Editing Modified Mercalli intensity scale (section)

==History==
Italian volcanologist [[Giuseppe Mercalli]] formulated his first intensity scale in 1883.<ref>{{Harvnb|Davison|1921|p=103}}.</ref> It had six degrees or categories, has been described as "merely an adaptation" of the then-standard [[Rossi–Forel scale]] of 10 degrees, and is now "more or less forgotten".<ref>{{Harvnb|Musson|Grünthal|Stucchi|2010|p=414}}.</ref> Mercalli's second scale, published in 1902, was also an adaptation of the Rossi–Forel scale, retaining the 10 degrees and expanding the descriptions of each degree.<ref>{{Harvnb|Davison|1921|p=108}}.</ref> This version "found favour with the users", and was adopted by the Italian Central Office of Meteorology and Geodynamics.<ref>{{Harvnb|Musson|Grünthal|Stucchi|2010|p=415}}.</ref>

In 1904, Adolfo Cancani proposed adding two additional degrees for very strong earthquakes, "catastrophe" and "enormous catastrophe", thus creating a 12-degree scale.<ref>{{Harvnb|Davison|1921|p=112}}.</ref> His descriptions being deficient, [[August Heinrich Sieberg]] augmented them during 1912 and 1923, and indicated a [[peak ground acceleration]] for each degree.<ref>{{Harvnb|Davison|1921|p=114}}.</ref><ref name="Musson 2010 416"/> This became known as the "Mercalli–Cancani scale, formulated by Sieberg", or the "Mercalli–Cancani–Sieberg scale", or simply "MCS",<ref name="Musson 2010 416">{{Harvnb|Musson|Grünthal|Stucchi|2010|p=416}}.</ref> and was used extensively in Europe and remains in use in Italy by the [[National Institute of Geophysics and Volcanology]] (INGV).<ref name="INGV_intensity">{{Cite web |last=National Institute of Geophysics and Volcanology |title=Intensity evaluation method |url=http://legacy.ingv.it/roma/SITOINGLESE/activities/pererischio/macrosismica/macros/metod_val.html |access-date=2022-10-20 |archive-date=2022-10-20 |archive-url=https://web.archive.org/web/20221020112435/http://legacy.ingv.it/roma/SITOINGLESE/activities/pererischio/macrosismica/macros/metod_val.html |url-status=dead }}</ref>

When [[Harry O. Wood]] and Frank Neumann translated this into English in 1931 (along with modification and condensation of the descriptions, and removal of the acceleration criteria), they named it the "modified Mercalli intensity scale of 1931" (MM31).<ref>{{Harvnb|Wood|Neumann|1931}}.</ref> Some seismologists refer to this version as the "Wood–Neumann scale".<ref name="Musson 2010 416"/> Wood and Neumann also had an abridged version, with fewer criteria for assessing the degree of intensity.

The Wood–Neumann scale was revised in 1956 by [[Charles Francis Richter]] and published in his influential textbook ''Elementary Seismology''.<ref>{{Harvnb|Richter|1958}}; {{Harvnb|Musson|Grünthal|Stucchi|2010|p=416}}.</ref> Not wanting to have this intensity scale confused with the [[Richter scale]] he had developed, he proposed calling it the "modified Mercalli scale of 1956" (MM56).<ref name="Musson 2010 416"/>

In their 1993 compendium of historical seismicity in the United States,<ref>{{Harvnb|Stover|Coffman|1993}}</ref> Carl Stover and Jerry Coffman ignored Richter's revision, and assigned intensities according to their slightly modified interpretation of Wood and Neumann's 1931 scale,{{efn|Their modifications were mainly to degrees IV and V, with VI contingent on reports of damage to man-made structures, and VII considering only "damage to buildings or other man-made structures". See details at {{Harvnb|Stover|Coffman|1993|pp=3–4}}.}} effectively creating a new, but largely undocumented version of the scale.<ref>{{Harvnb|Grünthal|2011|p=238}}.  The most definitive exposition of the Stover and Coffman's effective scale is at {{Harvnb|Musson|Cecić|2012|loc=§12.2.2}}.</ref>

The basis by which the [[United States Geological Survey]] (and other agencies) assigns intensities is nominally Wood and Neumann's MM31. However, this is generally interpreted with the modifications summarized by Stover and Coffman because in the decades since 1931, "some criteria are more reliable than others as indicators of the level of ground shaking".<ref name="Dewey 1995 5">{{Harvnb|Dewey|Reagor|Dengler|Moley|1995|p=5}}.</ref> Also, construction codes and methods have evolved, making much of built environment stronger; these make a given intensity of ground shaking seem weaker.<ref>{{Harvnb|Davenport|Dowrick|2002}}.</ref> Also, some of the original criteria of the most intense degrees (X and above), such as bent rails, ground fissures, landslides, etc., are "related less to the level of ground shaking than to the presence of ground conditions susceptible to spectacular failure".<ref name="Dewey 1995 5"/>

The categories "catastrophe" and "enormous catastrophe" added by Cancani (XI and XII) are used so infrequently that current USGS practice is to merge them into a single category "Extreme" abbreviated as "X+".<ref>{{Harvnb|Musson|Grünthal|Stucchi|2010|p=423}}.</ref>