Richter magnitude scale reported by the press as Richter values, even for earthquakes of magnitude over 8, when the Richter scale becomes meaningless. Anything above 5 is classified as a risk by the USGS. The Richter and MMS scales measure the energy released by an earthquake; another scale, the Mercalli intensity scale, classifies earthquakes by their "effects", from detectable by instruments but not noticeable, to catastrophic. The energy and effects are not necessarily strongly correlated; a shallow earthquake in a populated area with soil of certain types can be far more intense in effects than a much more energetic deep earthquake in an
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