AN EARTHQUAKE’S INTENSITY – THE MODIFIED
MERCALLI INTENSITY SCALE
O’Brien, Principal Planner, NJOEM
does it feel when a earthquake shakes?
... It depends on where you are.
earthquake can be measured by the amount of energy released.
The Richter scale uses Arabic numbers to rate the amount
of energy, or its magnitude.
size or strength of an earthquake may be measured by
the intensity or kind of damage that occurs. Intensity
depends on your distance from the epicenter and the
geologic area. The Modified Mercalli scale measures
the earthquake’s effect on people, property and
ground damage. Roman numerals are used to rate the intensity
earthquake may have a different intensity rating at
different locations. Damage is usually lessened with
distance from the earthquake’s epicenter. However,
damage may depend on the type of structure, construction,
or type of soil on which the structure was built. For
example, a building on bedrock experiences less movement
than a building on loose sediments.
Modified Mercalli (MM) scale reads as follows:
Not felt except by a very few under especially favorable
lying down might feel the earthquake. Light suspended
objects may sway.
on upper floors will feel it, but may not know it’s
an earthquake. Hanging objects swing.
indoors will probably feel it, but those outside may
not. Houses may creak.
everybody feels it. Sleepers are awakened. Doors swing,
pictures move, things tip over.
feels the earthquake. It is hard to walk. Windows
and dishes broken. Books fall from shelves.
is hard to stand. Plaster, bricks and tiles fall from
buildings. Small landslides.
will not be able dive cars. Poorly built buildings
may collapse, chimneys may fall.
foundations are damaged. Masonry heavily damaged.
Pipes are broken. The ground cracks.
buildings are destroyed. Water is thrown out of rivers
and lakes. Large landslides.
are bent. Bridges and underground pipelines unusable.
objects are leveled. Large objects may be thrown into
the air. Large rock masses displaced.
Relationship Between Magnitude and Intensity
(close to epicenter)