Modified Mercalli scale
The Mercalli intensity scale is a seismic scale used for measuring the intensity of an earthquake. It measures the effects of an earthquake. It is distinct from the moment magnitude (Mw) usually reported for an earthquake, which is a measure of the energy released (sometimes misreported as the Richter magnitude, ML). The intensity of an earthquake is not entirely determined by its magnitude. It is not based on first physical principles, but is, instead, empirically based on observed effects.
The Mercalli scale quantifies the effects of an earthquake on the Earth's surface, humans, objects of nature, and man-made structures on a scale from I (not felt) to XII (total destruction). Values depend upon the distance from the earthquake, with the highest intensities being around the epicentral area. Data gathered from people who have experienced the quake are used to determine an intensity value for their location. The Italian volcanologist Giuseppe Mercalli revised the widely used simple ten-degree Rossi–Forel scale between 1884 and 1906, creating the Mercalli Intensity scale which is still used nowadays.
In 1902, the ten-degree Mercalli scale was expanded to twelve degrees by Italian physicist Adolfo Cancani. It was later completely re-written by the German geophysicist August Heinrich Sieberg and became known as the Mercalli–Cancani–Sieberg (MCS) scale.
The Mercalli–Cancani–Sieberg scale was later modified by Harry O. Wood and Frank Neumann, and published in English in 1931 as the Mercalli–Wood–Neumann (MWN) scale. It was later improved by Charles Richter, the father of the Richter magnitude scale.
The scale is known today as the Modified Mercalli scale (MM) or Modified Mercalli Intensity scale (MMI).
The lower degrees of the Modified Mercalli Intensity scale generally deal with the manner in which the earthquake is felt by people. The higher numbers of the scale are based on observed structural damage.
This table gives Modified Mercalli scale intensities that are typically observed at locations near the epicenter of the earthquake.
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