Richter Scale
The Richter scale, used to measure earthquake intensity, was developed in 1953 by Charles Richter. IT measures an earthquake's magnitude (intensity) on a scale of 1 to 8.8 which means that each whole number on the scale represents a 10-fold increase in power.
Each magnitude number represents the maximum amplitude of a seismic wave at a distance of about 100 miles (161 kilometers). The difference in time between the first and second (primary and secondary) waves is measured, and another factor is added (which takes into account the fact that the waves become weaker as they travel away from the focus) to determine the magnitude of the earthquake.
| Richter Number | Increase in Magnitude | Richter Number | Approximate Energy Released (Amount of TNT) | |
| 1 | 1 | 1 | 170 grams | |
| 2 | 10 | 2 | 6 kilograms | |
| 3 | 100 | 3 | 179 kilograms | |
| 4 | 1,000 | 4 | 5 metric tons | |
| 5 | 10,000 | 5 | 179 metric tons | |
| 6 | 100,000 | 6 | 5,643 metric tons | |
| 7 | 1,000,000 | 7 | 179,100 metric tons | |
| 8 | 10,000,000 | 8 | 5,643,000 |
| Magnitude | Description | Average occurrence |
| 1.0 to 2.0 | Very Minor | 8,000 a day |
| 2.0 to 3.0 | Very Minor | 1,000 a day |
| 3.0 to 4.0 | Minor | 49,000 annually |
| 4.0 to 5.0 | Light | 6,200 annually |
| 5.0 to 6.0 | Moderate | 800 annually |
| 6.0 to 7.0 | Strong | 120 annually |
| 7.0 to 8.0 | Major | 18 annually |
| 8.0 and higher | Devastating | 1 annually |