1. Earthquakes

2. Earthquakes
Earthquakes are natural vibrations of the ground, caused by:
Fractures in earth’s crust
Volcanic eruptions

3. Stress and Strain Stress causes fractures in rock
Three types of stress:
Compression
Tension
Shear
Deformation caused by stress is known as strain

4. Compression
Compression is stress that decreases the volume of material

5. Tension
Tension is stress that pulls a material apart

6. Shear
Shear is stress that causes a material to twist

7. Effects of Strain and Stress
Stress and strain can cause deformation
Low stresses cause elastic strain
Elastic strain causes a material to bend and stretch
Can return to normal, like a rubber band
High stresses cause ductile deformation
Material is permanently deformed
Can cause breaks or failure

8. Faults When stress causes rock to fail, a fault occurs
Fault – Fracture(s) along which movement occurs
Three main types of faults:
Reverse
Normal
Strike-Slip (Transform)

9. Reverse Fault
Reverse Faults are fractures that result from horizontal compression
Shortens crust horizontally

10. Normal Fault Normal Faults are fractures caused by horizontal tension
Lengthens crust horizontally

11. Strike-Slip Fault
Strike-Slip Faults are fractures caused by horizontal shear
Motion is mainly horizontal

12. Earthquake Waves
Vibrations of the ground during earthquakes are called Seismic Waves
Three types:
Primary Wave (P-Wave)
Secondary Wave (S-Wave)
Surface Waves

13. P-Waves
P-Waves squeeze and pull rocks in the same direction as the wave travels

14. S-Waves
S-Waves cause rocks to move at right angles to the direction of the wave

15. Surface Waves
Surface Waves move rocks up and down, as well as side-to-side
Motion is similar to an ocean wave

16. Focus Earthquakes originate at a point called a Focus
Focus is usually below the surface
The Epicenter is the point on Earth’s surface directly above the focus