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Browse the 1966 Encyclopaedia of New Zealand
Graphic: An Encyclopaedia of New Zealand 1966.


This information was published in 1966 in An Encyclopaedia of New Zealand, edited by A. H. McLintock. It has not been corrected and will not be updated.

Up-to-date information can be found elsewhere in Te Ara.



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Modified Mercalli (MM) Intensity Scale

  1. Not felt except by a very few under especially favourable circumstances.

  2. Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing.

  3. Felt quite noticeably indoors, especially on upper floors of buildings, but many people do not recognise it as an earthquake. Standing motorcars may rock slightly. Vibration like passing of truck. Duration estimated.

  4. During the day felt indoors by many, outdoors by few. At night some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motorcars rock noticeably.

  5. Felt by nearly everyone; many awakened. Some dishes, windows, etc., broken; a few instances of cracked plaster; unstable objects overturned. Disturbance of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop.

  6. Felt by all; many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster or damaged chimneys. Damage slight.

  7. Everybody runs outdoors. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable in poorly built or badly designed structures; some chimneys broken. Noticed by persons driving motorcars.

  8. Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse; great in poorly built structures. Panel walls thrown out of frame structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water. Disturbs persons driving motorcars.

  9. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb; great in substantial buildings, with partial collapse. Buildings shifted off foundations. Ground cracked conspicuously. Underground pipes broken.

  10. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides considerable from river banks and steep slopes. Shifts sand and mud. Water splashed (slopped) over banks.

  11. Few, if any (masonry), structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipelines completely out of service. Earth slumps and landslips in soft ground. Rails bent greatly.

  12. Damage total. Waves seen on ground surfaces. Lines of sight and level distorted. Objects thrown upward into the air.

In New Zealand about 100 earthquakes are reported felt in an average year. On the more important occasions — usually several times a year — a questionnaire is issued to a large number of voluntary observers, and the information so obtained is used to draw an isoseismal map, showing contours of equally felt intensity. Diag. 1 shows an isoseismal map for the great Hawke's Bay earthquake of 1931. It will be seen that the intensity reached MM10 or higher in an area measuring about 50 miles by 25 miles, and the average radius for MM7 was about 65 miles.