Earthquakes

Why do earthquakes occur? Where do earthquakes occur? How do we measure earthquakes?

An earthquake occurs when rocks inside the crust move suddenly An earthquake occurs when rocks inside the crust move suddenly. The FOCUS is where this happens. The EPICENTRE is the place on the surface directly above the focus There are 3 types of shock waves that come from an earthquake. P waves (push or primary waves) make the rocks move up and down S waves (shake or secondary waves)make the rocks move from side to side L waves (long waves) spread out in waves along the surface – they are the slowest but most destructive

Why do earthquakes occur?

Measuring and recording earthquakes. Seismometer Seismograph

The shock waves are detected on seismographs The magnitude of an earthquake is measured on the Richter Scale

Constructive plate boundary (Divergent) The crust is being forced apart. This puts tension on rocks and eventually they will crack and move apart resulting in an earthquake.

Destructive plate boundary(Convergent) One crustal plate is forced down below another. The friction between the plates is immense and stops the plates from moving. Eventually the pressure builds up and the crust jerks downwards into the mantle. This sudden movement causes and earthquake.

Transforming Boundaries Crustal plates slide past each other. No crust is destroyed or constructed and no volcanic activity takes place. The sliding movement is not smooth. Because of the friction between the two plates, they are locked together most of the time. When the pressure builds up over a long period it is great enough to overcome the friction which results in an earthquake.

P waves and S waves Vibrations from an earthquake are categorised as P or S waves. They travel through the Earth in different ways and at different speeds. They can be detected and analysed.

P waves and S waves P and S waves A wave is a vibration that transfers energy from one place to another without transferring matter (solid, liquid or gas). Light and sound both travel in this way. Energy released during an earthquake travels in the form of waves around the Earth. Two types of seismic wave exist, P- and S-waves. They are different in the way that they travel through the Earth.

P waves and S waves P-waves (P stands for primary) arrive at the detector first. They are longitudinal waves which mean the vibrations are along the same direction as the direction of travel. Other examples of longitudinal waves include sound waves and waves in a stretched spring. S-waves (S stands for secondary) arrive at the detector of a seismometer second. They are transverse waves which mean the vibrations are at right angles to the direction of travel. Other examples of transverse waves include light waves and water waves.

S waves cause more damage during an Earthquake because of the way that they move. They cause building to shake from side to side and this causes them to fall more easily.

P waves and S waves http://www.bbc.co.uk/schools/gcsebitesize/science/21c/ear th_universe/seismic_wavesrev1.shtml

P waves and S waves http://www.bbc.co.uk/schools/gcsebitesize/science/21c/ear th_universe/seismic_wavesrev1.shtml

Predicting and preparing for earthquakes In your groups: Write down ideas on how to predict and prepare for earthquakes.