Earthquake magnitude (M) describes the energy release (or size) of an earthquake.
There are many types of earthquake magnitude scales, with the vast majority based on recorded seismic waveforms (Bormann 2002). Magnitude scales are logarithmic, correct for distance from the earthquake, and are unbounded (the smallest earthquakes are less than zero, and the largest recorded event to date is the 1960 M9.5, Chile earthquake).
Some magnitude scales are based on measurements of shorter-period body waves (primary (P) or secondary (S)-waves), and some are based on longer-period surface waves. The original (and most famous) magnitude scale, the “Richter scale” was developed in the 1930s for California earthquakes (Richter 1935). The modern and most commonly used magnitude scale is moment magnitude , Mw (Hanks and Kanamori 1979). It is based on seismic moment (Mo) release, which directly relates to the fault rupture area and amount of slip.
- Bormann P (2002) Chapter 3: Magnitude of seismic events (Section 3.2). In: Bormann P (ed) New manual of seismological observatory practice (NMSOP), vol 1. GeoForschungs Zentrum, Potsdam, pp 16–49Google Scholar
- Richter CF (1935) An instrumental earthquake magnitude scale. Bull Seismol Soc Am. Seismological Society of America 25(1–2):1–32Google Scholar