Richter magnitude scale from it empirically as a quantity without units, just a number designed to conform to the formula_3 scale. A spectral analysis is required to obtain formula_12, whereas the other magnitudes are derived from a simple measurement of the amplitude of a specifically defined wave. All scales, except formula_5, saturate for large earthquakes, meaning they are based on the amplitudes of waves which have a wavelength shorter than the rupture length of the earthquakes. These short waves (high frequency waves) are too short a yardstick to measure the extent of the event. The resulting effective upper limit of measurement for formula_17
Seismic magnitude scales well" with the seismic moment magnitude in the range of 4.5 to 7.5, but underestimate larger magnitudes. Body-waves consist of P-waves that are the first to arrive (see seismogram), or S-waves, or reflections of either. Body-waves travel through rock directly. The original "body-wave magnitude" – mB or m (uppercase "B") – was developed by and to overcome the distance and magnitude limitations of the scale inherent in the use of surface waves. is based on the P- and S-waves, measured over a longer period, and does not saturate until around M 8. However, it is not sensitive to events smaller