Earthquake magnitude is measured using a logarithmic scale.
Earthquake magnitude is measured using a logarithmic scale. Each whole number increase in magnitude represents a 10x increase in measured amplitude (a 6.0 is 10x as bad as a 5.0).
| Magnitude | Earthquake Effects | World-Wide Occurrence |
|---|---|---|
| 2.5 or less | Usually not felt, but can be recorded by seismograph. | Millions per year |
| 2.5 to 4.9 | Often felt, but generally causes no damage. | 50,000+ per year |
| 5.0 to 5.9 | Felt by everyone. At most slight damage to well-designed buildings. Can cause major damage to poorly constructed buildings over small regions. | 350 per year |
| 6.0 to 6.9 | Can cause damage to poorly constructed buildings and other structures in areas up to about 100 kilometers across where people live. | 100-150 per year |
| 7.0 to 7.9 | Causes damage to most buildings, some to partially or completely collapse or receive severe damage. Well-designed structures are likely to receive damage. Felt across great distances with major damage mostly limited to 250 km from the epicenter. | 10-20 per year |
| 8.0 to 8.9 | Major damage to buildings, and structures likely to be destroyed. Will cause moderate to heavy damage to sturdy or earthquake-resistant buildings. Damaging in large areas. Felt in extremely large regions. | 1-2 per year |
| 9.0 + | Near total destruction - severe damage or collapse to all buildings. Heavy damage and shaking extend to distant locations. Permanent changes in ground topography. | 1-3 per century |
Notes:
