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The Modified Mercalli Intensity Scale





3.0 to 3.9
4.0 to 4.9
IV to V
5.0 to 5.9
6.0 to 6.9
7.0 to 7.9
IX to X
8.0 to 8.9

The Modified Mercalli Intensity Scale was developed in 1931 by American seismologists Harry Wood and Frank Neumann. The scale, composed of 12 levels of intensity that range from imperceptible shaking to catastrophic destruction, is designated by Roman numerals. The scale is not mathematically based, but rather a ranking based on observed effects. Why it is called the "Mercalli" scale is not clear.

  • I — Not felt by people, except rarely under especially favorable circumstances.
  • II — Felt indoors only by persons at rest, especially on upper floors. Some hanging objects may swing.
  • III — Felt indoors by several people. Hanging objects may swing slightly. Vibration feels like passing of light trucks. May not be recognized as an earthquake.
  • IV — Felt indoors by many, felt outdoors by few. Hanging objects swing. Vibration feels like passing of heavy trucks or sensation of a jolt like a heavy ball striking the walls. Standing automobiles rock. Windows, dishes, doors rattle. Wooden walls and frame may crack.
  • V — Felt indoors by nearly everyone. Liquids disturbed, some spilled. Small unstable objects displaced or upset, some dishes and glassware broken. Doors swing, shutters, and pictures move. Pendulum clocks stop, start, or change rate. Swaying of tall trees and poles sometimes noticed.
  • VI — Felt by all. Damage slight. Persons walk unsteadily. Windows, dishes, and glassware broken. Knickknacks and books fall off shelves. Furniture moved or overturned. Weak plaster and masonry cracked.
  • VII — Difficult to stand. Damage negligible in buildings of good design and construction, slight to moderate in well-built ordinary buildings, considerable in badly designed or poorly built buildings. Noticed by drivers of automobiles. Hanging objects quiver. Furniture broken. Weak chimneys broken. Damage to masonry. Small slides and caving in along sand or gravel banks. Large bells ring.
  • VIII — People frightened. Damage slight in specially designed structures, considerable in ordinary substantial buildings, great in poorly built structures. Steering of automobiles affected. Damage or partial collapse to some masonry and stucco. Failure of some chimneys, factory stacks, monuments, towers, and elevated tanks. Frame houses moved on foundations if not bolted down. Decaying pilings broken off. Branches broken from trees. Changes in flow or temperature in springs and wells. Cracks in wet ground and on steep slopes.
  • IX — General panic. Damage considerable in specially designed structures, great in substantial buildings with some collapse. General damage to foundations. Frame structures, if not bolted, shifted off foundations and thrown out of plumb. Serious damage to reservoirs. Underground pipes broken. Conspicuous cracks in ground.
  • X — Most masonry and frame structures destroyed with their foundations. Some well-built wooden structures and bridges destroyed. Serious damage to dams, dikes, and embankments. Landslides on river banks and steep slopes considerable. Water splashed onto banks of canals, rivers, lakes. Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly.
  • XI — Few, if any, masonry structures remain standing. Bridges destroyed. Broad fissures in ground. Earth slumps and landslides widespread. Underground pipelines completely out of service. Rails bent greatly.
  • XII — Damage nearly total. Waves seen on ground surfaces. Large rock masses displaced. Lines of sight and level distorted. Objects thrown upward into the air.

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