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 Faint 1.0 to 2.0 Felt by very few people; barely noticeable.
II Faint 2.0 to 3.0 Felt by a few people, especially on upper floors.
III Weak 3.0 to 4.0 Noticeable indoors, especially on upperfloors, but may not be recognized as an earthquake.
IV Light 4.0 Felt by many indoors, few outdoors. May feel like heavy truck passing by.
V Moderate 4.0 to 5.0 Felt by almost everyone, some people awakened. Small objects moved. trees and poles may shake.
VI Strong 5.0 to 6.0 Felt by everyone. Difficult to stand. Some heavy furniture moved, some plaster falls. Chimneys may be slightly damaged.
VII Very Strong 6.0 Slight to moderate damage in well built, ordinary structures. Considerable damage to poorly built structures. Some walls may fall.
VIIISevere 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 Severe 7.0 Considerable damage to specially built structures, buildings shifted off foundations. Ground cracked noticeably. Wholesale destruction. Landslides.
X Severe 7.0 to 8.0 Most masonry and frame structures and their foundations destroyed. Ground badly cracked. Landslides. Wholesale destruction.
XI Severe 8.0 Total damage. Few, if any, structures standing. Bridges destroyed. Wide cracks in ground. Waves seen on ground.
XII Severe 8.0 or greater Total damage. Waves seen on ground. Objects thrown up into air.

Data for this comparison was copied from http://www.geo.mtu.edu/UPSeis/Mercalli.html
Data courtesy of GeoNet, Faultlines courtesy of GNS Science and NIWA emailFeedback © 21/11/2024 12:00:00 am Chris Crowe