The Moment Magnitude scale is a way to measure the power of earthquakes. The higher the number, the bigger the earthquake. It is the energy of the earthquake at the moment it happens. Like the similar and older Richter scale, it is logarithmic, with a base of ten.
less than 3.5
This would be a very weak earthquake. People would not feel it, but it would be recorded by Geologists
Generally felt by people, but it rarely causes damage.
Will not cause damage to well-designed buildings, but can cause damage or destroy small or poorly-designed ones.
Can be destructive in areas up to about 100 kilometers across where people live.
Considered a "major earthquake" that causes a lot of damage.
8 or greater
Large and destructive earthquake that can destroy large cities.