# Teachers' notes

The student materials consist of a series of practical activities which model seismological processes and activities carried out by seismologists.

The key ideas are:

• When an earthquake occurs, some of the stress build-up is released and results in slippage.
• Energy is transferred through the Earth via seismic waves; P-waves are longitudinal waves and S-waves are transverse waves. Earthquakes also generate more complex 'surface waves' that travel along the Earth's surface. It is usually the surface waves that have the largest amplitudes and do the most damage to buildings.
• Seismometers allow us to detect and monitor earthquakes by converting vibrations due to seismic waves into a visible, measurable output; in modern seismometers this usually involves converting vibrations into electrical signals which we can then display as seismograms on a computer screen.
• The arrival time of seismic waves at different seismic stations depends on their distance from the earthquake's origin. Seismologists use these differences and knowledge of the speeds of different seismic waves to work out the exact location of an earthquake's source.
• Every structure has
• a natural frequency of vibration. When an earthquake makes a structure vibrate at this frequency, the vibrations are much larger than at other frequencies.
Modelling an earthquake

Students use a brick and sandpaper to model the characteristics of earthquakes. They record the amount of slip produced each time the brick moves, and the force before and after each slip.

Understanding seismic waves

Students use a model based on wire helical coils ('slinkies') to look at how an earthquake generates P-waves and S-waves.

Detecting vibrations

Students use a magnet and coil and sound-editing software to detect vibrations.

How do seismologists locate an earthquake?

Students investigate the effect of different 'earthquake' positions on the signals received by two 'seismic stations', using two microphones connected to a PC with sound-editing software.

What does a seismogram show?

Students identify some features of a real seismogram.

Identifying features of a seismogram

Students identify some features on real seismograms and/or use these seismograms to consider differences in arrival times of P- and S-waves at different stations.

How earthquakes affect buildings

Students use a shake table to investigate the effects of earthquakes on structures.

Looking at data from several stations

Students examine data from several stations at the same time, using a 'record section'.

Designing a seismometer

Students use a seismometer modelling kit to design and build a more realistic model seismometer.

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