Earthquake Scales
Richter Magnitude, Moment Magnitude and Mercalli Intensity.
The intensity of an earthquake can be described by scales as
- Moment magnitude (MW)
- Mercalli intensity
- Richter magnitude (ML)
Be aware when using the table below that the Mercalli scale is a measure of the local shaking and the Richter scale is a measure of the total energy in the whole earthquake and that the scales are not directly convertible.
| Mercalli Intensity | Richer Magnitude | Moment Magnitude | Actual Observation of the Earthquake | |
|---|---|---|---|---|
| Instrumental | I | 2 | 1.0 - 3.0 | Micro earthquakes, usually not felt - detected by instruments |
| Feeble | II | 2 | 3.9 | Often felt, especially on upper floors - detected by instruments |
| Slight | III | 3 | 4.0 | Felt noticeably indoors, vibration like passing vehicles, cars may rock |
| Moderate | IV | 4.9 | Felt indoors by many, felt outdoors by few. Dishes and doors disturbed, like a heavy truck nearby, walls-cracking sound | |
| Rather Strong | V | 4 | 5.0 | Felt by most people, slight damage. Some dishes and windows broken, some cracked plaster, trees disturbed |
| Strong | VI | 5 | 5.9 | Felt by all, many frightened and run outdoors. Damage minor to moderate |
| Very Strong | VII | 5 - 6 | 6.0 | Everyone runs outdoors. Much damage to poor designed buildings, some chimneys broken, noticed by people driving cars |
| Destructive | VIII | 6 | 6.9 | Everyone runs outdoors. Damage moderate to major. Minor damage to well designed structures, major damage in poor designed structures. Chimneys, columns and walls falls. Heavy furniture turned. Well water changes, sand and mud ejected |
| Ruinous | IX | 7 | 7.0 | Can cause serious damage over larger areas. Major damage in all structures, ground cracked, pipes broken, shift foundation |
| Disastrous | X | 7 - 8 | Major damage, most masonry and frame structures destroyed. Ground badly cracked, landslides, water sloshed over river banks, rails bent | |
| Very Disastrous | XI | 8 | Almost all masonry structures destroyed, bridges fall, big fissures in ground, land slumps, rails bent greatly | |
| Catastrophic | XII | >8 | Devastating in areas several thousand miles across. Total destruction, Ground surface waves seen, objects thrown in the air. All constructions destroyed. |
- Mercalli Intensity - based on actual observations of the damage - can not be measured on instruments
- Moment Magnitude - based on energy released - logarithmic scale
- Richter Magnitude - based on the movement of a needle - logarithmic scale
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