EARTHQUAKES Chapter 12

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EARTHQUAKESChapter 12

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

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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

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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

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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

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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.

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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

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RESULT of STRESS

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

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RESULT of STRESS

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

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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

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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

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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!

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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

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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.

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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.

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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

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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.

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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

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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.
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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!

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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.

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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.
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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

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

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

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

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Love waves top / Raleigh waves bottom
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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

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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

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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

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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
  

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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

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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)

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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.

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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.

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Animation Where do earthquakes happen?

• http//www.windows.ucar.edu/tour/link/earth/geolo
  gy/quake_2.html

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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.

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Where did earthquakes happen this week?

• http//earthquake.usgs.gov/eqcenter/recenteqsww/Ma
  ps/region/N_America.php

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.