Earthquake Scales

The intensity of an earthquake can be described by three main scales:

Moment Magnitude (Mw) - Based on energy released (logarithmic scale)
Mercalli Intensity - Based on actual observations of damage (cannot be measured by instruments)
Richter Magnitude (ML) - Based on the movement of a needle (logarithmic scale)

Important Note: The Mercalli scale measures local shaking while the Richter scale measures total energy in the whole earthquake. These scales are not directly convertible.

Classification	Mercalli Intensity	Richter Magnitude	Moment Magnitude	Observations
Instrumental	I	2	1.0 - 3.0	Micro earthquakes, usually not felt - detected by instruments
Feeble	II	2	3.9	Often felt, especially on upper floors - detected by instruments
Slight	III	3	4.0	Felt noticeably indoors, vibration like passing vehicles, cars may rock
Moderate	IV	-	4.9	Felt indoors by many, felt outdoors by few. Dishes and doors disturbed, like a heavy truck nearby, walls-cracking sound
Rather Strong	V	4	5.0	Felt by most people, slight damage. Some dishes and windows broken, some cracked plaster, trees disturbed
Strong	VI	5	5.9	Felt by all, many frightened and run outdoors. Damage minor to moderate
Very Strong	VII	5 - 6	6.0	Everyone runs outdoors. Much damage to poor designed buildings, some chimneys broken, noticed by people driving cars
Destructive	VIII	6	6.9	Damage moderate to major. Minor damage to well designed structures, major damage in poor designed structures. Chimneys, columns and walls fall. Heavy furniture turned. Well water changes, sand and mud ejected
Ruinous	IX	7	7.0	Can cause serious damage over larger areas. Major damage in all structures, ground cracked, pipes broken, shift foundation
Disastrous	X	7 - 8	-	Major damage, most masonry and frame structures destroyed. Ground badly cracked, landslides, water sloshed over river banks, rails bent
Very Disastrous	XI	8	-	Almost all masonry structures destroyed, bridges fall, big fissures in ground, land slumps, rails bent greatly
Catastrophic	XII	>8	-	Devastating in areas several thousand miles across. Total destruction, Ground surface waves seen, objects thrown in the air. All constructions destroyed

Classification

Mercalli Intensity

Richter Magnitude

Moment Magnitude

Observations

Instrumental

1.0 - 3.0

Micro earthquakes, usually not felt - detected by instruments

Feeble

3.9

Often felt, especially on upper floors - detected by instruments

Slight

III

4.0

Felt noticeably indoors, vibration like passing vehicles, cars may rock

Moderate

4.9

Felt indoors by many, felt outdoors by few. Dishes and doors disturbed, like a heavy truck nearby, walls-cracking sound

Rather Strong

5.0

Felt by most people, slight damage. Some dishes and windows broken, some cracked plaster, trees disturbed

Strong

5.9

Felt by all, many frightened and run outdoors. Damage minor to moderate

Very Strong

VII

5 - 6

6.0

Everyone runs outdoors. Much damage to poor designed buildings, some chimneys broken, noticed by people driving cars

Destructive

VIII

6.9

Damage moderate to major. Minor damage to well designed structures, major damage in poor designed structures. Chimneys, columns and walls fall. Heavy furniture turned. Well water changes, sand and mud ejected

Ruinous

7.0

Can cause serious damage over larger areas. Major damage in all structures, ground cracked, pipes broken, shift foundation

Disastrous

7 - 8

Major damage, most masonry and frame structures destroyed. Ground badly cracked, landslides, water sloshed over river banks, rails bent

Very Disastrous

Almost all masonry structures destroyed, bridges fall, big fissures in ground, land slumps, rails bent greatly

Catastrophic

XII

Devastating in areas several thousand miles across. Total destruction, Ground surface waves seen, objects thrown in the air. All constructions destroyed