USGS Intensity Scale

USGS Earthquake Learn page


USGS Seismic Intensity
level description table

USGS
intensity

I

Perceived Shaking: NOT FELT
Comments
Not felt except by a very few under especially favorable conditions.
Peak Ground Acceleration
Less than 0.0005 g (g = 9.81 m/s²)

USGS
intensity

II

Perceived Shaking: WEAK
Comments
Felt only by a few people at rest, especially on upper floors of buildings.
Peak Ground Acceleration
0.003 g (g = 9.81 m/s²)

USGS
intensity

III

Perceived Shaking: WEAK
Comments
Felt quite noticeably by people indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.
Peak Ground Acceleration
0.003 g (g = 9.81 m/s²)

USGS
intensity

IV

Perceived Shaking: LIGHT
Comments
Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
Peak Ground Acceleration
0.028 g (g = 9.81 m/s²)

USGS
intensity

V

Perceived Shaking: MODERATE
Comments
Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.
Peak Ground Acceleration
0.062 g (g = 9.81 m/s²)

USGS
intensity

VI

Perceived Shaking: STRONG
Comments
Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.
Peak Ground Acceleration
0.12 g (g = 9.81 m/s²)

USGS
intensity

VII

Perceived Shaking: VERY STRONG
Comments
Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.
Peak Ground Acceleration
0.22 g (g = 9.81 m/s²)

USGS
intensity

VIII

Perceived Shaking: SEVERE
Comments
Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.
Peak Ground Acceleration
0.40 g (g = 9.81 m/s²)

USGS
intensity

IX

Perceived Shaking: VIOLENT
Comments
Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.
Peak Ground Acceleration
0.75 g (g = 9.81 m/s²)

USGS
intensity

X

Perceived Shaking: EXTREME
Comments
Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.
Peak Ground Acceleration
More than 0.75 g (g = 9.81 m/s²)