Richter Scale Day is celebrated on April 26th of each year.
The Richter magnitude scale (often shortened to Richter scale) was developed to assign a single number to quantify the energy released during an earthquake.
The scale is a base-10 logarithmic scale. The magnitude is defined as the logarithm of the ratio of the amplitude of waves measured by a seismograph to an arbitrary small amplitude. An earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0, and corresponds to a 31.6 times larger release of energy.
Since the mid-20th century, the use of the Richter magnitude scale has largely been supplanted by the moment magnitude scale in many countries. However, the Richter scale is still widely used in Russia and other CIS countries. Also worth noting is that earthquake measurements under the moment magnitude scale in the United States—3.5 and up, on the MMS scale—are still usually erroneously referred to as being measured under the Richter scale in the general public, as well as the media, due to the familiarity with earthquakes being measured by the Richter scale instead of the MMS scale.