SHAKE, RATTLE & ROLL
One measure of magnitude is the Richter scale, which is a mathematical theory, not a piece of equipment. It expresses how much total shaking an earthquake produces. Each number in the scale represents an increase of 10 times over the number preceeding it. An earthquake of 7.0 is ten times bigger than an earthquake of 6.0 and 100 times bigger than an earthquake of 5.0. Although scientists now use newer, more acurate, and more complicated scales, earthquakes are still reported to the public using this older, simpler system.
Earthquakes of less than 3.0 are too small to feel, but are measured by scientific instruments. Between 3.0 and 5.0, people can feel an earthquake but damage to property and injuries to people usually aren't serious. Earthquakes above 5.0 cause damage and above 7.0, they are considered major.