Earthquake Movie Section 1: Earth s Crust in Motion How Do

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Earthquake Movie
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Section 1 Earths Crust in MotionHow Do Stress
Forces Affect Rock?

• The movement of earths plates creates powerful
  forces that squeeze or pull the rock in the crust
  these forces are examples of stress
• Stress a force that acts on rock to change its
  shape or volume
• An earthquake is the shaking and trembling that
  results from the movement of rock beneath earths
  surface

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How Does Stress Effect the Earths Crust?

• Deformation any change in the volume or shape
  or earths crust
• Three kinds of stress in the crust
• Shearing stress that pushes a mass of rock in
  two opposite directions
• Tension pulls on the crust, stretching rock so
  that it becomes thinner in the middle like warm
  bubble gum
• Compression squeezes rock until it folds or
  breaks like a giant trash compactor

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What Is a Fault?

• Fault a break in earths crust where slabs of
  crust slip past each other These usually occur
  at plate boundaries

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What Kind of Faults Are There?

• Three Kinds
• Strike-slip faults
• Normal Faults
• Reverse Faults

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What Are Strike-slip Faults?

• Strike-slip faults
• Shearing forces cause rocks to slip past each
  other sideways with little up and down Motion
• Ex. San Andreas fault in California

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What Are Normal Faults?

• Normal faults
• Tension forces cause the rocks to form the fault
  at an angle
• One block is above the fault
• Hanging wall the half of the fault that lies
  above
• Footwall the half of the fault that lies below
• Ex. Rio Grande rift valley

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What Are Reverse Faults?

• Reverse faults
• compression forces cause the rocks to move
  towards each other
• Same structure as normal fault but the blocks
  move in opposite direction hanging wall move up
• Ex. Appalachian Mountains and Mount Gould in
  Glacier National Park

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A miner walks on the foot wall and looks up at
the hanging wall!
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A
Hanging wall moves down
Hanging wall moves up
What type of fault?
What type of fault?
Normal Fault
Reverse Fault
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How Are Mountains Effected by These Forces?

• Fault-block mountains normal faults uplift a
  block of rock
• Folding bends in the rock that form when
  compression shortens and thickens part of the
  earths crust. Ex. Himalayas

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How Are Mountains Effected by These Forces?
(Continued)

• Anticlines a fold upward into an arch
• Syncline a fold downward into an arch
• Plateaus a large area of flat land elevated
  high above sea level

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Section 2 Measuring QuakesHow Does the Energy
of an Earthquake Travel Through Earth?

• Earthquakes most begin in the lithosphere
• Focus the point beneath the earths surface
  where rock that is under stress breaks,
  triggering an earthquake
• Epicenter the point on the earths surface
  directly above the focus

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What Are Seismic Waves?

• Seismic Waves vibrations that travel through
  Earth carrying the energy released during an
  earthquake
• They move like ripples on a pond
• They carry the energy of an earthquake away from
  the focus, through Earths interior, and across
  the surface
• The energy is greatest the the Epicenter

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What Are the Different Kinds of Seismic Waves?

• Three categories
• P waves
• S waves
• Surface waves
• P waves and S waves are sent out from the focus
  Surface waves develop when the waves reach the
  surface

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What Are P Waves?

• P waves are primary waves
• The first waves to arrive
• Earthquake waves that compress and expand the
  ground like an accordion
• Cause buildings to contract and expand

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What Are S Waves?

• S waves are secondary waves
• Earthquake waves that vibrate from side to side
  as well as up and down
• These waves shake the ground back and forth
• Shake structures violently
• Cannot move through liquids

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What Are Surface Waves?

• When P waves and S waves reach the surface some
  are transformed into surface waves
• Surface waves move more slowly than P waves and S
  waves
• Produce the most severe ground movements
• Can make the ground roll like ocean waves or
  shake buildings from side to side

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How Do Scientists Detect Seismic Waves?

• Seismograph records the ground movements caused
  by seismic waves as they move through the Earth

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How Do Scientists Measure Earthquakes?

• There are at least 20 different measures for
  rating earthquakes, three are
• Mercalli
• Richter
• Moment Magnitude
• Magnitude a measurement of earthquake strength
  based on seismic waves

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What Is the Mercalli Scale?

• Rated earthquakes according to their intensity
• Intensity strength of ground motion in a given
  place
• Not a precise measurement
• Describes how earthquakes affect people,
  buildings, and the land surface

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What Is the Richter Scale?

• A rating of the size of seismic waves as measured
  by a particular type of seismograph
• Accurate measurements for small, nearby
  earthquakes not large, distant earthquakes

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What Is the Moment Magnitude?

• A rating system that estimates the total energy
  released by an earthquake
• Can be used to rate earthquakes of all sizes,
  near or far
• Below 5.0 little damage
• Above 5.0 great destruction

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How Do Scientists Locate the Epicenter?

• Geologists use seismic waves
• P waves arrive first
• S waves arrive close behind
• Scientist measure the difference in arrival times
  
• The farther away an earthquake is the greater the
  time between their arrival
• Scientists draw three circles using data from
  seismographs set at different stations to see
  where they intersect the epicenter