Specral magnitudes and seismograms measure radiation from seismic sources

For over 100 years, efforts have been made to measure the strength of earthquakes. In 1935, Richter established the local magnitude scale, ML, for earthquakes in Southern California using Wood Anderson Seismographs. The seismic waves used had periods ranging from 0.1 s to 2 s. In 1945, Gutenberg [1945a] developed the surface wave magnitude scale (Ms) based on the amplitudes of horizontal surface waves with periods of (20±3) s, recorded at large distances. Gutenberg [1945b] also used seismic body P and S waves, with average periods of 5 s and 10 s, respectively, to introduce the bodywave magnitude scale (mb).