Living Things

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Earthquakes Comp. Sci. 2
7-1 Forces in Earths Crust 7-3 Monitoring
Earthquakes
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Vocabulary 7.1

• Stress
• Compression
• Shearing
• Normal Fault
• Reverse Fault
• Strike-slip Fault
• Plateau

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3 Kinds of Stress in Earths Crust pg. 223

• As Earths plates move, they can bend or fold
  rock. Forces created by movement of the Earths
  plates are examples of stress. Stress adds energy
  to rock until the rock changes shape or breaks.
• Three kinds of stress can occur in the Earths
  crust
• tension, compression, and shearing.
• All three work over millions of years to change
  the shape and volume of rock.
• Tension, compression, and shearing work over
  millions of years to change the shape and volume
  of rock

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How Does Stress Change Earths Crust? Pg. 223

• Tension-
• Tension is the stress force that pulls on the
  crust and thins the rock in the middle. It occurs
  where two plates pull apart.

1st kind of stress can occur in the crust.
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How Does Stress Change Earths Crust? Pg. 223

• Compression-
• Compression is the stress force that squeezes
  rock until it folds or breaks. It occurs where
  two plates come together and push against each
  other.

2nd kind of stress can occur in the crust.
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How Does Stress Change Earths Crust? Pg. 223

• Stress can push, pull, or squeeze rock in Earths
  crust.
• Shearing-Shearing is the stress force that pushes
  rock in two opposite directions. It occurs where
  two plates slip past each other.

3rd kind of stress can occur in the crust.
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Stress in Earths Crust Stress can push, pull, or
squeeze rock in Earths crust. Three kinds of
stress can occur in the crust. APPLY
CONCEPTS Look at the pair of arrows in the
second diagram. These arrows show how tension
affects rock. Draw a pair of arrows on the
third diagram to show how compression affects
rock. Then draw a pair of arrows on the bottom
diagram to show how shearing acts on rock
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Assess Your Understanding pg. 223

• I get it! Now I know that stress changes Earths
  crust by changing the ____________________________
  ________
• ________________________________________________

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How Do Faults Form? Pg. 224

• When enough stress builds up in rock, the rock
  breaks and makes a fault.
• The three main types of faults are
• normal faults
• reverse faults
• strike-slip faults

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How Do Faults Form?

• Normal Faults
• Normal faults form where rock is pulled apart by
  tension in Earths crust. The block above is
  angled fault called the hanging wall. The rock
  below the fault is called the footwall. The
  hanging wall slips downward when rock moves along
  the fault.
• Reverse Faults
• A reverse fault has the same structures as a
  normal fault, but the hanging wall moves up and
  the footwall moves down. Reverse faults form
  where compression pushes the rock of the crust
  together.
• Strike-Slip Faults
• Shearing produces strike-slip faults. The rocks
  on either side of a strike-slip fault slip past
  each other and have little up or down motion. A
  strike-slip fault that forms the boundary between
  two plates is called a transform boundary.

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Faults pgs. 224-225 The three main types of
faults are defined by the direction in which rock
moves along the fault.
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Apply It! Pg. 225

• The low angle of a thrust fault allows rock in
  the hanging wall to be pushed great distances.
  For example, over millions of years, rock along
  the Lewis thrust fault in Glacier National Park
  has moved 80 kilometers.
• Identify- Based on the arrows showing fault
  movements in the diagram, a thrust fault is a
  type of (normal fault, reverse fault).
• Challenge Why might the type of rock in the
  hanging wall of the Lewis thrust fault be
  different from the type of rock in the footwall?
• __________________________________________________
  __________________________________________________
  __________________________________________________
  __________________________________________________
  ____________________________________________

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Assess Your Understanding pg. 225

• 1a. Review When enough stress builds up in
  brittle rock, the rock breaks causing a
  ____________________.
• b. Infer- A geologist sees a fault along which
  blocks of rock in the footwall have moved higher
  relative to blocks of rock in the hanging wall.
  What type of fault is this?_______________________
  _______
• I got it! Now I know that faults form when
  ____________________
• __________________________________________________
  __________________________________________________
  __________________________________________________
  _____

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How Does Plate Movement Create New Landforms? Pg.
226

• Over millions of years, the forces of plate
  movement can change a flat plain into features
  such as anticlines and synclines, folded
  mountains, fault-block mountains, and plateaus.

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Folding pgs. 226-227

• Folding Earths Crust
• Folds are bends in rock that form when Earths
  crust is compressed and gets shorter and thicker.
  A fold in rock that bends upward into an arch is
  an anticline. A fold that bends downward in a V
  shape is a syncline.

Anticlines and Synclines Compression can cause
folds in the crust. Two types of folding are
anticlines, which arch up, and synclines, which
dip down.
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Fault Block Mountain

• Stretching Earths Crust
• Tension forces create normal faults where two
  plates move away from each other. A fault-block
  mountain forms when the hanging walls of two
  normal faults drop down on either side of the
  footwall.

Tension and Normal Faults As tension forces pull
the crust apart, two normal faults can form a
fault-block mountain range.
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Forces in Earths Crust Figure 2
Tension and Normal Faults As tension forces pull
the crust apart, two normal faults can form a
fault-block mountain range, as you can see in the
diagram. Predict Label the hanging wall and the
two footwalls in diagram A. in diagram B, draw
the new position of the hanging wall after
movement occurs. Describe what happens. __________
__________________________________________________
__________________________________________________
__________________________________________________
_____
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Plateau

• Uplifting Earths Crust
• Forces can also raise plateaus. A plateau is a
  large area of flat land that was lifted up high
  above sea level.

The Kaibab Plateau Look at the sequence of
drawings. In your own words, describe what
happens in the last two diagrams.
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Assess Your Understanding pg. 229

• 2a. Review- Normal Faults often occur when two
  plates (come together / putt apart)
• b. Interpret Diagrams Look at the diagram that
  accompanies the photograph in Figure 5. Does the
  block of rock in the middle move up as a result
  of movement along the normal faults? Explain.
• __________________________________________________
  __________________________________________________
  __________________________________________________
  __________________________________________________
  ________________________
• I get it! Now I know that plate movements create
  new features by
• __________________________________________________
  __________________________________________________
  __________________________________________________
  __________________________________________________
  ________________________

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• 7-2 Earthquakes and Seismic Waves

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Vocabulary 7.2

1. Earthquake
2. Focus
3. Epicenter
4. P wave
5. S wave
6. Surface wave
7. Seismograph
8. Modified Mercalli scale
9. Magnitude
10. Richter Scale
11. Moment magnitude scale

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Earthquakes and Seismic Waves

• Earthquakes start below the surface of the Earth.
  An earthquake's seismic waves carry energy up
  toward the surface and down through the interior.
• Seismic waves are vibrations that are similar to
  sound waves. They travel through Earth carrying
  energy released by an earthquake
• Look at the drawing showing Earths interior. At
  which point(s) can seismic waves be detected?
• A only
• A and B
• A, B, and C
• 2. Infer At which point do you think the
  seismic waves will have the most energy? Why?
• __________________________________________________
  __________________________________________________
  ____________________

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What Are Seismic Waves? Pg. 231

• Plate movement increases the stress along a fault
  until the rock slips or breaks and an earthquake
  begins. An earthquake is the shaking and
  trembling that happens when rock under Earths
  surface moves. The focus is the place under
  Earths surface where rock starts to move. The
  point on the surface directly above the focus is
  called the epicenter.
• Some of the energy released during
• an earthquake travels through Earth
• in the form of seismic waves. Seismic
• waves travel out in every direction
• from the focus.

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Types of Seismic Waves

• P Waves (A)
• The first waves to arrive, also known as primary
  waves. P waves compress and expand the ground
  like an accordion. P waves can damage buildings.
  P waves travel through solids and liquids.
• S Waves (B)
• After primary waves come secondary waves or S
  waves. S waves are seismic waves that can vibrate
  from side to side or up and down. Their
  vibrations are at an angle of 90 degrees to the
  direction that they travel. When S waves reach
  the surface, they shake structures violently. S
  waves cannot travel through liquids.
• Surface Waves (C)
• When P and S waves reach the surface, they become
  surface waves. Surface waves move more slowly
  than P and S waves but they can produce severe
  ground movements. Surface waves can make the
  ground roll like water waves in an almost
  circular pattern or shake buildings from side to
  side.

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Types of Seismic Waves pg. 233
P, S, and Surface Waves Earthquakes release
stored energy as seismic waves. Identify Draw
a line from each type of seismic wave to the
movement it causes.
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How Are Earthquakes Measured? Pg. 234
Modified Mercalli Scale The Modified Mercalli
scale uses Roman numerals to rate the damage and
shaking at any given location, usually close to
the earthquake.
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How Are Earthquakes Measured? Pg. 234
Earthquake Magnitude The table gives the moment
magnitudes of some recent earthquakes.
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Earthquakes and Seismic Waves pg. 236
Seismic Wave Speeds Seismographs at five
observation stations recorded the arrival times
of the P and S waves produced by an earthquake.
These data were used to draw the graph.
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Earthquakes and Seismic Waves pg. 237
An Earthquakes Epicenter The map shows how to
find the epicenter of an earthquake using data
from three seismographic stations.
Assess your Understanding
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Monitoring Earthquakes

• 7.3
• Vocabulary
• Seismogram

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Monitoring Earthquakes
Seismic Data From the USArray Project In 2004,
scientists in the USArray project placed 400
seismographs across the western United States.
Every month, 18 seismographs are picked up and
moved east, leapfrogging the other seismographs.
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Monitoring Earthquakes
Recording Seismic Waves In a simple seismograph,
a pen attached to a suspended weight records an
earthquakes seismic waves.
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Monitoring Earthquakes
Seismograms When an earthquakes seismic waves
reach a simple seismograph, the seismographs
drum vibrates. The vibrations are recorded by the
seismographs pen, producing a seismogram.
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Monitoring Earthquakes
Earthquake Risk The map shows areas where
serious earthquakes are likely to occur, based on
the location of past earthquakes across the
United States.
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Monitoring Earthquakes
Earthquakes Around the World Earthquakes are
closely linked to plate tectonics. The map shows
where past earthquakes have occurred in relation
to plate boundaries.