Charles Francis Richter - Richter Scale

Richter Scale

At the time when Richter began a collaboration with Gutenberg, the only way to rate shocks was a scale developed in 1902 by the Italian priest and geologist Giuseppe Mercalli. The Mercalli scale classified earthquakes from 1 to 12, depending on how buildings and people responded to the tremor. A shock that set chandeliers swinging might rate as a 1 or 2 on this scale, while one that destroyed huge buildings and created panic in a crowded city might count as a 10. The obvious problem with the Mercalli scale was that it relied on subjective measures of how well a building had been constructed and how used to these sorts of crises the population was. The Mercalli scale also made it difficult to rate earthquakes that happened in remote, sparsely populated areas.

The scale developed by Richter and Gutenberg (which became known by Richter's name only) was instead an absolute measure of an earthquake's intensity. Richter used a seismograph – an instrument generally consisting of a constantly unwinding roll of paper, anchored to a fixed place, and a pendulum or magnet suspended with a marking device above the roll – to record actual earth motion during an earthquake. The scale takes into account the instrument's distance from the epicenter, or the point on the ground that is directly above the earthquake's origin. Richter chose to use the term "magnitude" to describe an earthquake's strength because of his early interest in astronomy; stargazers use the word to describe the brightness of stars. Gutenberg suggested that the scale be logarithmic, so that a quake of magnitude 7 would be ten times stronger than a 6, a hundred times stronger than a 5, and a thousand times stronger than a 4. (The 1989 Loma Prieta earthquake that shook San Francisco was magnitude 7.1.)

The Richter scale was published in 1935 and immediately became the standard measure of earthquake intensity. Richter did not seem concerned that Gutenberg's name was not included at first; but in later years, after Gutenberg was already dead, Richter began to insist that his colleague be recognized for expanding the scale to apply to earthquakes all over the globe, not just in southern California. Since 1935, several other magnitude scales have been developed. Depending on what data is available, different ones are used, but all are popularly known by Richter scale.