Question
How do I interpret magnitudes and magnitude types?
Answer
Earthquake Magnitude Descriptions
Magnitudes can be based on any of the following:
| Scale | Definition |
|---|---|
| Mw | estimates of the seismic moment |
| Mb | maximum amplitudes of teleseismic body waves |
| Ms | surface waves |
| Ml | local recordings |
| Md | signal duration |
Magnitude classes
| Class | Value range |
|---|---|
| Great | M > =8 |
| Major | 7 < =M < 7.9 |
| Strong | 6 < = M < 6.9 |
| Moderate | 5 < =M < 5.9 |
| Light | 4 < =M < 4.9 |
| Minor | 3 < =M < 3.9 |
| Micro | M < 3 |
More Information
The USGS website describes magnitude calculations here:
http://earthquake.usgs.gov/earthquakes/eventpage/terms.php
Here is another useful description of magnitude types and calculations:
http://www.weather.gov.hk/education/edu02rga/article/ele-EarthquakeMagnetude_e.htm
Updated: 05/18/2017
