The Mercalli Intensity Scale provides a way to measure earthquakes not by scientific instruments alone, but by the effects felt by people and damage observed in the built environment. Unlike magnitude scales (which measure energy released), the Mercalli scale ranks an earthquake’s intensity on a Roman numeral scale from I (not felt) to XII (total destruction).
Levels of the Mercalli Intensity Scale:
I.
Not felt, except by a very few, under especially favorable circumstances.
II.
Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing.
III.
Felt quite noticeably indoors, especially on upper floors of buildings, but many people do not recognize it as an earthquake. Standing automobiles may rock slightly. Vibrations like a passing truck.
IV.
During the day, felt indoors by many, outdoors by few. At night, some awakened. Dishes, windows, doors disturbed; cracking sounds from walls. Sensation like heavy truck striking building. Standing automobiles rock noticeably.
V.
Felt by nearly everyone; many awakened. Some dishes, windows, etc. broken; a few instances of cracked plaster; unstable objects overturned. Disturbance of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop.
VI.
Felt by all; many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster or damaged chimneys. Structural damage slight.
VII.
Everybody runs outdoors. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable in poorly-built or badly designed structures; some chimneys broken. Noticed by people driving.
VIII.
Damage slight in specially-engineered structures; considerable in ordinary structures. Many buildings with partial collapse. Panel walls thrown out of some frame structures. Fall of chimneys, factory stacks, columns, monuments, masonry walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water.
IX.
Damage considerable in all structures. Well-designed frame structures thrown out of plumb; partial collapse in many substantial buildings. Buildings shifted off foundations. Ground conspicuously cracked. Underground pipes broken.
X.
Some well-built wooden structures destroyed; most masonry and frame structures destroyed, including foundations. Ground badly cracked. Rails bent. Landslides considerable on river banks and other steep slopes. Shifted sand and mud.
XI.
Few, if any, masonry structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipelines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly.
XII.
Damage total. Waves seen on ground surface. Lines of sight distorted. Objects thrown upward into the air.
Conclusion:
The Mercalli Intensity Scale is a powerful tool for understanding how earthquakes affect people, places, and structures. While it doesn’t measure energy, it captures something equally important human experience.
