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Faults and Earthquakes

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Presentation on theme: "Faults and Earthquakes"— Presentation transcript:

1 Faults and Earthquakes


3 Fracture - A crack or break in the Earth’s crust.

4 Fractures form when STRESS, the forces per unit area acting on a material, exceeds the strength of the rocks involved.

5 The deformation of materials in response to stress is called STRAIN.


7 Elastic Rebound

8 Stress and Strain ultimately lead to a fracture or a system of fractures, along which movement occurs, this is called a FAULT

9 Types of Faults Faults Are Classified According to the Kind of Motion That Occurs on Them

10 Strike-Slip - Horizontal Motion Dip-Slip – Vertical Motion

11 Strike-Slip Fault – Left Lateral

12 Strike-Slip Fault – Right Lateral

13 Normal Faults: Extension Reverse Faults: Compression
Dip-Slip Faults Normal Faults: Extension Reverse Faults: Compression Reverse Faults are often called Thrust Faults

14 Dip-Slip Fault - Normal

15 Normal Fault Structures

16 Dip-Slip Fault - Reverse

17 Reverse Fault Structures

18 Earthquakes Most Earthquakes are caused by movements along faults
Earthquakes Most Earthquakes are caused by movements along faults. Most Earthquakes occur along plate boundaries.

19 The location within the earth where a fault rupture actually occurs is called the FOCUS

20 The location on the surface directly above the focus is called the EPICENTER.

21 The vibrations of the ground during an earthquake are called SEISMIC WAVES.

22 Seismic Waves

23 Seismology - The study of Earthquake waves.

24 The sensitive instruments used to record the vibrations of earthquakes are called SEISMOGRAPHS or SEISMOMETERS.

25 The record produced by a seismometer is called a SEISMOGRAM
The record produced by a seismometer is called a SEISMOGRAM. This shows the arrival times of the different seismic waves at that location.

26 Primary waves or P-waves squeeze and pull rocks in the same direction along which the waves are traveling.

27 Secondary waves, or S-waves causes rocks to move up and down at right angles in relation to the direction of the waves.

28 P-waves are the fastest seismic waves
P-waves are the fastest seismic waves. Remember P comes before S in the alphabet.

29 Some Important Earthquakes
Lisbon, Portugal Killed 70,000 First Scientifically Studied Earthquake New Madrid, Missouri Felt over 2/3 of the U.S. Few Casualties

30 Some Important Earthquakes
Alaska Killed about 200 Wrecked Anchorage. Tsunamis on West Coast. Tangshan, China Hit an Urban Area of Ten Million People Killed 650,000

31 Major Hazards of Earthquakes
Building Collapse Landslides Fire Tsunamis (Not Tidal Waves!)

32 U.S. Seismic Risk

33 San Francisco and New Madrid Compared

34 Earthquakes (M.4)

35 U.S. Earthquakes 1973-2002 (28,332 events)

36 Seismology and Earth's Interior

37 Magnitude and Intensity
How Strong Earthquake Feels to Observer Magnitude Related to Energy Release Determined from Seismic Records Rough correlation between the two for shallow earthquakes

38 Magnitude How Much Energy is Released

39 Magnitude is measured using the Richter Scale

40 Richter scale Each successive number in the scale represents an increase in seismic-wave size, of a factor of 10.

41 Ex. A magnitude 7 earthquake is 10 times larger than a magnitude 6 earthquake.

42 Each increase in magnitude corresponds to a 32-fold increase in energy

43 Ex. A magnitude 7 earthquake releases 32 times more energy than a magnitude 6 earthquake.

44 Intensity How Strong an Earthquake Feels to the Observer

45 Depends On: Distance to Quake Geology Type of Building The Observer
Depends On: Distance to Quake Geology Type of Building The Observer! Varies from Place to Place

46 Intensity measured using the Mercalli Scale

47 Mercalli Scale - 1 to 12 a way of measuring earthquakes based on the amount of damage done.

48 Earth’s Interior as Inferred by Seismology

49 Discontinuity - any sudden change in the properties of a material

50 Earth’s Interior

51 CRUST- outer most layer; also known as the LITHOSPHERE

52 Two kind of crust: CONTINENTAL & OCEANIC

53 Comparing Continental to Oceanic Crust

54 Rocks made up of: Continental – Granite Oceanic - Basalt

55 Relative Thickness: Continental – Thicker Oceanic - Thinner

56 Relative Density: Continental – Less Dense Oceanic – More Dense

57 Relative Age: Continental – Older Oceanic - Younger

58 Moho – What is it? Boundary or interface between the CRUST and the MANTLE

59 The Moho was discovered by a change in seismic wave speed.

60 Mantle Region of dense material in the Earth’s interior between the CRUST and the OUTER CORE.

61 Asthenosphere Plastic-like part of the Upper Mantle

62 Core Broken into an Outer Core and an Inner Core

63 Outer Core It is a liquid… They know this because of a shadow zone in the P-waves

64 Shadow Zone Refraction of seismic waves creates an area on the Earth’s surface where no direct P-waves appear.

65 No S-waves pass through the outer core because they cannot pass through liquids.

66 Inner Core Solid - known because P-waves speed up

67 The inner core is believed to be composed of IRON and NICKEL

68 The overall structure of the Earth

69 Seismic Waves in the Earth

70 Inner Structure of the Earth


72 Based on the time it takes seismic waves to reach a location, the distance of that location can be determined using a P and S wave time travel graph.

73 Locating Earthquakes

74 Doing this for two stations show you 2 possible epicenters of the earthquake.

75 Locating Earthquakes

76 Using 3 or more stations will show you the location of the Epicenter

77 Locating Earthquakes

78 Locating Earthquakes - Depth

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