Modified Mercalli Scale
|Magnitude and Intensity measure different
characteristics of earthquakes. Magnitude measures the energy released at
the source of the earthquake. Magnitude is determined from measurements on
seismographs. Intensity measures the strength of shaking produced by the
earthquake at a certain location. Intensity is determined from effects on
people, human structures, and the natural environment.
The following table gives intensities that are typically observed at locations near the epicenter of earthquakes of different magnitudes.
|Richter Scale Magnitude||Modified Mercalli Intensity|
|1.0 - 3.0||I||I. Not felt except by a very few under especially favorable conditions.|
|3.0 - 3.9||II - III||II. Felt only by a few persons at
rest, especially on upper floors of buildings.
III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.
|4.0 - 4.9||IV - V||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, windows broken. Unstable objects overturned. Pendulum clocks may stop.
|5.0 - 5.9||VI - VII||VI. Felt by all, many frightened.
Some heavy furniture moved; a few instances of fallen plaster. Damage
VII. Damage negligible in buildings 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.
|6.0 - 6.9||VII - IX||VIII. Damage slight in specially
designed structures; considerable damage in ordinary substantial buildings
with partial collapse. Damage great in poorly built structures. Fall of
chimneys, factory stacks, columns, monuments, walls. Heavy furniture
IX. 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.
XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.
XII. Damage total. Lines of sight and level are distorted. Objects thrown into the air.