For millions of people raised in earthquake country, the Richter scale was a constant companion.
Earthquakes were reported on the Richter scale, a mathematical formula invented by Caltech seismologist Charles Richter in 1935 to compare quake sizes. But no one uses the Richter scale anymore in the media or in science. What happened?
The Richter scale was abandoned because it worked best for earthquakes in southern California, and only those hitting within about 370 miles (600 kilometers) of seismometers. These days, scientists detect temblors on the other side of the Earth. In addition, the scale was calculated from one type of earthquake wave, a kind that doesn't help much when measuring truly massive quakes, like Japan's magnitude-9 in 2011. So seismologists created a new scale, called the moment magnitude scale. The moment magnitude scale captures all the different seismic waves from an earthquake, giving a better idea of the shaking and possible damage.
For the rest of the story: http://www.livescience.com/29005-why-richter-scale-no-longer-used.html