Richter << RIHK tuhr, >> magnitude, is a number that indicates the strength of an earthquake. It is based on data obtained by a seismograph, an instrument that records ground movements. Charles F. Richter, an American seismologist (scientist who studies earthquakes), developed the magnitude numbering system in 1935. The system is sometimes called the Richter scale.
Each number on the scale represents a tenfold increase in the amplitude of waves of ground motion recorded on a seismograph. The seismograph measures the back-and-forth movement of the ground beneath it. Amplitude is the distance this ground moves from its original position during the passage of a wave. Thus, each number represents ground motion 10 times greater than that represented by the next lower number. In an earthquake of magnitude 7, the ground moves 10 times as much as it moves in a quake of magnitude 6.
Calculations based on the Richter scale can show the amount of energy released by an earthquake. Each number represents a release of about 32 times the energy represented by the next lower number. Thus, an earthquake of magnitude 7 releases about 32 times the energy released by a quake of magnitude 6.
To measure the largest earthquakes, seismologists now use another system, the moment magnitude scale. Moment magnitude is based on data recorded by instruments that are more sensitive than those available in Richter’s time. Moment magnitude and Richter magnitude are about the same for earthquakes up to magnitude 7. The highest recorded moment magnitude was 9.5, for an earthquake in the Pacific Ocean near Chile in 1960. The Richter magnitude of this quake was 8.3.
Thousands of earthquakes with a Richter magnitude of at least 2 occur daily. But few earthquakes of magnitude 5 or less cause serious damage. An earthquake of magnitude 7 or more can cause much damage and kill many people.
