Earthquakes are measured using a system called the Richter System. This system uses numbers 1-11 to describe how much energy was released by the earthquake. There is also a less heard of Mercalli scale, which measures the amount of damage caused. So, it is possible to have a low Richter and a high Mercalli for the same earthquake.

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The richtor scale as stated before measures how much energy was released by the earthquake. Between two numbers on the richter scale, there is a 10x difference. For instance, if a variable for the damage caused by a earthquake of magnitude 5 (d) than the magnitude of a earthquake with a magnitude of 6 would be (10d)

Earthquakes with a magnitude of 1 to about 3 can not be felt by us, and they are only detected by instruments. There are more than 500,000 earthquakes like this every year.

Earthquakes with a magnitude of 3 to 4 are often felt, but there is no real damgae. Water may sway in glasses, but not much else will happen. There are about 50,000 of these every year.

Earthquakes with a magnitude of 5 are felt by most people, and there can be minor damage to buildings near the epicenter. There are about 500 of these every year.

Earthquakes with a magnitude of 6 may destroy poorly build buildings and/or cause damage within 10 miles of the epicenterThere are up to 200 of these every year.

Earthquakes with a magnitude of 7 are even stronger. These are considered "major" earthquakes, and cause a lot of damage to buildings up to 100 miles of the epicenter. There are up to 20 of these every year.

Earthquakes with a magnitude of 8 are extremely strong. These make buildings collapse, bridges collapse, railroads get wrecked. These actually include large loss of life. These cause severe damage within/for over 100 miles from the epicenter. There are up to 10 every year.

Earthquakes with a magnitude of 9 are rare giant earthquakes. These cause massive damage for over 1000 miles, and cause massive loss of life.

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The modifed mercalli scale measures the intensity of an earthquake. It was created in 1931 by Harry Wood and Frank Neumann. It is composed of 12 stages, each signified by a roman numeral. The lower numerals deal with how people feel the earthquake, when the higher numbers deal with the structural damage done to buildings. (VII or higher)

I. - These earthquaks are not really felt by anyone. The only time people feel these are when they are under very special conditions

II. - These are only felt by a few people. These people are usually in really high buildings, or are sleeping.

III. - These are usually felt by people inside, and people outside do not notice them at all.

IV. - These are felt inside by almost eveyone. People are sometimes awake from sleep, and it feels like a slight vibration.

V. - These are felt by almost everyone, almost everyone is awoken. Some things break, and some crack.

VI. - These are felt by everyone. Lots of people are scared by these quakes, and there is minor damage.

VII. - These cause a lot of damage in poorly consturcted builtings.

VIII. - These cause a lot of damage in normally built buildings.

IX. - These cause a lot of damage in specially build earthquake resistant buildings.

X. - These cause many wooden structures to get destroyed, most foundation layed buildings are destroied.

XI. - Few structures remain.

XII. - Total destruction. Everything thrown into air.

More information about how/why earthquakes occur can be found [here]

More information about what an earthquake is can be found [here]

Information about major past earthquakes can be found [here]

Earthquake links can be found [here]

More earthquake pictures can be found [here]