Richter scale

Quantitative scale of earthquake magnitude based on the measurement of seismic waves, used to indicate the magnitude of an earthquake at its epicentre. The Richter scale is logarithmic, so an earthquake of 6.0 is ten times greater than one of 5.0. The magnitude of an earthquake differs from its intensity, measured by the Mercalli scale, which is qualitative and varies from place to place for the same earthquake. The scale is named after US seismologist Charles Richter.

An earthquake's magnitude is a function of the total amount of energy released, and each point on the Richter scale represents a thirtyfold increase in energy over the previous point. One of the greatest earthquakes ever recorded, in 1920 in Gansu, China, measured 8.6 on the Richter scale.