modified Mercalli intensity scale

This is a scale designed to describe how an earthquake is felt by people (more at the lower end) or how much damage results from it (at the higher end).

I. Not felt
II. Very weak: felt only by a few people, mainly at upper floors of buildings
III. Weak: felt noticeably by people indoors, especially at upper floors of buildings; stationary motor vehicles might rock.
IV. Light: felt indoors by many, outdoors by few. Things like windows, doors and dishes might be disturbed; walls might make creaking noises. May wake some people up from sleep.
V. Moderate: felt by nearly everyone; many would be woken at night. Some dishes and windows are broken; objects are overturned.
VI. Strong: felt by all. Some heavy furniture is moved; there may be fallen plaster. Few instances of serious damage.
VII. Very strong: damage is minor in “well-designed” structures, slight to moderate in “well-built” structures, but may be extensive in “poorly-built” structures. Chimneys may break.
VIII. Severe: damage is slight in buildings designed to withstand earthquakes, but may be severe in those that are not. Heavy furniture overturned.
IX. Violent: considerable damage even to buildings designed to withstand earthquakes. Widespread destruction to structures that were not. Buildings are lifted off foundations; liquefaction occurs.
X. Extreme: some well-built wooden structures are destroyed; most masonry and frame-based structures are destroyed, including the foundations. Rails are bent.
XI. Extreme: few structures remain standing. Bridges are destroyed. Fissures erupt in the ground. Underground pipelines are rendered useless. Earth slumps in places. Rails are bent a lot.
XII. Extreme: damage is total; waves are seen travelling along the ground; lines of sound and sight are distorted. Objects are thrown up into the air.

There is a correlation between the MMI and the seismic magnitude, but it is not absolute. Factors like the depth of an earthquake below the ground can make a difference.