After an earthquake, you’ll often hear a seismologist say something like “A moderate earthquake has occurred in the southcentral region of Alaska.” But what does that mean? While these terms sound general, they actually have a very specific meaning.

These terms are magnitude classes and they help to put earthquake magnitude into context. The classification starts with “minor” for magnitudes between 3.0 and 3.9, where earthquakes generally begin to be felt, and ends with “great” for magnitudes greater than 8.0, where significant damage is expected.