Seismic Intensity
Seismic intensity scales are used to measure the intensity of an earthquake. A seismic intensity scale measures the effects of an earthquake, and is distinct from earthquake magnitude scales, usually reported for an earthquake in the United States. Earthquake Magnitude scales can be thought of as a measure of the total energy released by the earthquake. The intensity of an earthquake varies by sites, and is not totally determined by its magnitude.
The seismic scale most commonly used in the United States is the Mercalli Intensity scale (MMI). MMI quantifies the effects of an earthquake on the Earth's surface, humans, objects of nature, and man-made structures. The USGS version of the MMI scale ranges from I (not felt) to X+ (very violent shaking). Values depend upon the distance to the earthquake, with the highest intensities often being around the epicentral area. Data gathered from people who have experienced the quake are used to determine an intensity value for their location.
