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 wavesRadiate like rings in a puddle becoming less strong as they get further away

Longitudinal or P waveTransverse or S wave

There are two main types of waves produced by an Earthquake

Shock waves or tremors radiate from the Earthquakes focus.

ACTIVITY 2Making 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 seismometersUsing 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?