Charles Francis Richter in southern California. Since 1935, several other magnitude scales have been developed. Richter was an active and avowed naturist. He travelled to many nudist communities with his wife. At his retirement party, a group of colleagues at Caltech, called the "Quidnuncs," played and sang a ditty titled "Richter Scale," which gave examples of earthquakes in American history, told in ballad style. Richter was not amused, however; he was furious. The author of the song, Kent Clark, stated in a 1989 interview that Richter enjoyed the song. The song is played on the Dr. Demento show occasionally. Richter died of congestive
Moment magnitude scale band. To simplify this calculation, he noted that the lowest frequency parts of the spectrum can often be used to estimate the rest of the spectrum. The lowest frequency asymptote of a seismic spectrum is characterized by the seismic moment, . Using an approximate relation between radiated energy and seismic moment (which assumes stress drop is complete and ignores fracture energy), (where E is in Joules and is in Nformula_4m), Kanamori approximated by The formula above made it much easier to estimate the energy-based magnitude , but it changed the fundamental nature of the scale into a moment magnitude scale.