Earthquakes are measured in the Richter magnitude scale, in which a number quantifies the amount of seismic energy released.
The magnitude is determined from the logarithm of the amplitude of waves recorded by seismographs.
The Richter scale is a base-10 logarithmic scale – meaning that each number has an amplitude 10 times stronger than the previous. The scale is not used to express damage.
The scale was developed by Charles Richter is 1935 at the California Institute of Technology to mathematically compare earthquakes.
Less than 2.0 (Micro) Microquake, not felt
2.0-2.9 (Minor) Not felt, but recorded
3.0-3.9 (Minor) Felt, but rarely causes damage
4.0-4.9 (Light) Shaking of indoor items, not significant damage
5.0-5.9 (Moderate) Can cause major damage to old buildings
6.0-6.9 (Strong) Destructive up to 160km in populated areas
7.0-7.9 (Major) Serious damage over large areas
8.0-8.9 (Great) Serious damage in areas hundreds of km across
9.0-9.9 (Great) Devastating in areas several thousand km across
10+ (epic) Never recorded
'Major' quakes occur at a rate of about 18 per year, 'strong' quakes are recorded up to 120 per year on average.
