NJDEP - New Jersey Geological and Water Survey - Modified Mercalli Intensity Scale of 1931

Modified Mercalli Intensity Scale of 1931¹
Mercalli
Intensity
Equivalent
Magnitude²
Effects

I

1.9 Not felt except by a very few under especially favorable circumstances.

II 2.5 Felt only by a few persons at rest, especially on upper floors of buildings.
Delicately suspended object may swing.

III 3.1 Felt quite noticeably indoors, especially on upper floors of building but
many people do not recognize it as an earthquake. Standing motorcars
may rock slightly. Vibration like passing of truck. Duration estimated.

IV

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

V

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

VI 4.9 Felt by all, many frightened and run outdoors. Some heavy furniture
moved; a few instances of fallen plaster or damaged chimneys.
Damage slight.

VII 5.5 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.

VIII 6.1 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. Persons
driving motorcars disturbed.

IX

6.7 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.

X

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

XI 7.9 Few, if any, (masonry) structures remain standing. Bridges destroyed.
Broad fissures in ground. Underground pipelines completely out of
service. Earth slumps and land slips in soft ground. Rails bent greatly.

XII 8.5 Damage total. Waves seen on ground surfaces. Lines of sight and level
distorted. Objects thrown upward into air.

**Modified Mercalli Intensity Scale of 1931¹**
Mercalli Intensity	Equivalent Magnitude²	Effects
I	1.9	Not felt except by a very few under especially favorable circumstances.
II	2.5	Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended object may swing.
III	3.1	Felt quite noticeably indoors, especially on upper floors of building but many people do not recognize it as an earthquake. Standing motorcars may rock slightly. Vibration like passing of truck. Duration estimated.
IV	3.7	During the day, felt indoors by many, outdoors by few. At night, some awakened. Dishes, windows, doors disturbed; walls make creaking sound. Sensation like heavy truck striking building. Standing motorcars rocked noticeably.
V	4.3	Felt by nearly everyone, many awakened. Some dishes, windows, etc., broken; a few instances of cracked plaster; unstable objects overturned. Disturbances of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop.
VI	4.9	Felt by all, many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster or damaged chimneys. Damage slight.
VII	5.5	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.
VIII	6.1	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. Persons driving motorcars disturbed.
IX	6.7	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.
X	7.3	Some well--built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides considerable from riverbanks and steep slopes. Shifted sand and mud. Water splashed (slopped) over banks.
XI	7.9	Few, if any, (masonry) structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipelines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly.
XII	8.5	Damage total. Waves seen on ground surfaces. Lines of sight and level distorted. Objects thrown upward into air.

1 Abridged (Wood and Neumann, 1931). Wording is that of Wood and Neumann. Effects on
cars, trucks and buildings built according to modern standards may be different.

2 Magnitude values were estimated using the formula: magnitude = 1.3 + (0.6 maximum
intensity).