Richter Scale

Richter Scale, scale used to assess and compare the intensity of earthquakes. The Richter scale, also known as the local magnitude scale, measures the energy of an earthquake at its centre, or focus, and the rating intensity increases exponentially from one number to the next. It is named after the US seismologist Charles Francis Richter (1900–1985) who devised it in 1935 to rank earthquakes occurring in California. Richter and his associates later modified it to apply to earthquakes anywhere in the world. The Richter scale ranks earthquakes based on how much the ground shakes 100 km (63 mi) from the earthquake’s epicentre, the site on the Earth’s surface directly above the earthquake’s origin. Such disturbances, or Seismic waves, are recorded using an instrument called a seismograph, and it is the energy in these waves that is measured on the Richter scale. Although it is theoretically an open-ended scale, an earthquake magnitude of 9.5 is considered to be the practical limit. Scientists believe that the earth’s crust cannot store enough energy to release a magnitude 10 earthquake.

Some of the effects of the different intensity of earthquake described by the Richter scale are as follows: 3.5 or less have no perceptible effects and are only recorded by seismographs; 3.5–6 are felt generally with effects ranging from relatively slight vibrations to loose objects rocking; 6–7 are quite serious with damage occurring to weak structures—for example, walls fracture and fall and some houses can collapse as the ground begins to crack; 7–8 are considered disastrous as most buildings and bridges are destroyed, railway lines bend, and landslides and flooding can occur; over 8 is considered catastrophic as the effects are characterized by total devastation. (See also Seismology.)

The Richter scale is only one of several scales used to measure earthquakes. Currently, the scale most commonly used by seismologists to rank the effects of earthquakes is the Mercalli scale. This scale measures the effects of an earthquake at different sites and thus the same earthquake has different Mercalli scale values at different sites. The Mercalli scale is marked from I (for barely detectable) to XII (for almost complete destruction).