How earthquakes are measured

(CNN)Earthquakes are measured using seismographs, which monitor the seismic waves that travel through the Earth after an earthquake strikes.

Scientists used the Richter Scale for many years but now largely follow the "moment magnitude scale," which the U.S. Geological Survey says is a more accurate measure of size.
Here are the magnitude classes:
Microearthquake:
    -- Magnitude: Less than 3.0
    -- Damage: Little to none
    Minor earthquake:
    -- Magnitude: 3.0 - 3.9
    -- Damage: Little to none
    Light earthquake:
    -- Magnitude: 4.0 - 4.9
    -- Damage: Moderate
    Moderate earthquake:
    -- Magnitude: 5.0 - 5.9
    -- Damage: Considerable
    Strong earthquake:
    -- Magnitude: 6.0 - 6.9
    -- Damage: Severe
    Major earthquake:
    -- Magnitude: 7.0 - 7.9
    -- Damage: Widespread, heavy
    Great earthquake:
    -- Magnitude: 8.0 and up
    -- Damage: Tremendous