Earthquakes

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Earthquakes

• Vibrations of the earths crust
• Occur when rocks shift suddenly under a fault
• When friction prevents rocks from moving the
  fault is said to be locked
• Rocks come under stress
• Friction over come
• Rocks grind past each other
• Slippage causes trembling earthquakes

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Elastic Rebound Theory

• Rocks on each side of the fault moving slowly
• If fault is locked stress on rocks increase
• Stressed past a certain point the rocks fracture
• Separate at weakest point
• Spring back to original shape or rebound
• As they fracture and slip they release energy in
  the form of vibrations called seismic waves
• Release of energy causes stress in other rocks
  causing them to fracture and spring back
  aftershocks

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Definitions

• Focus area of a fault where slippage first
  occurs
• Epicenter point on the earths surface directly
  above the focus

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Focus can be

• Shallow
• Within 70 km of the earths surface
• Most damage caused here
• Intermediate
• Occur at a depth of between 70 and 300 km
• Deep
• Between 33 and 650 km
•  
• By the time vibrations from intermediate focus or
  deep focus earthquake reach the surface, much of
  their energy has been used up. For this reason
  they do less damage
•  

5
Fun fact

• Earthquakes do not usually originate any deeper
  than 650 km because the high temperatures here
  cause rocks to act like plastics rather than
  fracturing.

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Earthquake zones

• Pacific Ring of Fire
• Large earthquake zone
• Includes the west coasts of North and South
  America, the east coast of Asia and the western
  pacific islands of the Philippines, Indonesia,
  New Guinea, and New Zealand.
• Some plates are being subducted
• Some plates are being scraped past each other
• Plate movements cause stress to build up in the
  rocks
• They fracture and shift

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Mid Ocean Ridge

• Oceanic crust pulling away from both sides of the
  ridge
• Causes stress in the rocks along the major ocean
  ridges
•  

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Eurasian- Mountain Belt

• Eurasian plate colliding with African and Indian
  plates
• Causes mountains and earthquakes
• What mountain range is this causing (Himalayans)

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Fault Zones

• Formed at plate boundaries because of intense
  stress when plates separate, collide, subduct or
  slide past each other
• Example San Andreas Fault Pacific plate slipping
  along North American plate
•  

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