Moment magnitude scale as (in Joules). Unfortunately, the duration of many very large earthquakes was longer than 20 seconds, the period of the surface waves used in the measurement of . This meant that giant earthquakes such as the 1960 Chilean earthquake (M 9.5) were only assigned an . Caltech seismologist Hiroo Kanamori recognized this deficiency and he took the simple but important step of defining a magnitude based on estimates of radiated energy, , where the "w" stood for work (energy): Kanamori recognized that measurement of radiated energy is technically difficult since it involves integration of wave energy over the entire frequency
Order of magnitude An order-of-magnitude difference between two values is a factor of 10. For example, the mass of the planet Saturn is 95 times that of Earth, so Saturn is "two orders of magnitude" more massive than Earth. Order-of-magnitude differences are called decades when measured on a logarithmic scale. Other orders of magnitude may be calculated using bases other than 10. The ancient Greeks ranked the nighttime brightness of celestial bodies by 6 levels in which each level was the fifth root of one hundred (about 2.512) as bright as the nearest weaker level of brightness, and thus the brightest level being