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FAQ for Earthquake

7. What is "intensity"?

The intensity of an earthquake is a measure of the degree of vibration that people can feel on the Earth's surface, or the degree of damage for an object under vibration.

Today seismic apparatus is able to portray detailed earthquake acceleration, such that the intensity can be classified according to the information on the acceleration. Scales of the earthquake intensities exist as positive numbers (see Earthquake Intensity Table by the Central Weather Bureau, Ministry of Transportation and Communications).

Earthquake Intensity Table
Central Weather Bureau, Ministry of Transportation and Communications

Intensity Scale Ground Acceleration(cm/s2,gal) Effects on People Effects Indoors Effects Outdoors
0 Micro Below 0.8
Not felt.
1 Very minor 0.8~2.5
Felt only by a few people at rest, vibrates slightly.
2 Minor 2.5~8.0
Felt by the majority of people. Some awakened from sleeping.
Hanging lamps and objects vibrate slightly.
Standing vehicles vibrate slightly, similar to being passed by a truck, but only lasts for a short time.
3 Light 8~25
Felt by nearly everyone, a few frightened.
Buildings shake; dishes, windows, and doors shake making sounds; hanging objects shake visibly.
Standing vehicles vibrate obviously; electric wires sway gently.
4 Moderate 25~80
Many people are quite frightened, looking for safe shelter. Most people are awakened from sleep.
Buildings rock noticeably; unstable objects topple over; heavy furniture moves; may cause slight damage.
Felt by drivers; electric wires sway obviously, felt by people walking.
5 Strong 80~250
Most people are considerably frightened.
Walls crack; heavy furniture may overturn.
Noticeably felt by drivers; some chimneys and large archways topple over.
6 Very Strong 250~400
People have trouble walking due to violent rocking.
Damage to some buildings; heavy furniture overturns; doors and windows bend.
Drivers have trouble steering; sand and clay blasts occur.
7 Great 400 and above
People move with difficulty due to severe rocking.
Severe damage to or collapse of some buildings; almost all furniture moves or falls down.
Landslides and faults rupture occur; railway bend; underground lines break.