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Earthquake Movie. Section 1: Earth’s Crust in Motion How Do Stress Forces Affect Rock?. The movement of earth’s 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

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section 1 earth s crust in motion how do stress forces affect rock
Section 1: Earth’s Crust in MotionHow Do Stress Forces Affect Rock?
  • The movement of earth’s platescreates 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 earth’s surface
how does stress effect the earth s crust
How Does Stress Effect the Earth’s Crust?
  • Deformation – any change in the volume or shape or earth’s 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
what is a fault
What Is a Fault?
  • Fault – a break in earth’s crust where slabs of crust slip past each other; These usually occur at plate boundaries
what kind of faults are there
What Kind of Faults Are There?
  • Three Kinds:
    • Strike-slip faults
    • Normal Faults
    • Reverse Faults
what are strike slip faults
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
what are normal faults
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
what are reverse faults
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

A miner walks on the foot wall and looks up at the hanging wall!



Hanging wall moves down

Hanging wall moves up

What type of fault?

What type of fault?

Normal Fault

Reverse Fault

how are mountains effected by these forces
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 earth’s crust. Ex. Himalayas
how are mountains effected by these forces continued
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
section 2 measuring quakes how does the energy of an earthquake travel through earth
Section 2: Measuring QuakesHow Does the Energy of an Earthquake Travel Through Earth?
  • Earthquakes – most begin in the lithosphere
  • Focus – the point beneath the earth’s surface where rock that is under stress breaks, triggering an earthquake
  • Epicenter – the point on the earth’s surface directly above the focus
what are seismic waves
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 Earth’s interior, and across the surface
    • The energy is greatest the theEpicenter
what are the different kinds of seismic waves
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
what are p waves
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
what are s waves
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
what are surface waves
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
how do scientists detect seismic waves
How Do Scientists Detect Seismic Waves?
  • Seismograph – records the ground movements caused by seismic waves as they move through the Earth
how do scientists measure earthquakes
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
what is the mercalli scale
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
what is the richter scale
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
what is the moment magnitude
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
how do scientists locate the epicenter
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