1. Lithosphere-Earthquakes Unit

2. Why earthquakes happen?
Earthquakes occur when rocks fracture, or break, deep within Earth
Fractures form when stress exceeds the strength of the rocks involved

3. Three Types of Stress compression-decreases volume tension-pulls apart
shear-twists material

4. Elastic Rebound
Stress causes the ground begins to be deformed. An earthquake occurs when a rock passes its point of maximum elasticity. After it breaks, it regains its original shape (but not position.)

5. Faults
Many rocks fail when stress is applied too quickly or when stress is great
Resulting fracture along which movement occurs is called a fault

6. Three Types of Faults
Reverse faults – form due to compression, shortens crust Normal faults – form due to tension extends crust Strike-slip faults – form due to shear

7. Faults

8. Focus and Epicenter
Focus – where the fracture occurs to cause an earthquake, beneath Earth’s surface; the closer focus is to Earth’s surface, the more severe the damage is to be expected.
Epicenter – the spot on the surface above the focus

9. Seismograph
A device used to measure seismic waves in the Earth’s interior .
Seismogram-written record of a seismograph.

10. Seismic Waves Vibrations of an earthquake Three types of waves:
Primary waves (P waves)
Secondary waves (S waves)
Surface waves

11. P Waves
P waves (primary)-push and pull rocks in same direction wave travels; fastest seismic wave.
Animation

12. S Waves
S waves (secondary)-moves rocks at right angles to direction of wave’s travel.
Animation

13. Surface Waves
Surface waves-travel on Earth’s surface, in both directions of p and s waves; slowest seismic waves, cause most damage.

15. What P and S waves can tell us
By comparing the time difference between the arrival of P and S waves, the epicenter of an earth quake can be located
It has also been determined that Earth’s outer core is molten through observation of P and S waves

16. P Wave Shadow Zone
P and S waves can both travel through solids and move in direct patterns in the mantle.
P waves that strike the liquid outer core alter direction, creating an area where no P waves appear on a seismogram called the P wave shadow zone.

17. P Wave Shadow Zone
S waves that strike the core do not pass through. S waves cannot travel through liquid, which led scientists to believe the Earth’s outer core was molten.

19. So, match the correct seismogram below with its location1 2 3 4 5 D A E C B

20. Finding the Epicenter Three seismograph stations are needed. Why?
Each location gives us a distance, so we can draw a circle there. Then the intersection of 3 circles gives us the epicenter.

21. How could you tell the epicenter if you only had two seismographs?

22. Richter Scale
Magnitude-a measurement of energy released by an earthquake.
Richter scale-a numerical scale based on size of largest seismic wave generated by a quake that describes its magnitude.
Higher the number, higher the magnitude.

24. Historical Earthquakes

25. Changing earthquake depth at subduction zones
Why do the earthquakes vary in depth?
Which way is the plate subducting at the Tonga Trench?
To the west
Which way is the plate subducting at the Peru-Chile Trench?
To the east

26. Let’s look at the Tonga Trench
Deepening earthquakes at a subduction zone

27. Tsunami
A series of ocean waves caused by sudden displacement in the ocean floor .

28. Tsunami travel times to Hawaii

29. Old Tsunami Photo