Download Earthquakes

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
Elastic Rebound Theory
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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
Definitions
• Focus: area of a fault where slippage first
occurs
• Epicenter: point on the earth’s surface directly
above the focus
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
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.
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
Mid Ocean Ridge
Oceanic crust pulling away from both sides of the
ridge
Causes stress in the rocks along the major ocean
ridges
Eurasian- Mountain Belt
– Eurasian plate colliding with African and Indian
plates
– Causes mountains and earthquakes
– What mountain range is this causing (Himalayans)
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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