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Modified Mercalli Scale
Earthquakes and relevant
trigger thresholds
MM Degree Accel (cm/s2)
Description
1
1
2
2
3
3
Not felt by many people unless in favourable conditions.
Felt by a people at rest, especially on the upper floors of buildings or in
favourable position
Felt by people indoors. Hanging objects swing. Vibration like passing of
light trucks. Duration estimated. May not be recognized as an earthquake
Hanging objects swing. Vibration like passing of heavy trucks, or
sensation of a jolt like a heavy ball striking the walls. Standing motor cars
rock. Windows, dishes, doors rattle. Glasses clink. Crockery clashes.
In its upper range, wooden walls and frame creak.
4
15-20
5
30-40
6
60-70
7
100-150
8
250-300
9
500-550
10
>600
11
-----
12
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Felt outdoors; direction estimated. Sleepers wakened. Liquids disturbed,
some spilled. Small unstable objects displaced or upset. Doors swing,
close, open. Shutters, pictures move. Pendulum clocks stop, start,
change rate.
Felt by all. Many frightened and run outdoors. Persons walk unsteadily.
Windows, dishes, glassware broken. Knickknacks, books, etc., off shelves.
Pictures off walls.
Furniture moved or overturned. Weak plaster and
masonry D cracked. Small bells ring (church, school).
DETECTOR TRIGGERED
Difficult to stand. Noticed by drivers of motor cars. Hanging objects quiver.
Furniture broken. Damage to masonry D, including cracks. Weak chimneys
broken at roof line. Fall of plaster, loose bricks, stones, tiles, cornices (also
unbraced parapets and architectural ornaments). Some cracks in masonry
C. Waves on ponds; water turbid with mud. Small slides and caving in along
sand or gravel banks. Large bells ring. Concrete irrigation ditches damaged.
Steering of motor cars affected. Damage to masonry C; partial collapse.
Some damage to masonry B; none to masonry A. Fall of stucco and some
masonry walls. Twisting, fall of chimneys, factory stacks, monuments,
towers, elevated tanks. Frame houses moved on foundations if not bolted
down; loose panel walls thrown out. Decayed piling broken off. Branches
broken from trees. Changes in flow or temperature of springs and wells.
Cracks in wet ground and on steep slopes.
General panic. Masonry D destroyed; masonry C heavily damaged,
sometimes with complete collapse; masonry B seriously damaged; general
damage to foundations; frame structures, if not bolted, shifted off
foundations; frames racked. Serious damage to reservoirs.
Underground pipes broken. Conspicuous cracks in ground. In alluvial areas
sand and mud ejected, earthquake fountains, sand craters.
Most masonry and frame structures destroyed with their foundations.
Some well-built wooden structures destroyed with their foundations. Some
well-built wooden structures and bridges destroyed. Serious damage to
dams, dikes, embankments. Large landslides. Water thrown on banks of
canals, rivers, lakes, etc. Sand and mud shifted horizontally on beaches
and flat land. Rails bent slightly.
Damage nearly total. Large rock masses displaced. Lines of sight and level
distorted. Objects thrown into the air.
Rails bent greatly. Underground pipelines completely out of service.
