The effect of one earthquake ~ above the Earth"s surface is called the intensity. The strongness scale consists of a collection of certain key responses together as civilization awakening, motion of furniture, damage to chimneys, and finally - total destruction. Although numerousintensity scales have been occurred over the critical several century to advice the impacts of earthquakes, the one at this time used in the United claims is the amendment Mercalli (MM) strongness Scale. That was developed in 1931 by the American seismologists harry Wood and also Frank Neumann. This scale, written of raising levels of strongness that selection from imperceptible shaking to catastrophic destruction, is designated by roman inn numerals. It does not have actually a mathematics basis; instead it is an arbitrarily ranking based upon observed effects.

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The amendment Mercalli Intensity value assigned to a details site after ~ an earthquake has a more meaningful measure up of severity come the nonscientist 보다 the magnitude due to the fact that intensity describes the effects actually proficient at that place.

The lower numbers of the intensity scale generally attend to the path in i m sorry the earthquake is feeling by people. The higher numbers the the scale are based upon observed structure damage. Structural engineers usually add information for assigning intensity values of VIII or above.


Abridged from The Severity of one Earthquake, basic Interest publication 1989-288-913

History and also Details that MMI

The complying with is an excerpt from Intensity Distribution and Isoseismal Maps for the Northridge, California, Earthquake of January 17,1994.

The strongness of one earthquake in ~ a ar is a number that characterizes the severity of floor shaking in ~ that location by considering the effects ofthe shiver on people, top top manmade structures, and on the landscape.

Intensities assigned by the U. S. Geology Survey and also (prior come 1973) by organ in the U. S. Room of commerce have for plenty of decades been based upon the modification Mercalli Intensity scale of 1931 (Wood and Neumann, 1931), i m sorry we commonly refer to just as the "Modified Mercalli" or "MM" scale. The range lists criteria the permit the seismologist to represent the severity of soil shaking in a neighborhood or component of a community by a number. Suffer with the MM scale in the decades since 1931 has shown that part criteria are more reliable 보다 others as signs of the level of soil shaking. Moreover, building and construction methods have adjusted appreciably due to the fact that the scale was introduced. Assigning the MM strongness values because of this involves use of the initial criteria of Wood and Neumann (1931) with amendments and modifications that have been emerged in the decades since 1931.


The modified Mercalli range is given as originally abridged by Wood and also Neumann (1931) ... The unabridged scale is reproduced in Stover and Coffman (1993). ... Due to the fact that 1931 ithas become clear that countless phenomena that Wood and also Neumann (1931) originally used as criteria to define the greatest Modified Mercalli intensities (X and above) are related much less to the level of ground shaking 보다 to the existence of ground problems susceptible come spectacular fail or to the ease with which seismic faulting of various style and also depth have the right to propagate come the soil surface. Criteria based on such phenomena space downweighted now in assigning the intensities (Stover and also Coffman, 1993).

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Dewey, James, B. Glen Reagor, L. Dengler, K. Moley (1995). Intensity Distribution and also Isoseismal Maps for the Northridge, California, Earthquake of January 17,1994, Open-File Report 95-92.Stover, C. W., and Coffman, J. L. (1993). Seismicity that the united States, 1568-1989 (Revised): U. S. Geological inspection Professional file 1527, 418 p.Wood, H. O., and Neumann, open minded (1931). Amendment Mercalli Intensity scale of 1931: Seismological society of America Bulletin, v. 21, no. 4, p. 277-283.