Richter scale (noun, “RICK-ter skayl”)
The Richter scale is a measure of earthquake magnitude. That is, the strength of an earthquake. The bigger the quake, the bigger its magnitude on the Richter scale.
Seismologists Charles Richter and Beno Gutenberg came up with this scale in the 1930s. They rated earthquake magnitude based on the biggest ground vibration — or seismic wave — measured from a quake. The scale was logarithmic (Log-uh-RITH-mik). That means each step up on the Richter scale represents 10 times stronger ground shaking. Earthquakes of about magnitude 3 are just strong enough to be felt. Magnitude 4 and 5 earthquakes are often bad enough to cause damage. The most severe earthquakes ever recorded have been about magnitude 9.
The Richter scale works well for sizing up small earthquakes. But it tends to underestimate big quakes. So, the Richter scale is rarely used today. Instead, scientists use the moment magnitude scale. This is another logarithmic scale for earthquake magnitude. This system uses newer technology to analyze seismic waves in much more detail than Richter’s method. Those details offer a better estimate of the total energy an earthquake releases — and therefore a more accurate earthquake magnitude.
In a sentence
Once a month or so, there is a major earthquake somewhere in the world — one that measures 7 or more on the Richter scale.