Frequently Answered Question

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