Geology Reference
In-Depth Information
TABLE
6.1
Modified Mercalli Intensity Scale of 1931.
Intensity
Description of Effects
I
Not felt by people, except under especially favorable circumstances. Sometimes birds and animals are
disturbed. Trees, structures, liquids, and bodies of water may sway gently, and doors may swing slowly.
II
Felt indoors by a few people, especially on upper floors of multistory buildings. Birds and animals are
disturbed, and trees, structures, liquids, and bodies of water may sway. Hanging objects may swing.
III
Felt indoors, usually as a rapid vibration that may not be recognized as an earthquake at first, similar to
that of a light truck passing nearby. Movements may be appreciable on upper levels of tall structures.
IV
Felt indoors by many, outdoors by few. Awakens a few individuals. Characterized by vibration like that
due to passing of heavy or heavily loaded trucks, a heavy body striking building, or the falling of heavy
objects inside. Dishes, windows, and doors rattle. Walls and house frames creak. Hanging objects
often swing. Liquids in open vessels are disturbed slightly. Stationary automobiles rock noticeably.
V
Felt indoors by practically everyone, outdoors by most people. Awakens many or most sleepers.
Frightens a few people; some persons run outdoors. Buildings tremble throughout. Dishes and glass-
ware break to some extent. Windows crack in some cases, but not generally. Vases and small or
unstable objects overturn in many instances. Hanging objects and doors swing generally. Pictures
knock against walls, or swing out of place. Pendulum clocks stop, or run fast or slow. Doors and shut-
ters open or close abruptly. Small objects move, and furnishings may shift to a slight extent. Small
amounts of liquids spill from well-filled containers.
VI
Felt by everyone, indoors and outdoors. Awakens all sleepers. Frightens many people; there is gen-
eral excitement, and some persons run outdoors. Persons move unsteadily. Trees and bushes shake
slightly to moderately. Liquids are set in strong motion. Plaster cracks or falls in small amounts. Many
dishes and glasses, and a few windows, break. Books and pictures fall. Furniture may overturn or
heavy furnishings move.
VII
Frightens everyone. There is general alarm, and everyone runs outdoors. People find it difficult to
stand. Persons driving cars notice shaking. Trees and bushes shake moderately to strongly. Waves form
on ponds, lakes, and streams. Suspended objects quiver. Damage is negligible in buildings of good
design and construction; slight to moderate in well-built ordinary buildings; considerable in poorly
built or badly designed buildings. Plaster and some stucco fall. Many windows and some furniture
break. Loosened brickwork and tiles shake down. Weak chimneys break at the roofline. Cornices fall
from towers and high buildings. Bricks and stones are dislodged. Heavy furniture overturns.
VIII
There is general fright, and alarm approaches panic. Persons driving cars are disturbed. Trees shake
strongly, and branches and trunks break off. Sand and mud erupt in small amounts. Flow of springs
and wells is changed. Damage slight in brick structures built especially to withstand earthquakes; con-
siderable in ordinary substantial buildings, with some partial collapse; heavy in some wooden houses,
with some tumbling down. Walls fall. Solid stone walls crack and break seriously. Chimneys twist and
fall. Very heavy furniture moves conspicuously or overturns.
IX
There is general panic. Ground cracks conspicuously. Damage is considerable in masonry structures
built especially to withstand earthquakes; great in other masonry buildings, with some collapsing in
large part. Some wood frame houses built especially to withstand earthquakes are thrown out of
plumb, others are shifted wholly off foundations. Reservoirs are seriously damaged, and underground
pipes sometimes break.
X
Most masonry and frame structures and their foundations are destroyed. Ground, especially where
loose and wet, cracks up to widths of several inches. Landsliding is considerable from riverbanks and
steep coasts. Sand and mud shift horizontally on beaches and flat land. Water level changes in wells.
Water is thrown on banks of canals, lakes, rivers, etc. Dams, dikes, and embankments are seriously
damaged. Well-built wooden structures and bridges are severely damaged, and some collapse. Rail-
road rails bend slightly. Pipelines tear apart or are crushed endwise. Open cracks in cement pavements
and asphalt road surfaces.
XI
Few if any masonry structures remain standing. Broad fissures, earth slumps, and land slips develop in
soft wet ground. Water charged with sand and mud is ejected in large amounts. Sea waves of signifi-
cant magnitude may develop. Damage is severe to wood frame structures, especially near shock cen-
ters, great to dams, dikes, and embankments, even at long distances. Supporting piers or pillars of
large, well-built bridges are wrecked. Railroad rails bend greatly and some thrust endwise. Pipelines
are put out of service.
