Whats
New?
The Mercalli Scale of earthquake damage measures
the intensity of an earthquake at a particular
place. It uses the type and amount of damage.
Unlike the Richter Scale, it does not measure
the absolute strength of the earthquake, but
how strongly it is felt at a particular place.
This makes the Mercalli Scale useful in comparing
damage from different quakes.
and
afterward, the plates or blocks of rock start
moving, and they continue to move until they
get stuck again. The spot underground, where
the rock breaks is called the focus of the
earthquake.
How
are Earthquakes measured?
The Richter scale is used to measure the amount
of energy released in a given earthquake.
Richter readings are useful in comparing earthquakes
that occur in different times and places.
The larger the Richter reading, the greater
the damage will be close to the epicenter.
In recent years, scientists have used a variety
of magnitude scales to measure different aspects
of an earthquake. These different scales sometimes
lead to confusion.
An observer near the epicenter of an earthquake
will generally experience 3 or 4 on the Richter
Scale as a mild shaking, 5 or 6 will be enough
to cause some damage, 7 will cause a lot of
damage and 8 or higher will cause tremendous
destruction.
A look at the 4 largest quakes of
the century.
| Chile |
May 22, 1960 |
9.5 |
| Aleutian
Islands |
Mar 9, 1957 |
9.1 |
| Sumatra,
Indonesia |
Dec. 26, 2004 |
9.0 |
| Rat
Islands, Aleutian Islands |
Feb. 4, 1965 |
8.7 |
What
are its affects?
The ramifications of a quake are manifold
including fire, injury and loss to life and
property.
Fire:
Fires often break out following earthquakes.
They can be caused by flammable materials,
cooking or broken gas lines. Fires can easily
get out of control since the earthquake may
have broken water mains or blocked roads firefighters
need to use.
Building Collapse:
People can be trapped in collapsed buildings
or under rubble that collapses into the street.
This is the type of damage that leads to the
worst casualties. The worst thing to do in
a quake is to rush out into the street during
the quake. The danger from being hit by falling
glass and debris is many times greater in
front of the building than inside.
Landslides:
Buildings can be damaged when the ground
gives way beneath them. This can be in the
form of a landslide down a hill, or liquefaction
of soils that can cause severe settling of
the ground.
Tsunami:
Underwater earthquakes can produce a tsunami
or tidal wave. This wave can travel very rapidly
thousands of miles across the ocean. As it
approaches land, the shallower water causes
the wave to build in height to as much as
50 feet or more and suddenly floods the coastal
areas. Tsunamis carry a lot of energy and
when they hit the coast, strong currents can
cause massive erosion of the coastline as
well as tearing apart buildings it encounters.
Typically a tsunami will last for a period
of hours with successive waves drastically
lowering and raising the sea level. A tsunami
is a large wave caused by an abrupt displacement
of water, very similar to the ripples from
a rock thrown into the water. Unfortunately,
some of the worst tsunamis occur near the
epicenter of the originating earthquake and
therefore give little warning.
Earthquakes can be devastating.
From time immemorial its affects have been
felt through generations proving that despite
science and its progress the hand of Nature
prevails.
