Download Earthquakes

Earthquakes
What is an Earthquake?
•It is a sudden movement called a tremor in the Earth’s Crust.
•It is caused by the release of pressure which causes shock (or seismic ) waves
No one knows exactly how Earthquakes are formed but they happen along Tectonic
Plate Boundaries and when they happen a lot of energy is released.
What is a Tectonic Plate boundary? The Earth’s crust is like a giant jigsaw. This map shows you
where the plates are
The tectonic plates are a bit like closely packed iceburgs that move against
each other very slowly
Where Do Earthquakes occur?
Earthquakes occur along Tectonic Plate boundaries
Comparing the Tectonic Plate map
with the map showing where
Earthquakes occur you can see
that the two show identical
patterns.
A huge amount of energy builds
up as plates try to move in
different directions and when
they eventually do move they
release this energy as an
Earthquake tremor. To give you
some idea of the energy levels….
How strong are Earthquakes?
What causes Earthquakes?
When tectonic plates move it is a bit like giant icebergs slowly moving past each
other in a sea crowded with icebergs so the plates either move away from each
other, towards each other or slide past each other.
Plates are pulling apart
Plates are moving towards each other
Plates are sliding past each other
What causes Earthquakes?
As two plates slide against each other it is not a smooth action- they push against each
other then suddenly slip. This causes shock waves like a drop of water falling into a puddle.
Tectonic plates slide past each
other – this is not smooth
Shockwaves radiate
outwards
Strike-slip fault – notice how the furrows in this ploughed field have been
moved out of line
ACTIVITY 1 Modelling an Earthquake using a brick and pulley.
The area of the brick in contact with the plank represents the fault. Winding the pulley
increases the force representing the build-up of stress in the fault. You will be looking
at the level of force needed to move the brick and the distance the brick travels
Shock waves or tremors radiate from the Earthquakes focus.
Shock waves
Radiate like rings in a puddle becoming less
strong as they get further away
There are two main types of waves produced by an Earthquake
Longitudinal
or P wave
Transverse or
S wave
ACTIVITY 2
Making waves
You will be using slinkies to represent the waves produced by
an Earthquake looking at the speed at which different waves
travel
How do we measure Earthquakes?
Old fashioned Seismometers looked like this with a large suspended weight which remains
stationery whilst the surrounding apparatus moves with the vibrations caused by the tremor.
The spring amplifies the movement so that it can be recorded directly on the chart attached to
the revolving drum. Modern Seismometers work on a similar principle but instead of using a
pen the signal is converted into voltages and then into digital data streams and can be viewed
on a computer screen.
ACTIVITY 3- making seismometers
Using the kits you can build your own seismometer and see how well it picks up
vibrations on the desk.
A weight is suspended here by a
boom. A strong magnet is
attached to the boom and this is
placed next to a coil. As the
ground vibrates the magnet moves
in and out of the coil inducing a
change in voltage which the
computer picks up as a trace that
you can see.
Earthquakes cause a great deal of damage, injury and death. One of the biggest hazards comes from falling buildings.
The frequency of the tremor from an Earthquake will affect the way structures vibrate
and break. Some simple techniques can be used in building to help make them
Earthquake -proof.
ACTIVITY 4- Earthquake proof buildings and shake tables.
The shake-table vibrates in
a similar way to
Earthquake tremors and
you can vary the
frequency. Consider how
height and weight
distribution affects the
vibration.
Given some straws and
blue tack you are
challenged to make a small
two storey structure that
can withstand the shake
table.
What have you learnt?
What did the brick and pulley show us? How do your results compare with real
Earthquake data?
What did you learn from the slinkies?
How many different seismometers did you make? How successful were they?
Did you make any straw buildings that could withstand the shake table?
Any questions you’d like to ask us?
Real Earthquake data for Earthquakes during 2000 to 2006- note shape of the bar chart? Does
it look like our bar chart? What does this tell us about Eathquakes?