The Mercalli Intensity Scale is a semi-quantitative scale used to classify the intensity of an earthquake by examining its effects on people and structures at the Earth's surface. It was conceived by Italian volcanologist Giuseppe Mercalli in 1902, and was in general use before the Richter scale was developed by Charles Francis Richter and Beno Gutenberg in 1935. The form currently used in the United States is the Modified Mercalli (MM) Intensity Scale. It was developed in 1931 by the American seismologists Harry Wood and Frank Neumann .
The lower numbers of the intensity scale generally deal with the manner in which the earthquake is felt by people. The higher numbers of the scale are based on observed structural damage. Structural engineers usually contribute information for assigning intensity values of VIII or above.
- (I) - Not felt except by a very few under especially favourable conditions.
- (II) - Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing.
- (III) - Felt quite noticeably by persons indoors, especially on the upper floors of buildings. Many do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a truck. Duration estimated.
- (IV) - Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
- (V) - Felt by nearly everyone; many awakened. Some dishes and windows broken. Unstable objects overturned. Pendulum clocks may stop.
- (VI) - Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken... books off shelves... some heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight.
- (VII) - Difficult to stand... furniture broken..damage negligible in building of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken. Noticed by persons driving motor cars.
- (VIII) - Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture moved.
- (IX) - General panic... 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.
- (X) - Some well built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.
- (XI) - Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.
- (XII) - Damage total. Lines of sight and level distorted. Objects thrown into the air.
Information from The Severity of an earthquake pamphlet of the U.S. Geological Survey and the website of the U.S. National Earthquake Information Center http://neic.usgs.gov in Golden, Colorado.
- A brief history of earthquake intensity scales http://www.earthquakes.bgs.ac.uk/hazard/histint.htm
Geology, Geophysics, Japan Meteorological Agency seismic intensity scale, Moment magnitude scale, Plate tectonics
Last updated: 02-10-2005 21:30:15
Last updated: 05-03-2005 17:50:55