Modified Mercalli Seismic Intensity Scale

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.