1. Chapter 19 - Earthquakes
19.1- Forces within Earth

2. Earthquakes Result of movement of crust produced by Plate tectonics
Stress = total force acting on crustal rocks
Builds up overtime
Overcomes strength of rocks and causes movement along fractures in rock
Earthquake = vibrations caused by movement in crust

3.
Stress
Three types
Compression – decrease volume of material
Tension – pulls material apart
Shear – causes material to twist
Strain = deformation of material in a response to stress

4. Deformation
Elastic – when a material is compressed, bent, or stretched
at low stress
Material can return to “normal” when stress is zero
Example: Pulling on a rubber band

5. Deformation Plastic – stress builds up past elastic limit
Permanent deformation – stays changed even when stress is zero
Point of Rupture = failure
Example: Pulling rubber band until it breaks

6. Deformation
Most materials exhibit varying degrees of plastic and elastic deformation

7. Faults Any fracture or system of fractures along which Earth moves
Happens along weak regions
Fault plane = surface along which movement takes place

8.
Faults
Reverse Fault – form as a results of horizontal and vertical compression that squeezes rock
Seen near convergent plate boundaries
Two areas end up closer together after faulting

9. Faults Normal fault – movement partly horizontal and partly vertical
Faults
Normal fault – movement partly horizontal and partly vertical
Horizontal movement pulls rocks apart and stretches crust
Vertical movement causes one side of rock to move down relative to the other side
Two areas end up farther apart after faulting

10. Faults Strike-slip fault – caused by horizontal shear
Faults
Strike-slip fault – caused by horizontal shear
Movement is mainly horizontal in opposite direction
Example: San Andreas Fault
Creates offset features after movement

11. Earthquake waves
Seismic waves = vibration of the ground produced during an earthquake
Primary waves = squeeze and push rocks in same direction wave is traveling
Secondary waves = cause rocks to move at right angles relative to wave direction
Slower than P waves
Surface waves = cause most destruction and take longest to past
Slowest wave, only travel of Earth’s surface

12. Seismic Waves

13. Earthquake Focus = point where waves originate
Epicenter = point on surface directly above focus

14. In-Class Assignment/Homework