Moment magnitude scale both scales. Unlike other scales, the moment magnitude scale does not saturate at the upper end; there is no upper limit to the possible measurable magnitudes. However, this has the side-effect that the scales diverge for smaller earthquakes. Various ways of determining moment magnitude have been developed, and several subtypes of the scale can be used to indicate the basis used. Moment magnitude scale The moment magnitude scale (MMS; denoted as M" or M") is one of many seismic magnitude scales used to measure the size of earthquakes. The scale was developed in the 1970s to succeed the 1930s-era Richter
Richter magnitude scale used by astronomers. Second, he wanted a magnitude of zero to be around the limit of human perceptibility. Third, he specified the Wood-Anderson seismograph as the standard instrument for producing seismograms. Magnitude was then defined as "the logarithm of the maximum trace amplitude, expressed in microns", measured at a distance of 100 km. The scale was calibrated by defining a magnitude 3 shock as one that produces (at a distance of 100 km) a maximum amplitude of 1 micron (1 µm, or 0.001 millimeters) on a seismogram recorded by a Wood-Anderson torsion seismograph. Finally, Richter calculated a table of distance