Intensities portray the effects of an earthquake in a particular location. These effects include potential damage, perception of shaking and permanent changes in topography. The most popular intensity scale used in the United States is the Modified Mercalli Scale (MMI) first developed in 1931.
MODIFIED MERCALLI INTENSITY SCALE
| |
MMI Value
| Full Description
|
I
| People do not feel any earth movement.
|
II
| Felt by persons at rest, on upper floors of tall buildings
|
III
| Felt by people indoors. Hanging objects swing back and forth.
Vibration from the earthquake may seem like the passing of light
trucks. May not be recognized as an earthquake.
|
IV
| Hanging objects swing. Vibration may seem like the passing
of heavy trucks or a jolt, like a heavy ball striking the walls.
Parked vehicles may rock noticeably. Windows, dishes, doors
may rattle and glasses clink. In the upper range of IV, walls of
wood frame buildings may creak.
|
V
| Almost everyone feels movement whether inside or outdoors.
Sleeping people are awakened. Liquids in containers are
disturbed; some are spilled. Small unstable objects are
displaced or overturned. Doors swing, close, or open.
Shutters, pictures on the wall move.
|
VI
| Almost everyone feels movement whether inside or outdoors.
Sleeping people are awakened. Liquids in containers are
disturbed; some are spilled. Small unstable objects are
displaced or overturned. Doors swing, close, or open.
Shutters, pictures on the wall move.
|
VII
| People have difficulty standing. Drivers on the road feel
their cars shaking. Furniture may be overturned and broken.
Loose bricks fall from buildings and masonry walls and cracks
in plaster and masonry may appear. Weak chimneys may
break at the roofline. Damage is slight to moderate in well-
built structures; considerable in poorly constructed buildings
and facilities.
|
VIII
| Drivers have trouble steering. Tall structures such as towers,
monuments and chimneys may twist and fall. Wood frame
houses that are not bolted to their foundations may shift and
sustain serious damage. Damage is slight to moderate in
well-constructed buildings,considerable in poorly constructed
buildings. Branches are broken and fall from trees. Changes
occur in flow or temperature of springs and wells. Cracks
appear in wet ground and on steep slopes.
|
IX
| Masonry structures and poorly constructed buildings suffer
serious damage or collapse. Frame structures, if not bolted,
shift off foundations. Serious damage to reservoirs.
Underground pipes broken. Conspicuous cracks in the
ground. In alluvial areas, sand and mud ejected and sand
craters are formed.
|
X
| Most masonry and frame structures destroyed along with
their foundations. Some well-built wooden structures and
bridges are destroyed. Serious damage to dams, dikes,
and embankments. Large landslides occur. Water thrown
on the banks of canals, rivers and lakes. Sand and mud
shift horizontally on beaches and flat land. Rails bent.
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