The Modified Mercalli intensity scale
Revisions arising from New Zealand experience
Recent studies of the effects and Modified Mercalli (MM) intensities of New Zealand earthquakes have established criteria that will improve the reliability of intensities assigned using a number of effects, particularly the incidence of chimney damage and a wide range of environmental phenomena. The proportions of brittle chimneys which were damaged at intensities MM5–MM10 have been counted from the very detailed database of the 1968 Mw 7.2 Inangahua earthquake, and are shown to relate well to the proportions of chimneys which fell in 10 other earthquakes. Criteria based on environmental effects at intensities MM5-MM10 have been extended based on detailed studies of 22 earthquakes. These criteria have been adopted in an international intensity scale for environmental effects.
It was also found that the stopping of clocks should be a criterion for MM3, not MM5, and similarly the disturbance of liquids should be used at the threshold intensity of MM3 rather than MM4, as in the present MM intensity scale.
With the probable saturation of intensity at MM10, the criteria for MM12 have been omitted.
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