What is considered a big earthquake? Earthquakes are also classified in categories ranging from minor to great, depending on their magnitude.
| Class | Magnitude |
| Great | 8 or more |
| Major | 7 – 7.9 |
| Strong | 6 – 6.9 |
| Moderate | 5 – 5.9 |
| Light | 4 – 4.9 |
| Minor | 3 -3.9 |
Earthquake Magnitude Scale
| Magnitude | Earthquake Effects | Estimated Number Each Year |
| 2.5 or less | Usually not felt, but can be recorded by seismograph. | 900,000 |
| 2.5 to 5.4 | Often felt, but only causes minor damage. | 30,000 |
| 5.5 to 6.0 | Slight damage to buildings and other structures. | 500 |
| 6.1 to 6.9 | May cause a lot of damage in very populated areas. | 100 |
| 7.0 to 7.9 | Major earthquake. Serious damage. | 20 |
| 8.0 or greater | Great earthquake. Can totally destroy communities near the epicenter. | One every 5 to 10 years |
