RICHTER, CHARLES FRANCIS

(b. Hamilton, Ohio, 26 April 1900; d. Altadena, California, 30 September 1985), geology, seismology.

Carl Richter was one of the key figures in developing the new field of seismology in the first half of the twentieth century, most notably through inventing the magnitude scale used to describe the size of earthquakes, and in investigating the seismicity of the world, especially of southern California.

Early Years In 1909 Richter’s family (his mother Lillian Richter, his maternal grandfather, and an elder sister) moved to Los Angeles, in southern California, where he was to spend his whole career. Richter later credited his grandfather with being one of the major influences on his upbringing. He began college at the age of sixteen; he began his undergraduate work at the University of Southern California and at Stanford University in chemistry, but changed to physics because of his clumsiness with equipment. After graduation he suffered a breakdown, but, remaining interested in science, later enrolled in the graduate physics program at the California Institute of Technology (Caltech), where he obtained a PhD in theoretical physics, on the quantum theory of electron spin, in 1928. Seeking a job that would keep him around Caltech, in 1927 he became an assistant in H. O. Wood’s program to map earthquakes in southern California, which had been set up by the Carnegie Institution of Washington in 1921. In 1927 the earthquake program became a joint one with Caltech, and was housed in the new Seismological Laboratory a few miles from the campus; Richter, along with Wood and instrumentalist Hugo Benioff, became one of the small group who worked there to build the first network of seismometers in the United States specifically designed to record local earthquakes.

Seismological Survey A major reason for setting up this network was to detect and locate smaller earthquakes in Southern California, in the expectation that the locations of small earthquakes would be a clue to larger ones. For the resulting list of earthquakes not to be misleading, though, it had to somehow indicate if earthquakes were small or large. Earthquake size had usually been described using the intensity of shaking felt by people, an approach that would not work for earthquakes too small to be felt and those in desert areas or offshore. Seeking a method that would use the instrumental data, Richter took the technique of plotting ground motion against distance, presented by the Japanese seismologist Kiyoo Wadati in 1931, and transformed it to produce the motion at a standard distance from measurements made throughout the network; the logarithm of this standardized value gave the relative sizes of earthquakes, a number which Richter, at Wood’s suggestion, called the earthquake magnitude—in part by analogy with the usage of this word in astronomy. Earthquakes were assigned magnitudes starting with the first list produced, in 1932, though the procedure was not published until 1935.

In 1930 Caltech hired Beno Gutenberg, then perhaps the world’s leading seismologist, whose academic advancement in Germany had probably been hindered by his Jewish background. One important reason for Caltech to hire Gutenberg was to provide expertise in using the data being collected by the network for more purely local study. Gutenberg and Richter established a working relationship that was to extend over more than two decades. While at the start they were employed by different institutions, this ended in 1937 when the seismological program was taken over by Caltech and Richter was put on the faculty. For more than ten years after Gutenberg’s arrival, they pursued the combined problem of improving the estimates of travel times for different seismic waves, and the location of earthquakes throughout the world, particularly deep shocks. They were aided in this by the new and more sensitive seismometers developed by Benioff. A result of this effort was a complete set of travel times for different waves, useful for understanding the structure of Earth.

During this time they also extended the magnitude scale from the local area of Southern California to the whole world, first for shallow earthquakes and later (in work by Gutenberg) for deep ones. This extension was put to use in creating the first global catalog of earthquakes in which the sizes and locations were determined entirely from instrumental data collected worldwide, and so was not biased by population distribution. The first version of

this (The Seismicity of the Earth) was published in 1941; subsequent extensions appeared in different editions to 1954. These catalogs showed the concentration of large shocks into relatively narrow belts around Earth, and the even tighter concentration of deep earthquakes into a few limited regions: both results were an important element in later discussions leading to plate tectonics. Another result of this analysis, and of the listing of earthquakes in Southern California, was the Gutenberg-Richter relation between magnitude and rate of earthquake occurrence. This relationship is that as the magnitude of earthquakes decreases by one unit, the number of earthquakes increases by a factor of about ten: small earthquakes are much more numerous than large.

Throughout his career Richter remained active in the regular work of analyzing seismic records from local and distant earthquakes, with a commitment to maintaining the quality of the record of local shocks. This remained true even through World War II, when, after a short period of assisting with weapons work, he returned to seismology, providing advice on seismic hazard and current earthquakes to the U.S. authorities. As it happened, following the war seismic activity in Southern California increased, and Richter studied several larger earthquakes that occurred between 1946 and 1952. His care for the continuity of recording also kept him in California with few interruptions, the longest being a one-year sabbatical in Japan in 1959–1960.

Public Spokesman After Wood’s early retirement in 1934, Richter had become the usual Seismological Laboratory spokesman to the press about current seismic activity, a role he enjoyed. This led him, especially in the late 1950s and the 1960s, to become a persistent advocate for improved seismic safety in California: he spoke to many public organizations, and made efforts to get civil defense authorities to treat natural disasters as part of their remit. This interest in seismic hazard also led to research on how to best describe relative risk. After his retirement in 1970 Richter founded, with other Caltech faculty, a consulting firm to advise on the seismic safety of engineering projects. His encounters with the press also made him a well-known debunker of unwarranted earthquake predictions.

During the 1950s Richter also wrote Elementary Seismology, which—despite its title—is a complete description of all aspects of the study of earthquakes, their causes, effects, and geography, as well as an outline of the development of seismology over time. The book reflects both Richter’s wide knowledge of the subject, and his preference for keeping inferences close to observations and avoiding undue speculation; it helped to train a generation of American seismologists. Richter’s primary professional affiliation was with the Seismological Society of America, of which he was president in 1959; in 1976 he received the Society’s Harry Fielding Reid Medal.

While a man of considerable charm and some humor, Richter was often awkward socially: he could be blunt, thin-skinned, and somewhat mercurial. He was devoted to his science, even installing a seismic recorder in his living room; but he also privately maintained wider interests, notably in botany, and wrote fiction and poetry, largely unpublished. He enjoyed the outdoors both alone and with his wife Lillian, whom he married in 1928, and who predeceased him in 1972; they had no children.

Though the magnitude scale was invented to solve a purely local problem, its use expanded far beyond that. As a description of earthquake size it began to be used in newspaper reports in the late 1940s, and has become well embedded in popular consciousness, along with the term

Richter scale. In seismology it also became a standard, or rather multiple standards, as different definitions were developed for different kinds of earthquakes; attempting to make these consistent with Richter’s original definition, determining the interrelations between different scales, and finding the reasons for the differences, have all been ongoing research activities.

BIBLIOGRAPHY

WORKS BY RICHTER

“An Instrumental Earthquake Magnitude Scale.” Bulletin of the Seismological Society of America 25 (1935): 1–32.

With Beno Gutenberg. “Richter Frequency of Earthquakes in California.” Bulletin of the Seismological Society of America 34 (1944): 185–188.

———. Seismicity of the Earth and Associated Phenomena, 2nd edition. Princeton, NJ: Princeton University Press, 1954. Elementary Seismology. San Francisco: W.H. Freeman, 1958.

OTHER SOURCES

Allen, Clarence. “Charles F. Richter: A Personal Tribute.” Bulletin of the Seismological Society of America 77 (1987): 2232–2233.

Geschwind, Carl-Henry. California Earthquakes: Science, Risk, and the Politics of Hazard Mitigation. Baltimore, MD: Johns Hopkins University Press, 2001.

Goodstein, Judith R. “Waves in the Earth: Seismology Comes to Southern California.” Historical Studies in the Physical and Biological Sciences 14 (1984): 201–230.

Hough, Susan Elizabeth. Richter’s Scale: Measure of an Earthquake, Measure of a Man. Princeton, NJ: Princeton University Press, 2007.

Duncan Carr Agnew