EARTHQUAKES

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EARTHQUAKES MOUNTAIN BUILDING

• FAULTS AND FOLDS

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FAULTS

• When STRESS is applied too quickly, or is too
  great, rocks will FAIL or BREAK
• The resulting fracture is referred to as a FAULT

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ANATOMY OF A FAULT

• In normal and reverse faults, your rock layers
  often break apart like this
• The HANGING wall is on top
• The FOOT wall is on bottom

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3 TYPES OF FAULTS

• NORMAL fault
• Fractures caused by horizontal TENSION
• The inconsistency you will find in the rock
  layers
• Much YOUNGER rock over OLDER rocks
• Occur along DIVERGENT plate boundaries

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A NORMAL FAULT CUTTING TUFF AND CONGLOMERATE IN
SHOSHONE, CALIFORNIA NEAR DEATH VALLEY

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TYPE TWO FAULT

• REVERSE fault
• Fractures that form as a result of horizontal
  COMPRESSION
• The inconsistency you will find in the rock
  layers
• Much OLDER rock over YOUNGER rocks
• Occur along CONVERGENT plate boundaries

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THRUSTED SEDIMENTARY ROCKS IN THE CANADIAN
ROCKIES. NOTE THE PERSON IN THE RED CIRCLE.
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TYPE THREE FAULT

• STRIKE-SLIP fault
• Fractures caused by horizontal SHEAR stress
• The inconsistency you will find in the rock
  layers
• Geologic features will SLIDE past one another
• Occurs along TRANSFORM plate boundaries

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STRIKE-SLIP FAULT CUTTING ACROSS A ROAD DISPLACES
THE LANE LINE
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LEFT-LATERAL SLIP
FAULT LINE
BEFORE
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RIGHT-LATERAL SLIP
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FOLDS!

• A planar feature, such as a bedding (rock) plane,
  that has been strongly WARPED, presumably by
  DEFORMATION
• In other words Layers of ROCK that have been
  subjected to large amounts of STRESS, which
  caused DUCTILE deformation i.e. permanent
  STRAIN

13
TYPE ONE FOLD

• ANTICLINE
• Folds that are shaped like As in their upright
  position
• Ages of the rock layers DECREASES from the INSIDE
  of the fold OUT

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TYPE TWO FOLD

• SYNCLINE
• Folds that are shaped like Us in their upright
  position
• Ages of the rock layers INCREASES from the INSIDE
  of the fold OUT

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ANATOMY OF A FOLD

• Axis the NOSE of the fold
• Axial plane The plane that cuts the fold in
  HALF.
• Each side of the plane is SYMMETRICAL
• Limb The ARMS of the fold

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ANTICLINE/SYNCLINE PAIRS

• An Anticline and Syncline who share LIMBS
• When you have a series of folds connected
  together, more often than not, you are seeing a
  collection of Anticline/Syncline pairs.

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LARGE-SCALE FOLDING OF THE APPALACHIANS IN
PENNSYLVANIA