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Title: EARTHQUAKES


1
EARTHQUAKES
  • Dr. R. B. Schultz

2
Global Earthquake Locations
3
What are Earthquakes?
  • The shaking or trembling caused by the sudden
    release of energy
  • Usually associated with faulting or breaking of
    rocks
  • Continuing adjustment of position results in
    aftershocks
  • Shaking of earth due to movement of rocks along a
    fault.

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  • Rocks under stress accumulate strain energy over
    time.
  • When stress exceeds strength of rocks, rock
    breaks.
  • Strain energy is released as seismic waves. The
    longer that energy is stored up and is maintained
    without release, the more likely that a strong
    earthquake will occur.

6
The animation below of a subduction zone, where
an oceanic plate is converging with a continental
plate, attempts in cartoon fashion to show the
deformation of the continental plate that
precedes each earthquake.
7
  • What is FAULT?
  • A break or crack in rock along which movement of
    the earths crust occurs.
  • Can be visible on the crust or can be far
    underground.
  • Can be only a meter long or they can extend for
    hundreds of kilometers.

8
FAULT
9
Earthquakes can happen along any type of plate
boundary. They also occur along faults which are
large cracks in the earths crust. Most faults
are associated with large plate boundaries where
violent earthquakes usually occur.
10
  • Movement of rock along a fault can release a
    tremendous amount of energy This movement can
    release three main forces on adjoining areas of
    the crust
  • Tension results when a system of forces pulls
    or stretches an object from opposite sides.
  • Compression results when a system of forces
    pushes an object from opposite sides.
  • Shearing - results when a system of forces is
    applied to an object in different directions.

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13
What is the Elastic Rebound Theory?
All rocks have an elastic limit. If the forces
acting on these rocks exceed this limit, or
overcome the friction between blocks, the crust
snaps and an earthquake occurs.
14
What is the Elastic Rebound Theory?
  • Explains how energy is stored in rocks
  • Rocks bend until the strength of the rock is
    exceeded
  • Rupture occurs and the rocks quickly rebound to
    an undeformed shape
  • Energy is released in waves that radiate outward
    from the fault

15
KINDS OF FAULT
  • Normal Fault
  • one block can move down and the other can move
    up, or vice versa.
  • occurs where forces tend to pull section of the
    earths crust apart.
  • tends to follow the gravitational pull on the
    fault blocks involved.

16
  • The fault plane on the normal fault is generally
    very steep. In a normal fault the two involved
    blocks are (by gravity) pulling away from one
    another causing one of the fault blocks to slip
    upward and the other downward with respect to the
    fault plane (it is hard to determine whether both
    or just one block has moved.).

17
  • The exposed upward block forms a cliff-like
    feature known as a FAULT SCARP. A scarp may range
    from a few to hundreds of meters in height and
    their length may continue for 300 or more
    kilometers (around 200 miles).
  • FAULT SCARP landforms that form cliffs and
    ridges along the fault. (book definition)

18
Normal Fault
19
KINDS OF FAULT
  • 2. Thrust Fault
  • one block moves over another block
  • occurs where forces tend to push sections of the
    crust together.
  • When thrust faults are exposed on the surface
    overburnden material lies over the main block.
    They are normally associated with areas of folded
    surfaces and or mountaineous regions. The dip
    angles of thrust faults are normally not as steep
    as a normal fault. 

20
Thrust Fault
21
KINDS OF FAULT
  • 3. Strike-slip Fault (Transcurrent Fault)
  • the movement of the blocks is horizontal
  • known as the San Andreas fault of California.
    This fault marks the margin line between the
    Pacific and North American Plates. 
  • On the surface, scarps form as hills crossing the
    fault zone are torn apart by movement over time.

22
  • Actually anything crossing this fault zone is
    either slowly torn apart, or offset.
  • Rivers crossing the fault line are called offset
    streams and are classic signatures of fault
    activity along the San Andreas.
  • These faults can be very long, the San Andreas is
    nearly 600 miles long.

23
Strike-slip Fault
24
Three Types of Faults
Strike-Slip
Thrust
Normal
25
EARTHQUAKE AND PLATE TECTONICS
The lines on the map indicate plate boundaries.
26
The Focus and Epicenter of an Earthquake
  • The point within Earth where faulting begins is
    the FOCUS, or hypocenter
  • The point directly above the focus on the surface
    is the EPICENTER

27
Three Types of Focus
  • Shallow-focus
  • earthquake originates between the earths surface
    and a depth of 70 kilometers below the surface.
  • earthquakes in this class are detected at all
    three types of plate boundaries-trenches, ridges
    and fault boundaries.
  • most earthquakes have shallow focus.

28
Three Types of Focus
  • 2. Intermediate-focus
  • earthquake originates between 70 and 300
    kilometers beneath the surface.
  • 3. Deep-focus
  • earthquake originates 300 to 700 kilometers below
    the surface.
  • Both occurs at trench boundaries, where one plate
    moves under another.

29
Detecting Earthquakes
  • An earthquakes energy moves from the focus as
    Seismic Waves. (Sizmik)
  • These waves travel to all directions.
  • An earthquake generates 3 kinds of seismic waves.
  • These waves are
  • P-waves (Primary)
  • S-waves (Secondary)
  • L-waves (Surface)

30
Waves
  • In the illustration below, P-waves have the
    movement like that of Slinky. While S-waves have
    the movement of a snake or a rope. L-waves has
    movements of an ocean wave.

31
P or Primary Wave
  • The fastest seismic wave
  • Can travel through any material on earth- solid
    or liquid
  • P-waves compress and expand particles that lie on
    their path

32
S or Secondary Wave
  • It moves at half the speed of P-waves
  • Can travel only through solids
  • Movement within the earth resembles to wavelike
    motion that results when one shakes a stretched
    rope from side to side.

33
L or Surface Wave
  • The slowest wave
  • Moves along the earths surface
  • Causes most damage among all waves
  • Resembles thw motion of ocean waves.

34
Using Seismographs to Find the Epicenter
  • Seismograph- A sensitive instrument that measures
    and records seismic waves.

35
How does it work?
  • A seismograph has a heavy weight suspended from a
    support that is attached to bedrock. During an
    earthquake, inertia keeps the weight and the pen
    attached to it still. When a seismic wave passes,
    the support, base and revolving paper drum shake.
    Thus, the pen marks zigzag lines on a paper drum,
    recording the movements of the earth. The
    recorded lines are the...



36
Seismogram
  • A recording or the recorded lines of a
    seismograph.
  • In the figure below, there are 3 distinct groups
    of zigzag lines that correspond to the different
    kinds of seismic waves.

37
The Epicenter and the Seismogram
  • Scientists analyze the time difference between
    the arrival of the P and S waves.
  • By doing so, they can calculate the distance to
    the earthquakes epicenter.

38
How do they do it?
  • Note Please refer to the pictue at the past
    slide.
  • Readings from 3 seismograph stations are needed
    to locate the epicenter of the earthquake. Assume
    that a scientist calculates the distance from
    Station A to the epicenter to be 1000 km. The
    distance is determined on the difference of
    arrival time of the 2 waves. The scientist knows
    the distance of A to the epicenter. The scientist
    draws a circle on a map which has a radius the
    equivalent of 100 km. Meanwhile,Stations B and C
    determines the distance to be at 500 and 400 km,
    respectively. Again, they draw circles. The
    meeting point of the circles is the epicenter.

39
Seismic Waves and The Earths Interior
  • The seismic waves that result from an earthquake
    spread throughout the earth.
  • Geologists study the speed and the paths of
    seismic waves to learn about the earths
    interior.
  • Our knowledge of the earths layers relied on the
    changes in speed and direction of seismic waves.

40
Seismic Waves and The Earths Interior
  • Early in the century, geologists discovered that
    large areas on the side of the earth away from
    the earthquake focus do not receive waves. Look
    at the image below.

41
P-Waves and the Earths Interior
  • In the case of P-waves, they can pass through the
    mantle, the liquid outer core, and the solid
    inner core. Notice the small shadow zone at the
    image. It has been stated that P-waves can pass
    through all particles.

42
S-Waves and the Earths Interior
  • While at the S-waves, a large shadow zone is
    formed. Again, it has been staterd that S-waves
    can only pass through solids.
  • This discovery has enabled scientists to conclude
    that the outer core is liquid.

43
Types of Earthquake
  • 1. Tectonic type- earthquake that result from the
    upward and downward movements of the crustal
    plates due to pressure.
  • 2. Volcanic type- earthquakes produced by the
    pressure generated by magma rising through faults
    towards the earths surface.

44
Intensity
  • Intensity- measure of an earthquakes effect or
    damage in a place.
  • Modified Mercalli Scale named after Guiseppe
    Mercalli is used as a basis for the intensity of
    an earthquake.

45
Modified Mercalli Scale Intensity Scale-
Description
  • Intensity Scale- Description
  • I-Not felt
  • II-Felt by persons at rest
  • III- Felt indoors
  • IV- hanging objects swing
  • V- felt outdoors
  • VI- felt by all

46
Modified Mercalli Scale Intensity Scale-
Description
  • VII- difficult to stand
  • VIII- steering of cars affected
  • IX- general panic
  • X-most masonry and frame structures destroyed
    with their foundations
  • XI- rails bent gently
  • XII- damage nearly total

47
Magnitude Richter Scale
  • Magnitude- measures the energy released during
    quake by measuring the amplitude of the largest
    wave recorded on the seismogram
  • Richter Scale- named after Charles Richter used
    as basis for the magnitude. The scale is
    logarithmic, one point increases in the scale
    means tenfold increases

48
Richter ScaleMagnitude Scale- Description
  • 1- only detectable when an ultrasensitive
    seismometer
  • 2- hardly susceptible shocks
  • 3- very feeble shocks
  • 4- feeble shocks
  • 5- earthquakes with moderate strength

49
Ritcher ScaleMagnitude Scale- Description
  • 6- strong earthquakes
  • 7-major earthquakes
  • 8- great earthquakes
  • 9-never occurred

50
How are the Size and Strength of an Earthquake
Measured?
  • Intensity
  • subjective measure of the kind of damage done and
    peoples reactions to it
  • isoseismal lines identify areas of equal intensity
  • Modified Mercalli Intensity Map
  • 1994 Northridge, CA earthquake, magnitude 6.7

51
  • Measuring Earthquakes
  •  
  • The power (magnitude) of an earthquake is
    measured on the Richter scale, using an
    instrument called a seismometer.
  •  
  • The Richter scale is numbered 0-10 with 10 being
    the most powerful. The Richter scale is
    logarithmic an earthquake measuring 7 is 10
    times more powerful than one measuring 6 and 100
    times more powerful than one measuring 5. Up
    until 2 on the Richter Scale only instruments
    will detect the earthquake. Earthquakes above 6
    cause serious damage and sometimes many deaths
  •  
  • The Mercalli scale measures the damage caused by
    an earthquake. The Mercalli scale goes from I to
    XII e.g. VI. Everyone feels movement. People
    have trouble walking. Objects fall from shelves.
    Pictures fall off walls. Furniture moves. Plaster
    in walls might crack. Trees and bushes shake.
    Damage is slight in poorly built buildings. No
    structural damage.

52
How are the Size and Strength of an Earthquake
Measured?
  • Magnitude
  • Richter scale measures total amount of energy
    released by an earthquake independent of
    intensity
  • Amplitude of the largest wave produced by an
    event is corrected for distance and assigned a
    value on an open-ended logarithmic scale

53
Effects Of Earthquakes The Richter Scale
  • After an earthquake, its description usually
    includes a number from 1 to 9 in the Richter
    Scale.
  • This number indicates the magnitude or the total
    amount of energy released.

54
Charles F. Richter The Inventor
  • He was a geologist stationed at the California
    Institute Of Technology.
  • Before he invented it, earthquakes were measured
    at a much less scientific scale. Personal
    observations were made, and scientists had to use
    this to base their conclusions.
  • This method greatly reduced the guesswork in
    determining the magnitude of an earthquake.

55
What do earthquakes do to the Earth?
  • Earthquakes do a lot of effects on the earth.
    These include
  • Structural damage
  • Benito Juarez Hospital, Mexico City. (taken in
    1985)

56
What do earthquakes do to the Earth?
  • Tsunami, a Japanese word meaning harbor wave.
    These are really different from the actual harbor
    waves, but can do a significant amount of damage.

57
What Controls the Level of Shaking?
  • Magnitude
  • More energy released
  • Distance
  • Shaking decays with distance
  • Local soils
  • amplify the shaking

58
Is there such a thing as Earthquake Weather???
No!
59
Earthquake Effects - Ground Shaking
Northridge, CA 1994
60
Earthquake Effects -Ground Shaking
Northridge, CA 1994
61
Earthquake Effects - Ground Shaking
Loma Prieta, CA 1989
KGO-TV News ABC-7
62
Earthquake Effects - Ground Shaking
Kobe, Japan 1995
63
Earthquake Effects - Ground Shaking
Kobe, Japan 1995
64
Earthquake Effects - Surface Faulting
Landers, CA 1992
65
Earthquake Effects - Liquefaction
Source National Geophysical Data Center
Niigata, Japan 1964
66
Earthquake Effects - Landslides
Source National Geophysical Data Center
Turnagain Heights, Alaska,1964 (upper left
inset) Santa Cruz Mtns, California , 1989
67
Earthquake Effects - Fires
Loma Prieta, CA 1989
KGO-TV News ABC-7
68
Earthquake Effects - Tsunamis
1957 Aleutian Tsunami
Photograph Credit Henry Helbush. Source
National Geophysical Data Center
69
Earthquake Preparedness Before- develop a
disaster plan secure your home store flammable
pack survival kit lightly and conduct
earthquake drills.
70
Earthquake Preparedness
During- cover your head look for a safe place
to hide temporarily stay in an open area go to
a higher ground for tsunami alert and move away
from steep elevations.
71
Earthquake Preparedness
After- exit building calmly see if you have
injuries and do not enter a building in attempt
to save someone.
72
QUIZ
  • 1. Which activities are earthquakes usually
    associated with?
  • 2. What is a fault?
  • 3-5. Name the 3 movements of rock.
  • 6. What causes these movements? (2 words.)
  • 7. Which theory explains the cause why
    earthquakes occur?

73
QUIZ
  • 8-10. Name all types of faults.
  • 11. There are 3 types of focuses, the Shallow,
    _______, and the Deep.
  • 12. What is the slowest wave?
  • 13. Name the instrument that detects earthquakes
    and its recordings.
  • 14. At least how many circles are needed to
    locate the epicenter?

74
QUIZ
  • 15. Which wave can penetrate the cores?
  • 16. Which wave cannot penetrate the outer core?
  • 17. Who invented a scale used to describe an
    earthquake?
  • 18-19. Which main effects were described here?
  • 20. Name at least an engineering technique given.

75
Thank you for viewing and have a good day!
76
References
  • www.google.com
  • Integrated Science book

77
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78
QUIZ
  • Fill in the blanks
  • Earthquake is the the shaking or trembling caused
    by the sudden release of ________.
  • The point within Earth where faulting begins is
    the FOCUS, or ___________.
  • Shaking of earth due to movement of rocks along a
    _________.

79
QUIZ
  • 4. Can be visible on the ________ or can be far
    underground.
  • 5. ________ is where an oceanic plate is
    converging with a continental plate.
  • 6. San Andreas fault is what kind of fault?
  • 7. _______ results when a system of forces pushes
    an object from opposite sides.

80
QUIZ
  • 9. If the forces acting on these rocks exceed
    this limit, or overcome the ________ between
    blocks, the crust snaps and an earthquake occurs.
  • 10. One block can move down and the other can
    move up, or vice versa is a _______ fault.
  • 11. The point directly above the focus on the
    surface is the _________.

81
QUIZ
  • 12. ______ focus earthquake originates between
    the earths surface and a depth of 70 kilometers
    below the surface.
  • 13. _________ results when a system of forces is
    applied to an object in different directions.
  • 14. The exposed upward block forms a cliff-like
    feature known as a ______.

82
QUIZ
  • 15. In ______ focus , the earthquake originates
    between 70 and 300 kilometers beneath the surface.

83
answers
  • Fill in the blanks
  • Energy
  • Hypocenter
  • Fault
  • Crust
  • Subduction zone
  • Strike-slip
  • Compression

84
Answers
  • Fill in the blanks
  • 9. Friction
  • 10. Normal
  • 11. Epicenter
  • 12. Shallow
  • 13. Shearing
  • 14. Fault scarp
  • 15. Intermediate
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