The scientific term for measuring earthquakes is "seismology."

Magnitude is the amount of energy released by an earthquake. Earthquakes with a magnitude less than 3 are considered minor quakes; those with a magnitude greater than or equal to 3 and less than or equal to 5 are considered perceptible earthquakes; earthquakes with a magnitude greater than 5 but less than 6 are considered moderate-strong quakes; earthquakes with a magnitude equal to or greater than 6 are considered strong quakes, among which those with a magnitude greater than or equal to 8 are considered great earthquakes.