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EARTHQUAKES Chapter 12

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UNDER the lithosphere is the weak sphere, the putty-like plastic layer ... There can be friction along the fault jagged edges that snag the blocks of rock. ... – PowerPoint PPT presentation

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Title: EARTHQUAKES Chapter 12


1
EARTHQUAKESChapter 12
  • Section 1
  • How and Why Earthquakes Happen
  • Pages 295-300

2
REVIEW
  • LITHOSPHERE is the
  • the ROCKY outer layer of Earth including
  • the CRUST the rocky outer part of
  • the MANTLE
  • UNDER the lithosphere is the weak sphere, the
    putty-like plastic layer called the
  • ASTHENOSPHERE

3
NEED to KNOW from chapter 11
  • Lithosphere moves up and down depending on the
    balance of pressure between what is above,
    either ________ crust or ______ crust
  • CONTINENTAL
    OCEANIC
  • and what is below
  • the
    ASTHENOSPHERE

4
LITHOSPHERE MOVEMENT
  • Since the polar icecaps are melting due to golabl
    climate change, the ocean levels are rising
    making the ocean (lighter or heavier), so the
    lithosphere under the ocean will _____

  • SINK
  • Since the polar icecaps are melting, the ice on
    the land is decreasing making land (lighter or
    heavier), so the lithosphere under the land will
    ______

  • RISE

5
CAUSES of STRESS
  • As the lithosphere moves in this way, or as it
    moves as a result of tectonic plate movement it
    puts STRESS on rocks.
  • STRESS is a result of
  • FORCE exerted on rock.
  • STRESS is
  • the AMOUNT of FORCE exerted
  • on an area of rock.

6
CAUSES of STRESS
  • The types of tectonic plate movement that cause
    stress are
  • 1) CONVERGENCE which causes
  • COMPRESSION stress
  • 2) DIVERGENCE which causes
  • TENSION stress
  • 3) GRINDING/TRANSFORM which causes
  • SHEAR stress

7
RESULT of STRESS
  • Sometimes stress cause rock to DEFORM
  • DEFORMATION is when the crust
  • bends, tilts, or breaks
  • ch 11 deform.html

8
RESULT of STRESS
  • Sometimes stress cause rock to FOLD.
  • (Read about FOLDS in chapter 11 and take notes
    for extra credit.)

9
RESULT of STRESS
  • Sometimes stress causes rock to BREAK.
  • There are 2 kinds of breaks
  • Rock breaks ? broken pieces do NOT move
  • called a FRACTURE
  • 2) Rock breaks ? broken pieces DO MOVE
  • called a FAULT

10
FAULTS
  • The BIGGEST type of FAULT that we already studied
    are the CRACKS BETWEEN
  • TECTONIC PLATES which are called
  • BOUNDARIES
  • There are 3 types of boundaries
  • CONVERGENT
  • DIVERGENT
  • TRANSFORM

11
Chapter 12 EARTHQUAKES
  • An EARTHQUAKE is
  • MOVEMENTS OF THE GROUND CAUSED BY SUDDEN RELEASE
    OF ENERGY WHEN ROCKS ALONG A FAULT MOVE.
  • And a FAULT is
  • a CRACK between moving rocks!

12
WHY earthquakes do NOT happen
  • If the rocks along a fault are LOCKED then
    earthquakes do NOT happen!
  • A fault is LOCKED when
  • the ROCKS are PREVENTED from MOVING by
  • FRICTION

13
WHY earthquakes DO happen
  • If the rocks along a fault build up enough stress
    they suddenly grind past each other.
  • This sudden grinding slip is an earthquake.
  • "The ground seemed to twist under us like a top
    while it jerked this way and that, and up and
    down and every way," wrote a person describing
    the experience of being in the large 1906
    earthquake in San Francisco, CA.

14
WHY earthquakes DO happen
  • The expression on solid ground is often used to
    describe something as stable. Usually the solid
    ground underfoot seems very stable. But sometimes
    it is not.
  • EARTHQUAKES are defined as
  • MOVEMENTS OF THE GROUND THAT ARE CAUSED BY A
    SUDDEN RELEASE OF ENERGY WHEN ROCKS ALONG A FAULT
    MOVE.

15
WHY earthquakes DO happen
  • Geologists think earthquakes are a result of the
    rock which has been deformed by stress suddenly
    being able to return to its UNdeformed shape.
  • This springing back to previous shape is called
  • ELASTIC REBOUND

16
ANATOMY of an EARTHQUAKE
  • The location within the Earth along a fault where
    the first motion of an earthquake begins is
    called the
  • FOCUS or the HYPOCENTER
  • In addition to PAY ATTENTION CONCENTRATE, FOCUS
    means THE CENTRAL POINT, as in The FOCUS of
    this lesson is earthquakes.
  • HYPO means BELOW, so the hypocenter is the below
    ground center of the earthquake.

17
ANATOMY of an EARTHQUAKE
  • The point directly ABOVE the FOCUS, on the
    surface of the Earth, is called the
  • EPICENTER
  • EPI means OVER or UPON
  • (Your EPIdermis is the top layer of your
    dermis/skin)
  • So the EPIcenter is the point OVER the FOCUS of
    an earthquake thats UPON the Earths surface

18
This diagram shows an earthquake along a fault.
The focus of the earthquake is where the energy
is released underground. The epicenter is the
spot on the Earths surface directly above the
focus.
19
ANATOMY of an EARTHQUAKE
  • The FOCUS of an earthquake can be
  • SHALLOW, INTERMEDIATE, or DEEP
  • Which one causes the most damage?
  • SHALLOW
  • Why?
  • The energy of deeper earthquakes is spread out or
    dissipated as it moves to the surface.
  • The energy of a surface earthquake does not
    spread out or get used up moving TO the surface.
  • Its already HERE where we and our houses are!

20
The ENERGY from EARTHQUAKES
  • As rocks along a fault slip, they release energy
    in the form of vibrations called
  • SEISMIC WAVES
  • These waves ripple outward through the Earth from
    the focal point in a _________ pattern

  • CIRCULAR
  • as when you drop a stone in a pool.

21
This diagram shows an earthquake along a fault.
The focus of the earthquake is where the energy
is released underground. The epicenter is the
spot on the Earths surface directly above the
focus.
22
SEISMIC WAVES
  • There are 2 MAIN kinds of seismic waves
  • and each type has 2 subtypes
  • BODY waves include
  • either P waves or S waves
  • SURFACE waves include
  • either LOVE waves or RALEIGH
    waves

23
  • P waves
  • BODY WAVES
  • S waves
  • LOVE waves
  • SURFACE WAVES
  • RALEIGH waves

24
  • P waves primary , fast
  • BODY WAVES compression
    waves
  • S waves secondary / shear
  • second fastest
    side to side

25
(No Transcript)
26
  • LOVE waves slower but damaging
  • SURFACE WAVES sideways rocking
    motion
  • RALEIGH waves slower but damaging
  • ellipitical rolling motion

27
Love waves top / Raleigh waves bottom
28
SEISMIC WAVES EARTHS INTERIOR
  • The MORE DENSE the material they are passing
    through the (slower or faster) seismic waves
    move.
  • FASTER
  • Can you run faster on concrete or on sand?
  • CONCRETE is (more or less) dense than sand.
  • MORE
  • So, MORE DENSE FASTER

29
SEISMIC WAVES EARTHS INTERIOR
  • The waves that go THROUGH the CENTER of the Earth
    are the two types of _________ waves.

  • BODY
  • The 2 types of BODY waves are
  • S waves P
    waves

30
SEISMIC WAVES EARTHS INTERIOR
  • Can the BODY waves go through ALL the parts of
    Earths interior?
  • NO
  • They can NOT go through the
  • LIQUID
    __________ CORE

  • OUTER

31
SEISMIC WAVES EARTHS INTERIOR
  • Since BODY waves can NOT go through the liquid
    OUTER CORE there is a ______zone on the other
    side of the Earth that does NOT feel the waves.
  • SHADOW
    ZONE
  • YOUR shadow is a place where there is no _____
  • LIGHT
  • In the seismic shadow zone there are no _______
  • SEISMIC WAVES

32
Are faults always clean breaks?
  • Faults (do or do not) usually consist of a
    single, break.
  • do NOT
  • So, we refer to the complex network of cracks as
  • a FAULT ZONE

33
What are tectonic plates doing to cause
earthquakes?
  • -oceanic oceanic crust DIVERGE
  • -oceanic oceanic crust CONVERGE
  • -continental continental crust DIVERGE
  • -continental continental crust CONVERGE
  • -continental continental crust GRIND(transform)

34
Are earthquakes always on plate boundaries?
  • NO
  • Big earthquakes occurred in Missouri (1811
    1812).
  • Are the tectonic plates weve been studying
    converging, diverging, or transforming in
    Missouri?
  • NONE of these! So why the
    earthquakes?
  • An ancient fault (600 million years old) is
    buried beneath the rocks and sediment in
    Missouri.

35
ALWAYS on FAULTS?
  • While it is not as common, there are also some
    faults in the middle of plates. Movement along
    those faults can cause earthquakes too.
  • For example, many strong earthquakes shook the
    Mississippi River Valley between December 1811
    and March 1812.
  • Although this area is in the middle of the North
    American plate, there is a large fault. Its
    called the New Madrid Fault and movement along it
    caused the 1811-1812 earthquakes.

36
Animation Where do earthquakes happen?
  • http//www.windows.ucar.edu/tour/link/earth/geolo
    gy/quake_2.html

37
PREVIOUS EARTHQUAKES
  • The animation shows where earthquakes happened
    between 1960 and 1995. Each earthquake is shown
    on the map as a yellow dot. Did you see a pattern
    to where the dots are found?
  • Earthquakes do not happen at random locations.
    They are not equally spaced. Some areas have many
    earthquakes while other areas have few.
  • Since earthquakes happen along faults and most
    faults are near plate boundaries, the yellow dots
    in the animation are found mostly at the
    boundaries between Earths tectonic plates.

38
Where did earthquakes happen this week?
  • http//earthquake.usgs.gov/eqcenter/recenteqsww/Ma
    ps/region/N_America.php

39
REVIEW EARTHQUAKES
  • Earthquakes happen as large blocks of the Earths
    crust move suddenly past one another because of
    the force of plate tectonics. These blocks of the
    Earths crust meet at cracks called faults.
    Sometimes those pieces do not slide smoothly past
    one another.

40
REVIEW FAULTS
  • There can be friction along the fault jagged
    edges that snag the blocks of rock. This makes it
    difficult for them to move past each other.
  • Sometimes they get stuck together temporarily.

41
REVIEW FAULTS
  • a FAULT or FAULT LINE is
  • A BREAK IN A BODY OF ROCK ALONG WHICH THE ROCK ON
    ONE SIDE CAN MOVE WITH RESPECT TO THE ROCK ON THE
    OTHER SIDE.
  • A fault that runs along the boundary between two
    tectonic plates is called a
    transform fault.

42
REVIEW EARTHQUAKES
  • When the pieces of rock overcome the snags caused
    by friction, energy is released.
  • The release of energy causes shaking at the
    ground surface called an EARTHQUAKE.

43
How Where Earthquakes Happen
  • Each year, more than a million earthquakes occur
    worldwide. Most of these are so small that people
    do not feel the shaking. But some are large
    enough that people feel them, and a few of those
    are so large that they cause significant damage.

44
REVIEW FOCUS EPICENTER
  • The location inside the Earth where an earthquake
    begins is called the focus.
  • The point at the Earths surface directly above
    the focus is called the epicenter.
  • The strongest shaking happens at the epicenter.

45
REVIEW EARTHQUAKES
  • Earthquakes happen when rock below the Earths
    surface moves abruptly. Usually, the rock is
    moving along large cracks in Earths crust called
    faults. Most earthquakes happen at or near the
    boundaries between Earths tectonic plates
    because thats where there is usually a large
    concentration of faults. Some faults crack
    through the Earth because of the stress and
    strain of the moving plates. Other, large faults
    are at the boundary between plates, such as the
    San Andreas Fault on the North American west
    coast.

46
PREVIEW Section 3
  • Earthquakes can cause damage to things like
    buildings, bridges, and roads. Earthquakes can
    cause landslides and mudslides, too. If a large
    earthquake happens under the ocean it can cause a
    tsunami a giant ocean wave or series of waves.
  • Scientists can figure out whether an earthquake
    is likely to happen in a place by studying plate
    tectonics, the faults underground, and the
    history of the areas earthquakes. However,
    unlike weather events, earthquakes can not be
    forecast ahead of time.
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