1. P1H Smart Teach 3

2. Write Down
Frequency – means the number of vibrations or waves passing in one seconds.
Humans can only hear sounds with a frequency from 20Hertz to 20,000Hertz.
Infrasound – sound too low in pitch to hear with a frequency below 20Hertz
Ultrasound – sound too high in pitch to hear with a frequency above 20,000Hertzs.

3. Transverse vs. longitudinal waves
18/04/2016
Displacement
Transverse waves are when the displacement is at right angles to the direction of the wave.
Direction
Examples – light, other EM waves, some seismic waves
Displacement
Longitudinal waves are when the displacement is parallel to the direction of the wave…
Direction
Examples – sound, some seismic waves

4. Write Down
Longitudinal waves are waves where the vibrations are parallel to the direction the wave travels.
e.g. Infrasound, ultra sound, sound, P Seismic waves.

7. Key Point- Outer core is liquid!
Before you look in more detail about earthquakes you first need to understand the structure of the earth
Key Point- Outer core is liquid!
The Earth is almost a sphere. These are its main layers, starting with the outermost:
crust - relatively thin and rocky
mantle - has the properties of a solid, but can flow very slowly
outer core - made from liquid nickel and iron
inner core - made from solid nickel and iron
Note that the radius of the core is just over half the radius of the Earth. The core itself consists of a solid inner core and a liquid outer core.

8. Tectonic Plates?
The outermost layer of the Earth is made up of tectonic plates.
These plates
are slowly
moved by
convection
currents.

9. Write Down
Earthquakes are caused by sudden movement of the Earth’s Tectonic Plates in the Crust.
The plates are moved by the Convection Currents in the hot mantle below.
Hot Mantle – Rising
Cold Mantle - Sinking

10. Convection currents can lead to earthquakes...
Radioactive decay takes place in the mantle, this produces a lot of heat, which causes the mantle to flow in convection currents. The hot rock rises then cools, causing the plates to move. As the plates move they slide past each other. There is friction between the plates. Sometimes they get stuck, the pressure and energy builds up. Eventually they slip releasing the energy as an earthquake.

11. Key Point- Seismic waves like any other waves will refract!
These are waves that travel through the earth when an earthquake occurs. You need to learn the properties of the two types of waves.
Key Point- Seismic waves like any other waves will refract!

12. Key Points
S waves cannot pass through the liquid outer core, but P waves can. When P waves pass from solid to liquid, then from liquid to solid, there are sudden changes in direction – they are reflected and refracted. Seismic waves are also reflected and refracted as they pass into different rock types.

13. Questions about Earthquakes will often ask you to calculate time or distance a wave has travelled.
You will use the following equation to answer them:
Wave speed = distance
time
Always show all working for calculations:
1 write down the equation used.
2 substitute the numbers into the equation.
3 check the units are correct for each number, convert them if needed to the correct units.
4 Write down the answer with its unit.

17. Write Down
Seismometers detect the P Seismic and S seismic waves from Earthquakes.
P seismic waves travel faster than S waves so are detected by Seismometers first.
The time difference between P and S seismic waves, known as S-P time, tells us how far an Earthquake epicentre is from a seismometer.
The larger the time difference is between P and S seismic waves arriving the further away the Epicentre is.

18. Write Down
Triangulation can be used with 3 or more Seismometers to locate the Epicenter of an Earthquake.

24. Write Down
Seismic waves do not travel in straight lines as they pass through the Earth.
Some waves are reflected at boundaries between layers.
Some waves are refracted as they pass from layer to layer.
The pathways seismic waves take travelling through the Earth have told us about its layered structure.