Download Earthquakes - St Helens Park Public School

By Bethany Brewer
What is an earthquake?
Earthquakes are the sudden shock of the
earth’s surface. They are the Earth's natural
means of releasing stress. More than a million
earthquakes rattle the world each year. The
countries that are most at risk of having an
earthquake are unknown precisely, as
earthquakes can happen in many continents
and countries around the world. Earthquakes
can be felt over large areas although they
usually last less than one minute.
What causes earthquakes?
There are about 20 plates along the surface of
the earth that move slowly past each other.
When the rocks shift with great force, it causes
an earthquake. As the Earth’s tectonic plates
move they put forces on themselves and each
other. When the force is large enough, the crust
is obligated to break. When the break occurs,
the stress is released as energy which moves
through the Earth in the form of waves, which
we feel and call an earthquake.
Where do earthquakes
happen?
Within areas of the crust are fractures,
known as faults, along which two crustal
blocks have slipped or moved against each
other. One block may move up while the
other moves down, or one may move
horizontally in one direction and the other
in the opposite direction. Earthquakes occur
repeatedly at faults, which are zones of
weakness in the earth's crust.
Why does the earth shake during an
earthquake?
Earthquakes occur at the boundaries of
tectonic plates where stresses accumulate in
the Earth's crust, causing energy to be stored in
the form of elastic strain (like the elastic strain
in a spring). Ultimately this stress will ascend
the strength of the crust in the fault causing a
sudden brittle failure or rupture. This causes
movement and a sudden release of the stored
elastic strain energy in the form of waves (as
well as heat) causing an earthquake. These
waves cause the ground motions or shaking.
What are ‘after shocks’?
Aftershocks are “mini” earthquakes that follow
the largest shock of an earthquake sequence.
They are smaller than the main shock and
within 1-2 rupture lengths distance from the
main shock. Aftershocks can continue over a
period of weeks, months, or years. In general,
the larger the main shock, the larger and more
numerous the aftershocks, and the longer they
will continue.
How is a ‘Tsunami’ related to an
earthquake?
When earthquakes happen underwater, they
cause the ground level to rise and therefore
cause water to flow largely in one
direction. This makes an extremely large
and deadly tidal wave which then crashes
into and destructs whatever is in it’s path.
On 26th December, 2004, a deadly and
tragic tsunami hit many islands in the
Pacific Ocean killing at least 275,950
people including children.
How do scientists measure
earthquakes?
There are two ways which scientists use to measure
earthquakes. They measure the severity of the
earthquake, using the Richter scale and they
measure the damage caused by the earthquake,
using the Mercalli scale. The Richter scale works by
taking readings of vibrations caused by
earthquakes. The vibrations are calculated through
a mathematical device which then is measured from
0 to 10+. The Mercalli scale measures the strength
of an earthquake kind of like the Richter Scale but
this scale uses the observations of the people who
witnessed the earthquake to estimate its intensity on
a scale from1 to 12.
Can scientists predict
earthquakes?
Earthquakes cannot be predicted - although
scientists are working on it! Scientists were
convicted in Italy for failing to predict a deadly
earthquake. But no one can predict when an
earthquake will happen, or how big it will be. There
are increased amounts of data, new theories and
powerful computer programs and scientists are using
those to explore ways that earthquakes might be
predicted in the future. We can certainly hope that
someday we’ll be in a world where an earthquake
can be predicted before it occurs and give us time to
move away from it to reduce deaths.
What environmental impact do
earthquakes have?
Earthquakes have many environmental
impacts on our earth including the deaths of
people and sometimes, animals. Also many
natural things are affected largely like
landslides, tsunamis, ground failure, seiche
and many secondary effects such as broken
water pipes, hazardous material spills and
electrical and gas pipe leaks.
Bibliography
http://www.weatherwizkids.com
http://wiki.answers.com
http://earthsky.org
http://www.ehow.com
http://images.google.com.au
http://www.animationfactory.com
http://answers.askkids.com
And my own knowledge!!!!
Earthquakes
Thank you Mr Knobel and
students!!
Please note that these were real
life pictures of tragic tsunamis
and earthquakes around the
world and many people lost
their lives.