The Richter scale measures the magnitude, or size, of an earthquake by using a seismograph to measure the ground motion an earthquake produces.
The scale is logarithmic. A measurement of 7 means an earthquake that has 10 times the ground motion of an earthquake that measures 6.
We can’t feel an earthquake that has a magnitude of less than 2.
Magnitude 5 earthquakes begin to cause real damage. The scale has no top number.
Another way to measure earthquakes is the modified Mercalli scale, which measures the intensity of an earthquake based on observations of the physical damage done.
It uses Roman numerals I through XII, in which I means no damage, VI means slight damage, and XII means total damage, with no structures left standing and objects thrown into the air.
A third way to measure earthquakes is the moment magnitude scale, which uses a seismogram to measure the movement of the Earth’s surface during the quake.