The Modified Mercalli Intensity Scale

Simplified, from reference.

In New Zealand, where earthquakes occur from near the surface right down to a depth of over 600 km, the Modified Mercalli intensity scale is a better indicator of an earthquake's effects on people and their environment.

New Zealand scientists have modified it further to suit New Zealand conditions. It is used by many professionals who need to know the relationship between the strength of shaking at ground level and the degree of damage.

Category Definition
MM 1: Imperceptible Barely sensed only by a very few people.
MM 2: Scarcely felt Felt only by a few people at rest in houses or on upper floors.
MM 3: Weak Felt indoors as a light vibration. Hanging objects may swing slightly.
MM 4: Largely observed Generally noticed indoors, but not outside, as a moderate vibration or jolt. Light sleepers may be awakened. Walls may creak, and glassware, crockery, doors or windows rattle.
MM 5: Strong Generally felt outside and by almost everyone indoors. Most sleepers are awakened and a few people alarmed. Small objects are shifted or overturned, and pictures knock against the wall. Some glassware and crockery may break, and loosely secured doors may swing open and shut.
MM 6: Slightly damaging Felt by all. People and animals are alarmed, and many run outside. Walking steadily is difficult. Furniture and appliances may move on smooth surfaces, and objects fall from walls and shelves. Glassware and crockery break. Slight non-structural damage to buildings may occur.
MM 7: Damaging General alarm. People experience difficulty standing. Furniture and appliances are shifted. Substantial damage to fragile or unsecured objects. A few weak buildings are damaged.
MM 8: Heavily damaging Alarm may approach panic. A few buildings are damaged and some weak buildings are destroyed.
MM 9: Destructive Some buildings are damaged and many weak buildings are destroyed.
MM 10: Very destructive Many buildings are damaged and most weak buildings are destroyed.
MM 11: Devastating Most buildings are damaged and many buildings are destroyed.
MM 12: Completely devastating All buildings are damaged and most buildings are destroyed.