Earthquake violence is measured on the Richter Scale, devised in 1935. The scale is a logarithmic one, meaning each whole number represents shaking that is 10 times as strong as the preceding number. Magnitude 7 is 100 times as powerful as Magnitude 5.Requires Adobe Acrobat.
According to the National Earthquake Information Center, maintained by the U.S. Geological Survey in Denver, the ratings are:
Magnitude 1.0 to Magnitude 3.0: "Not felt except by a very few under especially favorable conditions."
Magnitude 3.0 to 3.9: At the lower end of this spectrum, the quake is felt by only a few people, especially on upper floors of buildings.
At the higher end, felt "quite noticeably by persons indoors, especially on upper floors of buildings." Many do not recognize it as an earthquake, as the vibrations are similar to those of a passing truck. The quake may cause stopped vehicles to rock slightly.
Magnitude 4.0 to 4.9: At the lower end of this rating, many people indoors feel it. Outside, a few sense it. At night, some people are awakened. "Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably."
Toward the upper end, the earthquake is felt by nearly everyone. At night, many are awakened. "Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop."
Magnitude 5.0 to 5.9: Even at the lower end, this quake is felt by all. Many people are frightened. Some heavy furniture may move. Plaster may fall here and there. Damage is slight.
On the upper end, damage is negligible in buildings of good design and construction, but slight to moderate in well-built, ordinary structures. Poorly built or badly designed structures will have "considerable damage" and some chimneys will be broken.
Magnitude 6.0 to 6.9: Toward Magnitude 6, "damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures." Chimneys, factory smokestacks, columns, monuments and walls will collapse. Heavy furniture will be overturned.
At the upper end of this range, "Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations."
Magnitude 7.0 and higher: On the lower end, "Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent."
Somewhat higher than 7.0, few if any masonry structures remain standing. "Bridges destroyed. Rails bent greatly."
Above that, "damage total."