1. Earthquakes and Earth’s Interior
Chapter 8

2. Earthquakes Vibration of Earth produced by the rapid release of energy
Focus
Point within Earth where the shaking begins
Epicenter
is the location on the surface directly above the focus
Faults
Fractures in Earth where movement has occurred

3. Epicenter & Focus

4. Faults

5. Cause of Earthquakes
Rocks undergo stress and begin to bend storing up elastic energy
Eventually the friction cannot keep the elastic energy in check and the rock snaps.
Known as the Elastic Rebound Hypothesis

6. Elastic Rebound Hypothesis

7. Earthquakes Foreschocks Aftershocks
Days or years before a major earthquake
Small
Follow a major earthquake
Weaker than the major earthquake

8. Measuring Earthquakes
Seismographs
Instruments that record earthquake waves
Seismograms
Paper/ data from the seismograph

9. Seismograph

10. Seismogram

11. Earthquake Waves Surface Waves Body Waves
Move in up down and side to side motions
Side to Side motion most damaging
Most destructive earthquake waves
Arrive at recording stations last
P waves
Push-pull waves
Compression waves
Quickest wave
S waves
Shake the particles at right angles to their direction of travel
Called transverse waves
Can not pass through gas or liquid

12. Wave Animation
Earthquake Waves

13. Locating an Earthquake
Can be found using the differences between P and S wave speed
The greater the difference in arrival time between P and S waves the farther from the epicenter
Three seismograph stations are needed
Called triangulation

14. Triangulation

15. Travel Time Graph

16. Earthquake Zones 95% of major earthquakes occur in a few narrow zones
Near the outer edge of the Pacific Ocean (Circum-Pacific belt) Japan, Philippines, Chile, Alaska
Around the Mediterranean Sea (Mediterranean-Asian belt)
Mid-Atlantic Ridge

17. World Seismic Activity

18. Measuring Earthquakes
Intensity
Magnitude
Measure of the amt of earthquake shaking at a given location
Based on the amount of damage
Measure the size of seismic waves of amount of energy released
Rely on calculations using seismograms

19. Richter Scale Used on Television news reports not used by scientists
10 times stronger for every increase on the scale
5 earthquake is 10 times stronger than a 4

20. Modified Mercalli Scale
Measures damage
Information gathered by surveying people in the area

21. Mercalli Scale

22. Moment Magnitude Most widely used measurement for earthquake
Estimates the energy released by an earthquake

23. Moment Magnitude

24. Seismic Vibrations
Damage to buildings and other structures for earthquake waves depends on intensity and duration of vibrations and the material the structure is built on and the design of the structure

25. Predicting Earthquakes
Earthquakes CANNOT be predicted

26. Buildings
Wood is better than concrete, bricks etc (more flexible)

27. Haiti January 2010

28. Chile February 2010

29. Chile February 2010

30. Northridge, CA January 1994

31. Liquefaction
When loosely compacted sediments are saturated with water, stable soil behaves like a liquid
When areas are backfilled causes problems
Causes large amounts of damage to buildings

32. Liquefaction
Liquefaction

33. Liquefaction
Caused most damage in San Francisco Earthquake

34. Sand Boils
Loma Prieta

35. Tsunamis Seismic sea waves
Triggered when a slab of the ocean floor is displaced along a fault
Can occur when the vibration of a quake set an underwater landslide into motion (Indonesia 2006)

36. Indonesia 2004

37. Japan Tsunami 2011

38. Japan Tsunami 2011

39. Tsunami Warning System
Earthquakes register to the Tsunami Warning Center in Hawaii
Check water heights and issue warnings

40. Tsunami Warning Systems

41. Tsunami Warning Buoy

42. Tsuanami Warning Signs

43. Earth’s Layers Chemical Composition
3 major zones based on chemical composition
Crust
Mantle
Core

44. Crust Thin rocky outer layer Continental Crust Oceanic Crust
8-75 km thick
Over 4 billion years old
Oceanic Crust
7 km thick
180 million years old or less

45. Mantle Solid, rocky shell that extends to a depth of 2890 km
82% of Earth’s volume

46. Core
Sphere composed of iron and nickel

47. Layers Defined Physical Properties
Lithosphere
Outermost layer (100km thick)
Crust and upper mantle
Asthenosphere
Lower mantle
Weak layer
Outer core
Liquid layer
Inner core
Solid layer (due to pressure)

48. Discovering Earth’s Layers
Earth’s layers were discovered by studying seismic waves