Intensity scale
Water
An arbitrary scale to describe the degree of shaking at a particular place. The scale is not based on measurement, but on assessment by an experienced observer. A numerical index describing the effects of an earthquake on mankind, on structures built by mankind, and on the earth's surface. The scale in common use in the U. S. today is the Modified Mercalli Scale of 1931 with grades indicated by Roman numerals from I to XII. For more information, visit the U.S. Geological Survey National Earthquake Information Center.