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The formula above made it much easier to estimate the energy-based magnitude M w , but it changed the fundamental nature of the scale into a moment magnitude scale. USGS seismologist Thomas C. Hanks noted that Kanamori's M w scale was very similar to a relationship between M L and M 0 that was reported by Thatcher & Hanks (1973)
The original "body-wave magnitude" – mB or m B (uppercase "B") – was developed by Gutenberg 1945c and Gutenberg & Richter 1956 [25] to overcome the distance and magnitude limitations of the M L scale inherent in the use of surface waves. mB is based on the P and S waves, measured over a longer period, and does not saturate until around M 8.
Several scales have been historically described as the "Richter scale", [citation needed] especially the local magnitude M L and the surface wave M s scale. In addition, the body wave magnitude, mb , and the moment magnitude, M w , abbreviated MMS, have been widely used for decades. A couple of new techniques to measure magnitude are in the ...
The parameter b (commonly referred to as the "b-value") is commonly close to 1.0 in seismically active regions. This means that for a given frequency of magnitude 4.0 or larger events there will be 10 times as many magnitude 3.0 or larger quakes and 100 times as many magnitude 2.0 or larger quakes.
Seismic moment is the basis of the moment magnitude scale introduced by Caltech's Thomas C. Hanks and Hiroo Kanamori, which is often used to compare the size of different earthquakes and is especially useful for comparing the sizes of large (great) earthquakes. The seismic moment is not restricted to earthquakes.
Magnitude scales measure the inherent force or strength of an earthquake – an event occurring at greater or lesser depth. (The "M w" scale is widely used.) The MM scale measures intensity of shaking, at any particular location, on the surface. It was developed from Giuseppe Mercalli's Mercalli intensity scale of 1902.
The successful development of the local-magnitude scale encouraged Gutenberg and Richter to develop magnitude scales based on teleseismic observations of earthquakes. Two scales were developed, one based on surface waves, M s {\displaystyle M_{s}} , and one on body waves, M b {\displaystyle M_{b}} .
An important parameter in the calculation of seismic hazard, maximum magnitude (expressed as Moment magnitude scale) is also one of the more contentious.The choice of the value can greatly influence the final outcome of the results, yet this is most likely a size of earthquake that has not yet occurred in the region under study.