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Modified Mercalli Intensity Scale

The Modified Mercalli (MM) Scale is a scale of seismic intensity used to measure (or rate) the effects of an earthquake at the different sites where it was felt.

The scale is given in roman numerals from I to XII (1 to 12) with I being the lowest and XII being the highest.

MM I Not felt by humans, but birds and animals may be disturbed.
MM II Felt by a few persons at rest indoors, especially by those on upper floors.

Felt indoors, but not identified as an earthquake by everyone. Vibrations likened to the passing of light traffic. Hanging objects may swing slightly.

MM IV Generally noticed indoors, but not outside. Like the passing of heavy traffic, or the jolt of a heavy object falling or striking the building. Walls and frame of building creak. Doors and windows rattle. Glassware and crockery rattle. Liquids in open vessels may be slightly disturbed.
MM V Generally felt outside, and by almost everyone indoors. Most sleepers awakened. A few people frightened. Small unstable objects may be displaced or upset. Some glassware and crockery may be broken. Some windows crack. Hanging pictures move. Doors and shutters swing.
MM VI Felt by all. People and animals alarmed. Many run outside. Difficulty experienced in walking steadily. Slight damage to Masonry D. Some plaster cracks or falls. Isolated cases of chimney damage. Windows and crockery broken. Objects fall from shelves, and pictures from walls. Heavy furniture moves. Unstable furniture overturns.
MM VII Difficulty experienced in standing. Noticed by drivers of motorcars. Trees and bushes strongly shaken. Large bells ring. Masonry D cracked and damaged. A few instances of damage to Masonry C. Loose brickwork dislodged. Unbraced parapets and architectural ornaments may fall. Weak chimneys break. Domestic rainwater tanks burst.
MM VIII Alarm may approach panic. Steering of motorcars affected. Masonry C damaged, with partial collapse. Masonry B damaged in some cases. Chimneys, factory stacks brought down. Some brick veneers damaged. Unsecured frame houses may move. Landslips in roadside cuttings.
MM IX Panic. Masonry D destroyed. Masonry C heavily damaged, sometimes collapsing completely. Masonry B seriously damaged. Damage to foundations. Brick veneers fall and expose frames. Ground cracking occurs. Minor damage to paths and roadways. Underground pipes broken. Serious damage to reservoirs.
MM X Most masonry structures destroyed. Some well-built wooden buildings and bridges seriously damaged. Railway lines slightly bent. Roads and pavements badly cracked. Spectacular sand and mud fountains.
MM XI Wooden frame structures destroyed. Great damage to railway lines. Great damage to underground pipes.
MM XII Damage virtually total.

Masonry Key

Masonry A Earthquake resistant structures. Built to a code.
Masonry B Reinforced buildings of good workmanship and with sound mortar.
Masonry C Buildings of ordinary workmanship, with mortar of average quality.
Masonry D Poor workmanship, poor mortar, or constructed of weak materials like mud brick and rammed earth.