Chapter 2 Forces in the Earth

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Chapter 2Forces in the Earth

• Section 2-1
• What Causes Earthquakes?

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I. Pressure (in Earth)

• Pressure Force acting on an area.
• Pressure is released as a result of earthquakes.
• Pressure builds up from the force of rocks
  underground.
• Bending and stretching apply pressure to the
  rocks.

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E. Elastic Limit limit to how much pressure an
object can withstand and still return to its
original shape

• When the elastic limit is passed, the item
  remains out of shape or breaks.
• Rubber band
• Balloon

http//www.learner.org/jnorth/images/graphics/m/Mu
scle_RubberBand2.jpg
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II. Pressure in rock layers

• Rocks also have an elastic limit
• They will fold or break
• Earthquake vibrations caused when rocks break

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III. Finding Fault

• Fault
• When rocks break under pressure, they move
• A fracture within the earth where rock movement
  occurs (blue card definition)
• Locations
• Can be near the surface
• Can be deep beneath earths surface

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C. Causes/Types of Forces

• Compression
• Push rocks together

http//www.myndeye.com/earthquakes/thrustanimation
.gif
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• Tension
• Pull rocks apart

http//www.dsuper.net/innotech/quake/NormalAnimat
ion1.gif
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• Shearing
• Causes rocks to slide past each other

http//www.dsuper.net/innotech/quake/strikeanimat
ion2.gif
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D. Types of Faults

• Normal Fault
• Caused by tension forces
• The rock above moves downward
• Can form mountains
• Sierra Nevada Mountains in California

http//www.scetv.org/education/ntti/images/2003/st
ressed/stressed1.gif
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http//www-tc.pbs.org/weta/thewest/places/states/c
alifornia/ca_sierra.jpg
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• Reverse Fault
• Caused by compression forces breaking rock
• The rock above the fault moves upward
• Ex mountains that are part of the Himalayas
  separating India and China

http//www.scetv.org/education/ntti/images/2003/st
ressed/stressed2.gif
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http//static.howstuffworks.com/gif/willow/the-him
alayas0.gif
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http//michaelgreenwell.files.wordpress.com/2007/0
7/himalayas.jpg
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• Strike-Slip Fault
• Caused by shearing forces
• movement is usually short and sudden, but can be
  slow and steady
• Ex San Andreas Fault

http//www.scetv.org/education/ntti/images/2003/st
ressed/stressed3.gif
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http//geology.com/articles/images/san-andreas-fau
lt-map.jpg