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Magnitude vs. Intensity
Magnitude is the rating or size assigned to a given earthquake independent of the place of observation. HVO uses amplitude (height in millimeters of wave motion) and/or duration (length in seconds of wave motion) to calculate magnitude. Amplitude magnitude is determined using the Richter Scale. Duration magnitude is determined by scaling the length of a recorded signal in seconds to a magnitude value.
Intensity is the description of how strong an earthquake was felt at a given site. It is a measurement of damage to man-made structures or changes in the earth's surface caused by an earthquake. Unlike the magnitude, intensity ratings may vary from one site to another. The Modified Mercalli Intensity Scale is the rating used to describe the results of an earthquake. This description is a vital tool that scientists depend on to learn the relative effects of an earthquake within a given locality.
If you felt an earthquake and would like to report it, go to the Earthquake Felt Report Form. We encourage you to submit such reports, which help us determine the intensity of the earthquake.
Updated: August 3, 2006 (pnf)