Richter , Charles Francis

(1900–1985) American seismologist

Born in Hamilton, Ohio, Richter was educated at the University of Southern California, Stanford, and the California Institute of Technology, where he obtained his PhD in 1928. He worked for the Carnegie Institute (1927–36) before being appointed to the staff of the California Institute of Technology. He became professor of seismology there in 1952.

Richter developed his scale to measure the strength of earthquakes in 1935. Earlier scales had been developed by de Rossi in the 1880s and by Giuseppe Mercalli in 1902 but both used a descriptive scale defined in terms of damage to buildings and the behavior and response of the population. This restricted their use to the measurement of earthquakes in populated areas and made the scales relative to the type of building techniques and materials used.

Richter's scale is an absolute one, based on the amplitude of the waves produced by the earthquake. He defined the magnitude of an earthquake as the logarithm to the base 10 of the maximum amplitude of the waves, measured in microns. This means that waves whose amplitudes differ by a factor of 100 will differ by 2 points on the Richter scale. With Beno Gutenberg he tried to convert the points on his scale into energy released. In 1956 they showed that magnitude 0 corresponds to about 10¹¹ ergs (10⁴joules), while magnitude 9 equals 10²⁴ ergs (10¹⁷ joules). A one unit increase will mean about 30 times more energy being released. The strongest earthquake so far recorded had a Richter-scale value of 8.6. In 1954 Richter and Gutenberg produced one of the basic textbooks on seismology, Seismicity of the Earth.