Scientists rate the strength of earthquakes by their magnitude. It seems pretty obvious that the higher the magnitude, the more intense the earthquake. But you may wonder just how much worse a magnitude 6 earthquake is than a magnitude 4, or whether a magnitude 3 is even worth worrying about. Wonder no more. Here's how the earthquake magnitude scale works.
An earthquake's magnitude describes how much the ground moves. The scale is logarithmic, which means that when the magnitude increases by one (say from 3 to 4, or from 4 to 5) as the amount of ground motion increases by ten times. That is, a magnitude 3 quake leads to ten times as much ground motion as a magnitude 2 quake, and a magnitude 2 leads to ten times as much motion as a magnitude 1. Which means that a magnitude 3 is a hundred times as violent as a magnitude 1, and a hundred times less violent than a magnitude 5.
The magnitude scale also tells us just how much energy an earthquake released. For example, a magnitude 1 earthquake releases the same amount of energy as released when 30 pounds of TNT explodes. Although a magnitude 2 earthquake makes the ground move ten times as much as a magnitude 1, it releases 32 times as much energy -- or roughly as much as a ton of TNT. A magnitude 5 earthquake packs the punch of a moderate nuclear weapon, and a magnitude 12 quake would be enough to put a crack all the way through the center of the Earth.