Modified Mercalli earthquake intensity scale

The Mercalli scale is used to estimate the effects of an earthquake at a particular locality. The intensity experienced, therefore, depends on both the magnitude of the easrthquake (a measure of the energy released at the hypocenter) and the distance of the locality from the hypocenter.

 

Intensity

Effects

I Not felt, except by a very few people under especially favorable circumstances.

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

III Felt quite noticeably indoors, especially on upper floors, but many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibration like that caused by a passing truck.

IV During the day, felt indoors by many people, outdoors by few. At night some people are awakened. Crockery, windows, doors are disturbed; walls make a creaking sound. Sensation like that caused by a heavy truck striking the building. Standing motor cars rocked noticeably.

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

VI Felt by all many people are frightened and run outdoors. Some heavy furniture moved: a few instances of fallen plaster or damaged chimneys. Damage is slight.

VII Many people run 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 motor cars.

VIII Damage is slight in specially designed(l 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 from the ground in small amounts. Changes in water levels in wells. Earthquake disturbs even persons who are driving cars.

IX 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 their foundations. Ground cracks conspicuously. Underground pipes are broken.

X Some well-built wooden structures are destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides considerable in the vicinity of river banks and steep slopes. Sand and mud deposits are shifted. Water splashed over banks.

XI Few, if any, masonry structures remain standing. Bridges destroyed. Broad fissures in the ground. Underground pipelines completely out of service. Earth slumps and landslips occur in soft ground. Rails bent greatly.

XII Damage is total. Waves seen on ground surface. Lines of sight and level distorted. Objects thrown upwards into the air.