The Moment Magnitude Scale
The moment magnitude scale is based on the total amount of pressure released by the earthquake. This can be seen by the distance a fault moved and the force that was required to move it. The amount of pressure is estimated from the model recordings of other earthquakes at multiple stations around the world
For each number you go up on the magnitude scale, the amplitude of the earthquake recorded by a seismograph goes up ten times. For example: a magnitude 5 earthquake would result in ten times the level of ground shaking as a magnitude 4 earthquake.
A magnitude 1 earthquake releases as much energy as blowing up 170 grams of TNT. A magnitude 8 earthquake releases as much energy as detonating 6 million tons of TNT. Fortunately, most of the earthquakes that occur each year are magnitude 2.5 or less, too small to be felt by most people.