StickSlip Activity Intro

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Stick-Slip Activity Intro

• Exploring an earthquake model

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What is Stick-Slip?

• The jerking motion that often occurs when two
  surfaces are sliding over each other.
  
• The surfaces alternate between sticking and
  slipping
  
• Common examples
• Music from a violin (bow across string)
• Sound of noisy brakes on a car
• Screeching car tires
• Glass Harp (wet finger around the rim of a wine
  glass)

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What is Required for Stick-Slip?

• The force required to un-stick the surfaces is
  greater than the force required to keep the
  surfaces moving.
  
• The static coefficient of friction must be higher
  than the kinetic coefficient of friction
  
• A force that varies with displacement is also
  required.
  
• An elastic (springy) material stores elastic
  energy as it deforms and could supply such a
  force.

Rigid materials are elastic to some degree even
rock!

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The Stick-Slip Cycle

• One cycle of stick-slip
• Surfaces are stuck
• An external shear force is applied
  (continuously)
  
• Elastic material deforms, storing elastic energy
• Surfaces remain stuck, since the force delivered
  to the contact area is less than the force needed
  to overcome static friction
  
• Eventually the force at the contact area
  overcomes static friction the surfaces begin to
  slide
  
• Stored energy in the elastic material is
  released, causing the surfaces to accelerate as
  they slide past each other
  
• As the elastic material returns to its previous
  shape (elastic rebound) the force delivered to
  the surfaces decreases until it can no longer
  overcome kinetic friction and the surfaces stop
  moving
• The surfaces are stuck again

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Stick-Slip on an Earthquake Fault
Stick
Slip
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Friction along fault segment
Deformed rocks store elastic potential energy
Elastic energy released! EARTHQUAKE!
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Earthquake Slip Activity

• Demo
• Workshop Activity

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Vocabulary

• Creep Slow, steady fault movement.
• Deformation The change in shape of an object as
  a result of the application of stress to it.
  
• Elasticity The property of returning to an
  initial form following deformation.
  
• Elastic rebound As plates move, elastic strain
  energy builds along edges, until rocks rupture
  and return to their undeformed shapes.
  
• Strain deformation of the earth.
• Static friction The force between two objects
  that are not moving relative to each other.
  Friction that keeps things from moving.
  
• Stress A force applied over an area.
• Stick-slip Adjacent surfaces alternating between
  sticking to each other and sliding past each
  other.