| # |
What happens to people and
structures |
| I |
Not felt except by a very few persons 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 passing
truck. |
| IV |
During the day, felt in doors by many, outdoors
by few. At night, some awakened, Dishes, windows, doors disturbed;
walls make creaking sound. Sensation like heavy truck striking
building. Standing motor cars rocked noticeably. |
| V |
Felt by nearly everyone; many awakened.
Some dishes, windows, etc., broken; a few instances of cracked
plaster; unstable objects overturned. Disturbances of trees, poles,
and other tall objects sometimes noticed. Pendulum clocks may
stop. |
| VI |
Felt by all, many frightened and run outdoors.
Some heavy furniture moved; a few instances of fallen plaster
or damaged chimneys, Damage slight. |
| VII |
Everybody runs 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 cars. |
| VIII |
Damage slight in specially designed 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 in small
amounts. Changes in well-water levels. Disturbs persons driving
motor 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 foundations. Ground cracked conspicuously.
Underground pipes broken. |
| X |
Some well built wooden structures destroyed;
most masonry and frame structures destroyed with foundations;
ground badly cracked. Rails bent. Landslides considerable from
river banks and steep slopes. Shifted sand and mud. Water splashed
over banks. |
| XI |
Few, if any, masonry structures remain standing.
Bridges destroyed. Broad fissures in ground. Underground pipelines
completely out of service. Earth slumps and land slips in soft
ground. Rails bent greatly. |
| XII |
Damage total. Waves seen on ground surfaces.
Lines of sight and level distorted. Objects thrown upward into
the air. |
There are two
basic ways to measure the strength of an earthquake; magnitude and intensity.
Magnitude measures the total amount of energy released in an earthquake.
Intensity measures of the effect of an earthquake on buildings and reactions
of people. No instruments are used to determine intensity, just interviews
with people in the affected area and observations of damaged structures.
It is a useful measure in built-up urban areas, but not so useful in remote
areas without any buildings to damage or people to react! 