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Earthquakes
Seismic Waves in the Earth’s Crust
Earthquakes
► An
earthquake is a series of seismic waves or
tremors in the earth’s crust.
► They
are caused when pressure builds up at the
edge of the plates as they collide or slide past one
another.
► When
this pressure is released a huge amount of
energy is released causing the plates to shake.
This shaking movement is the earthquake.
Earthquakes – Important Words
► Tremors
– These are the waves of seismic
energy which spread out from the Focus.
► Aftershocks
– These are the smaller tremors
which may occur hours or days after the
original earthquakes. They can also be
extremely dangerous because they may
cause already damaged buildings to
collapse.
The Focus and the Epicentre
► Focus
– This is the
place deep in the
earth’s crust where the
earthquake begins.
► Epicentre
– This is the
place on the surface of
the earth, directly
above the Focus. The
tremors are strongest
at this point.
Measuring Earthquakes
►
The strength or force of an
earthquake is measured on
a Seismograph.
►
The scale used to describe
this force is called the
Richter Scale. 1 is the
weakest and 10 is the
strongest.
►
Each point on the Richter Scale means that an earthquake is 10 times
stronger. For e.g. and earthquakes measuring 6 on the scale is 10 x
stronger than an earthquake measuring 5 on the scale.
Earthquakes – The San Andreas Fault
What happens along the San
Andreas Fault?