1. Seismic waves
4.6 Recall that seismic waves are generated by earthquakes or explosions
4.9 Recall that seismic waves can be longitudinal (P) waves and transverse (S) waves and that they can be reflected and refracted at boundaries between the crust, mantle and core
4.11 Demonstrate an understanding of how P and S waves
travel inside the Earth including reflection and refraction (H)

2. Japanese earthquake (2011)

3. Crust - a thin layer of rock (like the shell of a egg)
Structure of the Earth
Crust - a thin layer of rock (like the shell of a egg)
Mantle mostly solid rock but also contains molten rock called magma
Inner core
(solid)
made of nickel and iron
Outer core
(liquid)
made of nickel and iron.

4. Main activity
P-waves and S-waves

5. Explain the differences between the seismic waves, P-waves and S-waves
Explain the differences between the seismic waves, P-waves and S-waves. How has the study of these waves helped us to understand about the structure of the Earth?
Key words
Longitudinal
Transverse
Fastest
Liquid
Solid
Shadow zone
Refracted
Primary
Secondary

7. Plate tectonics
Most (but not all) earthquakes happen at the boundaries between tectonic plates

10. Seismic waves P waves: S waves:
When an Earthquakes happens SEISMIC WAVES are generated. They travel through the body of the Earth. There are two types of seismic wave:
P waves:
They are longitudinal
They can pass through solids and liquids
They go faster than S waves
S waves:
They are transverse
They ONLY pass through solids
They are slower than P waves

11. Seismic waves
As P waves travel through the Earth they are refracted, making us think it is made up of different layers.
S waves will only
travel through a solid
Shadow zone – S or P waves not detected here!

12. Seismic waves S waves will only travel through a solid
P waves travel through the Earth and are refracted when they pass through a medium
The paths of these waves are all curved because density is gradually changing
These observations tell us 3 things about the Earth: 1) It has a thin crust, 2) it has a semi-fluid mantle where density increases with depth, 3) a core with a liquid outer part and a solid inner part.

14. Using Seismometers to detect location of earthquakes

15. Time difference between the arrival of P waves and S waves can be used to find out the distance from epicentre.

16. Data from 3 or more seismometers can be used to locate the epicentre of the earthquake; this is called TRIANGULATION.