1. The Earth’s Crust Seismic Waves
Friday, November 23, 2018Friday, November 23, 2018

2. There are three kinds of seismic waves produced by an earthquake:

3. 1. P - waves – “primary waves” - the fastest waves (they are compression waves)
They can travel through solids, liquids, and gasses.

4. 2. S - waves “secondary waves – these are slower than p waves and occur as a side to side wave.
These waves travel only through solids.

5. 3. L- waves – “long waves” or “surface waves”.
These waves travel as a double wave along the surface of the earth.
They are the slowest waves but they cause the most damage.

7. Locating Earthquakes
The time between the p-wave and the s-wave is used to calculate how far away the earthquake is.

8. Let’s say station #1 knows the earthquake happened 200 kms away.

9. Let’s say station #1 knows the earthquake happened 200 kms away.

10. But 200 kms in what direction?

11. If a second station reports it as 75 kms away, they can draw a circle and see where it intercepts the first circle.

12. But that still doesn’t pinpoint the location – it could have happened at either spot where the two circles touch.

13. But a third station removes all doubt as to where it happened.

14. But a third station removes all doubt as to where it happened.

15. Three seismographs are needed to pin- point the source of an earthquake.
Seismograph video

16. Focus – the place deep in the crust where the earthquake begins (source of primary and secondary waves)

17. Epicentre – the surface location directly above the focus (source of surface waves)

18. Tsunami – a tidal wave caused by an underwater earthquake
subduction tsunami
Once and future tsunamis
Tsunami
Tsunami – open ocean

19. tsunami

20. Tsunami devastation

27. Pacific Tsunami