Measuring an Earthquake Earthquakes are measured in two different ways. Magnitude is calculated by seismologists from size of seismograph tracings. The Richter scale is most useful to scientists who compare the power of earthquakes. However, earthquake magnitude is less useful to disaster planners and citizens in a high risk earthquake area. This is because the damage due to shaking depends on the distance from the epicenter, local rock types, and a number of other factors.
Intensity is a more useful measure of earthquake shaking in any one location.
It is represented by the modified Mercalli scale. On the Mercalli scale, a value of I is the least intense motion and XII is the greatest ground shaking. Unlike magnitude, intensity can vary from place to place. In addition, intensity is not measured by machines, but by the reactions of people and structures to the violent motions during an earthquake. Intensity is more useful to planners and communities because it helps people to predict the violence of shaking in their area.