Richter Scale
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The Richter scale is a logarithmic measure of earthquake magnitude. It was developed by seismologist Charles F. Richter working with Beno Gutenberg in 1935, and was applied to earthquakes in southern California.
It measures the energy released by an earthquake at its source, not the damage to buildings or how people felt the shaking. Therefore, a single magnitude value produces varying effects depending on the depth of the source, the type of ground, and the population density of the affected area.
Calculation method
Richter based the scale on the maximum amplitude of the seismic wave as recorded on a Wood–Anderson instrument, adjusted for the distance between the measuring station and the earthquake source. The result is calculated as a base-ten logarithm. This means that an increase of one unit represents a tenfold increase in wave amplitude, while the energy released increases roughly thirty-onefold.
Limitations and alternatives
The original scale, now called local magnitude (ML), works reliably only when the earthquake is far from the station and when the magnitude is small. For large earthquakes it saturates—the recorded amplitude does not increase further—meaning that very different earthquakes can appear to have the same rating.
For this reason, modern scientific organizations, including earthquake monitoring agencies, generally use the moment magnitude scale (Mw), which is based on the total seismic moment released. However, the media and public discourse continue to use the name Richter for any magnitude figure.