. It is easy to see why magnitude 7.0 and 8.0 earthquakes cause such widespread damage and destruction.
From those numbers it can also be observed that even though a fault may produce a lot of small earthquakes, a larger one won't be prevented.Scientists have also learned that the New Madrid fault system may not be the only fault system in the Central U.S. capable of producing damaging earthquakes. The Wabash Valley fault system in Illinois and Indiana shows evidence of large earthquakes in its geologic history, and there may be other, as yet unidentified, faults that could produce strong earthquakes.