Richter magnitude scale Richter correlation tables based on Richter standard seismic event (formula_26, formula_27, formula_28). Below, formula_29 is the epicentral distance (in kilometers unless otherwise specified). The Lillie empirical formula: Where formula_31 is the amplitude (maximum ground displacement) of the P-wave, in micrometers, measured at 0.8 Hz. For distances formula_32 less than 200 km, and for distances between 200 km and 600 km, where formula_31 is seismograph signal amplitude in mm and formula_32 is in km. The Bisztricsany (1958) empirical formula for epicentral distances between 4˚ to 160˚: Where formula_38 is the duration of the surface wave in seconds, and formula_39 is in
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