Earthquake Scales

Earthquake Scales - Mercalli Intensity, Richter Magnitude and Moment Magnitude

The intensity of an earthquake can be described by scales as :

Mercalli intensity

Richter magnitude (ML)

Moment magnitude (M_W)

	Mercalli Intensity	Richer Magnitude	Moment Magnitude	Actual Observation of the Earthquake
Instrumental	I	2	1.0 - 3.0	Microearthquakes, 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	Everyone runs outdoors. Damage moderate to major. Minor damage to well designed structures, major damage in poor designed structures. Chimneys, columns and walls falls. 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.

Description :

Mercalli Intensity - based on actual observations of the damage - can not be measured on instruments

Richter Magnitude - based on the movement of a needle - logarithmic sc

Moment Magnitude - based on energy released - logarithmic scale