1. Earthquakes and Earth’s Interior
Chapter 8
Earthquakes and Earth’s Interior

2. Chapter 8.1 Objectives
Earthquakes
Compare and Contrast the epicenter and focus of an earthquake
Indentify the cause of earthquakes using the elastic rebound hypothesis.
Explain what a fault is.
Compare and contrast aftershocks and foreshocks.

3. 6.1 What Is an Earthquake? Earthquakes earthquake vibration of Earth
release of energy
Focus
Origin of Earthquake
Epicenter
Surface point directly above the focus
Faults
Fractures in E. where movement occurs

4. Focus, Epicenter, and Fault

5. Slippage Along a Fault

6. 6.1 What Is an Earthquake? Cause of Earthquakes
 Elastic Rebound Hypothesis
rapid release of elastic energy stored in rock
When strength of rock is exceeded it breaks
Vibrations are caused by the break

7. Elastic Rebound Hypothesis

8. 6.1 What Is an Earthquake? Cause of Earthquakes
 Aftershocks and Foreshocks
Aftershock
_____________________
foreshock
_______________________

9. Chapter 8.2 Objectives
Measuring Quakes
Identify 3 types of seismic waves and know how each moves.
Explain how to locate the epicenter of an earthquake.
Describe the different ways a Quake is measured.
Know the difference between a seismograph and seismogram.

10. 8.2 Measuring Earthquakes
Earthquake Waves
8.2 Measuring Earthquakes
 Seismographs -
 Seismograms -

11. Seismograph

12. Seismogram

13. 8.2 Measuring Earthquakes
3 types of Earthquake Waves
8.2 Measuring Earthquakes
P waves
- P
- Travel through ________ ___________ & ___________
- Speed -__________________

14. 8.2 Measuring Earthquakes
Earthquake Waves
8.2 Measuring Earthquakes
S waves
Travel along outer surface
- Shake particles -
- Travel only through _____________
- Speed-

15. 8.2 Measuring Earthquakes
Types of Earthquake Waves
8.2 Measuring Earthquakes
Surface waves are seismic waves that travel along Earth’s outer layer.
A seismogram
shows all three types of waves

16. Seismic Waves

17. 8.2 Measuring Earthquakes
Locating an Earthquake
8.2 Measuring Earthquakes
Locating Epicenter
Using the difference in the arrival times between P and S wave
3 seismographs are needed
• About 95 percent of the major earthquakes occur in a few narrow zones.

18. Locating an Earthquake

19. 8.2 Measuring Earthquakes
Two factors—
Intensity
magnitude
Richter Scale- NOT USED BY SCIENTISTS
• Based on largest seismic wave
• 32-fold energy increase per #
• Not good for large earthquakes

20. 8.2 Measuring Earthquakes
 Momentum Magnitude Scale
amount of displacement
Surface Area of Fault
Size of Wave
Only scale that estimates total Amount of energy released
• Measures very large earthquakes

21. Earthquake Magnitudes

22. Some Notable Earthquakes

23. Chapter 8.3 Objectives
Measuring Quakes
Describe 4 factors that contribute to earthquake destruction.
Explain 3 other dangers associated with Earthquakes.
Explain the potential for earthquake prediction & explain seismic gap.
Be able to calculate the earthquake probability for various locations using the internet.

24. 8.3 Destruction from Earthquakes
Seismic Vibrations
8.3 Destruction from Earthquakes
Damage depends on
Intensity
Duration
material on which the structure is built
design of structure
unreinforced stone & brick are worst

25. Earthquake Damage

27. 8.3 Destruction from Earthquakes
Seismic Vibrations
8.3 Destruction from Earthquakes
 Liquefaction
• Saturated material turns fluid
• Underground objects may float to surface

28. Effects of Subsidence Due to Liquefaction

29. Effects of Subsidence Due to Liquefaction

30. 8.3 Destruction from Earthquakes
Tsunamis
8.3 Destruction from Earthquakes
 Cause of Tsunamis
tsunami
slab of the ocean floor is displaced vertically along a fault and wave results
Can be caused by underwater landslide.
• Tsunami is the Japanese word for “seismic sea wave.”

31. Movement of a Tsunami

32. 8.3 Destruction from Earthquakes
Tsunamis
8.3 Destruction from Earthquakes
 Tsunami Warning System
• Large earthquakes are reported to Hawaii from Pacific seismic stations.
• Although tsunamis travel quickly, there is sufficient time to evacuate all but the area closest to the epicenter.

33. 8.3 Destruction from Earthquakes
Other Dangers
8.3 Destruction from Earthquakes
Landslides
Greatest damage
Ground Subsidence
Sinking of ground
Caused by vibrations
Fire
San Francisco 1906
Gas, electrical, water lines severed

34. Landslide Damage

35. 8.3 Destruction from Earthquakes
Predicting Earthquakes
8.3 Destruction from Earthquakes
 Short-Range Predictions
• Not yet possible
 Long-Range Forecasts
• NO predictions, only probabilities
seismic gap
where there has not been any earthquake activity for a long period of time.

36. Earth’s Layers List the 3 main layers of earth based on composition.
Chapter 8.4 Objectives
Earth’s Layers
List the 3 main layers of earth based on composition.
List & describe 5 layers of the Earth based on physical properties.
Explain how Earthquakes help us understand the Earth’s layers.

37. 8.4 Earth’s Layered Structure
Layers Defined by Composition
8.4 Earth’s Layered Structure
 Three major zones
 Crust
• Thin, rocky outer layer
• thickness varies
- 7 km in oceanic
- 8–40 km continental
- Exceeds 70 km in mountain

38. 8.4 Earth’s Layered Structure
Layers Defined by Composition
8.4 Earth’s Layered Structure
 Crust cont.
• Continental crust
- Upper - granitic rocks
- Lower - basaltic
- density is about 2.7 g/cm3
- Up to 4 billion years old

39. 8.4 Earth’s Layered Structure
Layers Defined by Composition
8.4 Earth’s Layered Structure
 Crust cont.
• Oceanic crust
- Basaltic composition
- Density about 3.0 g/cm3
- Younger (<180 million yrs)

40. Seismic Waves Paths Through the Earth
animation

41. 8.4 Earth’s Layered Structure
Layers Defined by Composition
8.4 Earth’s Layered Structure
 Mantle
Below crust
to a depth of 2900 kilometers
Composition
Upper mantle - peridiotite

42. 8.4 Earth’s Layered Structure
Layers Defined by Composition
8.4 Earth’s Layered Structure
 Core
• Below mantle
• Sphere with a radius of 3486 kilometers
• Composed of an iron-nickel alloy
• Average density of nearly 11 g/cm3

43. 8.4 Earth’s Layered Structure
Layers Defined by Physical Properties
8.4 Earth’s Layered Structure
 Lithosphere
• Crust and uppermost mantle (about 100 km thick)
• Cool, rigid, solid
 Asthenosphere
• Beneath the lithosphere
• Upper mantle
• To a depth of about 660 kilometers
• Soft, weak layer that is easily deformed

44. 8.4 Earth’s Layered Structure
Layers Defined by Physical Properties
8.4 Earth’s Layered Structure
 Lower Mantle
• 660–2900 km
• More rigid layer
• Rocks are very hot and capable of gradual flow.

45. 8.4 Earth’s Layered Structure
Layers Defined by Physical Properties
8.4 Earth’s Layered Structure
 Inner Core
• Sphere with a radius of 1216 km
• Behaves like a solid
 Outer Core
• Liquid layer
• km thick
• Convective flow of metallic iron within generates Earth’s magnetic field

46. Earth’s Layered Structure

47. 8.4 Earth’s Layered Structure
Discovering Earth’s Layers
8.4 Earth’s Layered Structure
 Moho ˇ
• Velocity of seismic waves increases abruptly below 50 km of depth
• Separates crust from underlying mantle
 Shadow Zone
• Absence of P waves from about 105 degrees to 140 degrees around the globe from an earthquake
• Can be explained if Earth contains a core composed of materials unlike the overlying mantle

48. Earth’s Interior Showing P and S Wave Paths

49. 8.4 Earth’s Layered Structure
Discovering Earth’s Composition
8.4 Earth’s Layered Structure
 Crust
• Early seismic data and drilling technology indicate that the continental crust is mostly made of lighter, granitic rocks.
 Mantle
• Composition is more speculative.
• Some of the lava that reaches Earth’s surface comes from asthenosphere within.

50. 8.4 Earth’s Layered Structure
Discovering Earth’s Composition
8.4 Earth’s Layered Structure
 Core
• Earth’s core is thought to be mainly dense iron and nickel, similar to metallic meteorites. The surrounding mantle is believed to be composed of rocks similar to stony meteorites.