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Why do we need more than one earthquake magnitude scale?

The Richter magnitude scale (ML), described above is the best known magnitude scale. Charles Richter developed it in the 1930s for use on earthquakes in southern California, using high-frequency data from nearby or 'local' stations. It is also the scale used by BGS to describe UK earthquakes when using our network of 140 monitoring local stations. Other magnitude scales include body-wave magnitude (mb), and surface wave magnitude (Ms). One of these three scales is generally used, depending on the frequency range and type of signal. Values for the magnitude of a given event may, therefore, vary according to the monitoring agency and preferred scale used. Although moment magnitude (Mw) is considered the most reliable measure of earthquake size, especially for the largest events, it is more difficult to routinely calculate and requires analysis of the frequency spectra of the earthquake.

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