Earthquakes

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Earthquakes

• Haibei Luo
• Oct 17th,2005

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How earthquakes happen?

• An earthquake is the vibration,
  sometimes violent, of the Earth's surface that
  follows a release of energy in the Earth's crust.
  
• Many causes can result in the
  vibration of the Earths surface. Usually
  destructive quakes, however, are caused by
  dislocations of the crust.

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A cross section illustrating the main types of
plate boundaries. (Jose F. Vigil, the U.S.
Geological Survey, the Smithsonian Institution,
and the U.S. Naval Research Laboratory)
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Some terms

• focus the spot underground where the rock breaks
  in an earthquake.
• epicenter the place right above the focus (on
  top of the ground).
• seismic waves vibration in the process of
  breaking of the earths crust.
• Seismology The geophysical science of
  earthquakes and the mechanical properties of the
  earth.
• Seismograph an instrument that records the
  shaking of the earth's surface caused by seismic
  waves.

http//www.seinan-gu.ac.jp/djohnson/natural/focus
ep.html
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How seismologists measure earthquakes?

• The First Seismograph
  Modern Seismographs

Chang Heng's "earthquake weathercock" (From
Walker, 1982)
The basic seismograph (From Lutgens Tarbuck,
1989)
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What are earthquake hazards?
earthquake scenes Anchorage(1964),Japan(1993),
San Francisco(1906).
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• The Effect of Ground Shaking
• Ground Displacement
• Flooding
• Fire

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The great 1906 San Francisco earthquake and fire
destroyed most of the city and left 250,00 people
homeless. This photo show San Francisco was
burning after the 1906 earthquake. (From Shedlock
Pakiser, 1997)
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Measure earthquake magnitudes

• Most common one is Richter scale, invented
  by Charles F. Richter in 1934. The Richter
  magnitudes are based on a logarithmic scale (base
  10).

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Map of the Tectonic Plates
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Thank you!
An aerial view of the San Andreas fault in the
Carrizo Plain, Central California.