Definition: A logarithmic scale used to measure the size of earthquakes. Each whole number difference (i.e. 5.4 to 6.4) represents an increase in 31 times the energy released by a quake. The Richter scale has been modified and now, other scales are often used to measure earthquakes.
From the USGS: "Earthquakes with magnitude of about 2.0 or less are usually called microearthquakes; they are not commonly felt by people and are generally recorded only on local seismographs. Events with magnitudes of about 4.5 or greater - there are several thousand such shocks annually - are strong enough to be recorded by sensitive seismographs all over the world. Great earthquakes, such as the 1964 Good Friday earthquake in Alaska, have magnitudes of 8.0 or higher. On the average, one earthquake of such size occurs somewhere in the world each year. The Richter Scale has no upper limit."
