Earthquakes

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Earthquakes
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What is an Earthquake?

• Earthquakethe vibration of Earth produced by the
  rapid release of energy
• Most often caused by slippage along a fault in
  Earths crust
• Focusthe zone within Earth where rock
  displacement produces an earthquake
• Produces waves that carry the energy throughout
  the Earth

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What is an Earthquake?

• Earthquakes and Faults
• A fault is a large fracture in Earths crust
• Most earthquakes occur along plate boundaries

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What is an Earthquake?

• Elastic Rebound
• 1906 San Francisco Earthquake
• San Andreas fault780 miles
• Boundary between the North American plate and the
  Pacific plate
• Pacific plate moved as much as 15 feet northward
  past the North American plate
• Sudden release of stored up energy in rocks that
  results in movement along a faultacts like a
  stretched rubber band

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What is an Earthquake?

• Fault creepslow, gradual displacement which
  occurs relatively smoothly
• Some segments regularly slip, producing small
  earthquakes
• Stick-slipremain locked and store elastic energy
  for a long time before releasing energy in a
  great earthquake
• Fault scarpcliff resulting from vertical
  displacement in which one side is lifted higher
  in relation to the other

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What is an Earthquake?

• Foreshocks
• Small earthquakes that precede a major earthquake
  by days or by several years
• Aftershocks
• Small earthquakes that are the result of
  adjustment of faults after a major earthquake

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Earthquake Waves

• Seismologystudy of earthquake waves
• Seismographsinstruments that record earthquake
  waves
• Seismogramsrecords from the seismographs

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Earthquake Waves

• Body waves
• P waves (primary waves)
• Push/pull
• Particles move in the same direction as the waves
• Longitudinal
• Change volume of intervening material
• S waves (secondary waves)
• Shake
• Particles move at right angles to the waves
• Transverse
• Change shape of the material that transmits them

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Earthquake Waves

• Surface waves
• Travel along the ground
• Moves ground like the ocean tosses a ship
• Up and down motion and side to side motion

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Finding Earthquake Epicenters

• Epicenterlocation on the surface of the Earth
  directly above the focus
• Scientists use triangulation to determine the
  epicenter
• Distance of the wave from three different seismic
  stations

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Earthquake Intensity and Magnitude

• Mercalli intensity scale
• Assesses damage
• Strength, distance from the epicenter, nature of
  surface materials, and building design
• Richter scale
• Measures magnitude
• Amplitude of the largest wave recorded on the
  seismogram
• Logarithmic scaletenfold increase for every
  number30 fold increase in magnitude