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THE MERCALLI SCALE:
The social impact of earthquakes
The Modified Mercalli Scale, from USGS Circular 1045,
"Lessons Learned from the Loma Prieta, California,
Earthquake of October 17, 1989."
Edited by the Earth
Sciences & Map Library, 2/1/94.
I Not felt by people, except rarely under especially
II Felt indoors only by persons at rest, especially on
upper floors. Some hanging objects may swing.
III Felt indoors by several. Hanging objects may swing
slightly. Vibration like passing of light trucks.
Duration estimated. May not be recognized as an
IV Felt indoors by many, outdoors by few. Hanging
objects swing. Vibration like passing of heavy
trucks; or sensation of a jolt like a heavy ball
striking the walls. Standing automobiles rock.
Windows, dishes, doors rattle. Wooden walls and
frames may creak.
V Felt indoors and outdoors by nearly everyone;
direction estimated. Sleepers wakened. Liquids
disturbed, some spilled. Small unstable objects
displaced or upset; some dishes and glassware
broken. Doors swing; shutters, pictures move.
Pendulum clocks stop, start, change rate. Swaying
of tall trees and poles sometimes noticed.
VI Felt by all. Damage slight. Many frightened and
run outdoors. Persons walk unsteadily. Windows,
dishes, glassware broken. Knickknacks and books
fall off shelves; pictures off walls. Furniture
moved or overturned. Weak plaster and masonry
VII Difficult to stand. Damage negligible in buildings
of good design and construction; slight to moderate
in well-built ordinary buildings; considerable in
badly designed or poorly built buildings. Noticed
by drivers of automobiles. Hanging objects quiver.
Furniture broken. Weak chimneys broken. Damage to
masonry; fall of plaster, loose bricks, stones,
tiles, and unbraced parapets. Small slides and
caving in along sand or gravel banks. Large bells
VIII People frightened. Damage slight in specially
designed structures; considerable in ordinary
substantial buildings, partial collapse; great in
poorly built structures. Steering of automobiles
affected. Damage or partial collapse to some
masonry and stucco. Failure of some chimneys,
factory stacks, monuments, towers, elevated tanks.
Frame houses moved on foundations if not bolted
down; loose panel walls thrown out. Decayed
pilings broken off. Branches broken from trees.
Changes in flow or temperature of springs and
wells. Cracks in wet ground and on steep slopes.
IXGeneral panic. Damage considerable in specially
designed structures; great in substantial buildings
with some collapse. General damage to foundations;
frame structures, if not bolted, shifted off
foundations and thrown out of plumb. Serious
damage to reservoirs. Underground pipes broken.
Conspicuous cracks in ground; liquefaction.
X Most masonry and frame structures destroyed with
their foundations. Some well-built wooden
structures and bridges destroyed. Serious damage
to dams, dikes, embankments. Landslides on river
banks and steep slopes considerable. Water
splashed onto banks of canals, rivers, lakes.
Sand and mud shifted horizontally on beaches and
flat land. Rails bent slightly.
XI Few, if any masonry structures remain standing.
Bridges destroyed. Broad fissures in ground; earth
slumps and landslides widespread. Undergound
pipelines completely out of service. Rails bent
XII Damage nearly total. Waves seen on ground
surfaces. Large rock masses displaced. Lines of
sight and level distorted. Objects thrown upward
into the air.
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Document maintained on server by: Earth Sciences & Map Library
Last updated 3/9/1995.