Scientists measure the force of an earthquake in several ways. The Richter Scale and the Modified Mercalli Scale are the two methods most often used to gauge an earthquake's strength and magnitude.
The Richter Scale provides an estimate of an earthquake's magnitude through the use of a very precise instrument called a seismograph. It measures and records the seismic waves, or vibrations, created by the sudden release of energy caused when segments of the Earth's crust move. The scale ranges from 1 to 10, but it is logarithmic. This means for example, that a recording of 7 would show that movement of the earth was 10 times greater than a recording of 6. Earthquakes with a Richter value of 6 or more are considered major in magnitude. The 1954 earthquake that exposed the fault in front of you measured 7.3 on the Richter Scale. By comparison, the famous San Francisco earthquake of 1906 had a value of 8.3 on the scale.
The Modified Mercalli Scale expresses how intense an earthquake's effects are in a given location. The scale's values range from "I - Not felt except by a very few, favorably situated", to "XII - Damage total, lines of sight and level disturbed, objects thrown into the air". A value on this scale is assigned only after eyewitness reports and results of field investigations are studied and interpreted. The maximum intensity of the 1954 earthquake was X, the same as the 1964 quake in Alaska. The 1906 San Francisco earthquake measured XI on the scale.