Mercalli Scale
The size of an earthquake is often described using magnitude, which is the amount of energy released during an earthquake. However, not all of the energy released in an earthquake will necessarily be felt at the surface, depending on the earthquake's depth.

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.

For more details on this scale see http://en.wikipedia.org/wiki/Mercalli_intensity_scale and http://earthquake.usgs.gov/learn/topics/mercalli.php

Mercalli Intensity Richter Magnitude Witness Observations
I Instrumental 1.0 to 2.0 Generally not felt by people unless in favorable conditions.
II Weak 2.0 to 3.0 Felt only by a couple people that are sensitive, especially on the upper floors of buildings. Delicately suspended objects (including chandeliers) may swing slightly.
III Slight 3.0 to 4.0 Felt quite noticeably by people indoors, especially on the upper floors of buildings. Many do not recognize it as an earthquake. Standing automobiles may rock slightly. Vibration similar to the passing of a truck. Duration can be estimated. Indoor objects (including chandeliers) may shake.
IV Moderate 4.0 Felt indoors by many to all people, and outdoors by few people. Some awakened. Dishes, windows, and doors disturbed, and walls make cracking sounds. Chandeliers and indoor objects shake noticeably. The sensation is more like a heavy truck striking building. Standing automobiles rock noticeably. Dishes and windows rattle alarmingly. Damage none.
V Rather Strong 4.0 to 5.0 Felt inside by most or all, and outside. Dishes and windows may break and bells will ring. Vibrations are more like a large train passing close to a house. Possible slight damage to buildings. Liquids may spill out of glasses or open containers. None to a few people are frightened and run outdoors.
VI Strong 5.0 to 6.0 Felt by everyone, outside or inside; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken; books fall off shelves; some heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight to moderate to poorly designed buildings, all others receive none to slight damage.
VII Very Strong 6.0 Difficult to stand. Furniture broken. Damage light in building of good design and construction; slight to moderate in ordinarily built structures; considerable damage in poorly built or badly designed structures; some chimneys broken or heavily damaged. Noticed by people driving automobiles.
VIII Destructive 6.0 to 7.0 Little damage in specially built structures. Considerable damage to ordinary buildings, severe damage to poorly built structures. Some walls collapse.
IX Violent 7.0 General panic. Damage slight to moderate (possibly heavy) in well-designed structures. Well-designed structures thrown out of plumb. Damage moderate to great in substantial buildings, with a possible partial collapse. Some buildings may be shifted off foundations. Walls can fall down or collapse.
X Intense 7.0 to 8.0 Many well-built structures destroyed, collapsed, or moderately to severely damaged. Most other structures destroyed, possibly shifted off foundation. Large landslides.
XI Extreme 8.0 Few, if any structures remain standing. Numerous landslides, cracks and deformation of the ground.
XII Catastrophic 8.0 or greater Total destruction – everything is destroyed. Lines of sight and level distorted. Objects thrown into the air. The ground moves in waves or ripples. Large amounts of rock move position. Landscape altered, or leveled by several meters. Even the routes of rivers can be changed.
Data courtesy of GeoNet, Faultlines courtesy of GNS Science and NIWA emailFeedback © 2024 Chris Crowe