Natural Disasters and Plate Tectonics

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Natural Disasters and Plate Tectonics

• To experience the drama of plate tectonics --
  the jostling of the giant plates that carry
  continents and oceans -- try this experiment Sit
  in a comfortable chair, hold your hand out, and
  watch your fingernails grow. That's about the
  average speed of a tectonic plate. But wait
  around long enough, and even the tortoise crawl
  of plate tectonics will have dramatic and deadly
  consequences.
• www.pbs.org/wnet/savageearth/earthquakes/index.htm
  l

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Minor Quakes Happen All the Time

• If you imagine the Earth as a giant bell, it's
  ringing with earthquakes every second of the day
  -- from the many imperceptible clinks of
  microquakes to the deafening gong of very
  occasional but "great" earthquakes (those of
  magnitude 8.0 or greater).

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Daily Quakes

• The U.S. Geological Survey estimates that several
  million tremblers, most undetectable, happen
  every day.

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Where Earthquakes Occur

• Most earthquakes happen near the boundaries of
  tectonic plates.
• They can happen at areas where plates diverge, at
  areas where plates converge and at areas where
  plates transform.
• Earthquakes can also happen in the stable
  interior of continents.
• http//www.pbs.org/wnet/savageearth/animations/ear
  thquakes/index.html

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What Causes Earthquakes

• Earthquakes appear at fault lines.
• A fault is a fracture or a bunch of fractures
  between two blocks of rock.
• Faults allow the blocks to move relative to each
  other.
• http//www.pbs.org/wnet/savageearth/earthquakes/in
  dex.html
• Strike-Slip Fault

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What Happens at Faults

• Faults are usually stuck or locked.
• This causes stress to build up as the plates move
  past each other.
• A tremendous amount of stored energy builds up in
  the plates as they slowly creep past each other.
• When the plates finally slip, all this energy
  gets released.

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Seismic Waves

• When the energy gets released it is like a very
  tightly wound spring uncoiling.
• The uncoiling spring causes a seismic (means
  shaking) wave through the rock.
• That is what causes the earthquakes.

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Body Waves

• Earthquakes begin at the focus.
• There are two main kinds of seismic waves body
  waves and surface waves.
• Body waves travel outward in all directions from
  the quakes focus.
• Body waves can be further divided into
• Primary (P)-Waves
• Secondary (S)-Waves

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P-Waves and S-Waves

• P-Waves and S-Waves are both body waves.
• The P-Wave is the primary wave. These hit first.
• Often you will hear a sound like a train.
• The S-Wave will come as a sudden powerful jolt.
• http//www.pbs.org/wnet/savageearth/earthquakes/in
  dex.html

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Surface Waves

• Surface waves only occur in the upper few hundred
  miles of the crust.
• They travel parallel to the surface, like ripples
  on the surface of a pond.
• They are also slower than body waves.

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Surface Waves

• These follow the body waves and come as an up and
  down and back and forth motion.
• Surface waves make the ground appear to roll like
  the surface of the ocean.
• This is what topples buildings and destroys
  cities. http//www.pbs.org/wnet/savageearth/animat
  ions/wave-surface.html

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Seismologists

• People who study earthquakes are called
  seismologists.
• The best know scale for measuring an earthquake
  is the Richter scale.

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Richter Scale

• Each 1 point increase up the scale equals an
  earthquake ten times stronger.
• Therefore a six is ten times stronger than a
  five.
• How much stronger is a six earthquake than a four
  earthquake?
• http//www.pbs.org/wnet/savageearth/earthquakes/in
  dex.html

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Epicenter

• The strongest shaking occurs at the epicenter.
• The epicenter is the point on the surface
  directly above the focus of the earthquake.

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Liquefaction

• Another hazard is liquefaction.
• Liquefaction happens when loose, moist soil or
  sand is shaken so hard that individual grains
  separate.
• The earth is turned into a soft, fluid slurry
  that can swallow entire buildings.

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Liquefaction
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Earthquake Prediction

• It is very difficult to accurately predict an
  earthquake is coming as the following link shows.
• http//www.teachersdomain.org/resources/ess05/sci/
  ess/earthsys/japan/index.html

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San Francisco 1906
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San Andreas Fault

• The San Andreas fault, in California, occurs
  where the North American plate and the Pacific
  plate slide past each other.
• Its actually the largest of a bunch of faults
  connecting these two plates!
• http//www.exploratorium.edu/faultline/project/sta
  rt.html

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Earthquake Video

• Earth Science Earthquakes

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(No Transcript)
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Ring of Fire

• Alaska's frigid and remote Aleutian island chain
• The Andes mountains of South America
• http//www.pbs.org/wnet/savageearth/hellscrust/htm
  l/sidebar3.html

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• The tropical islands of Micronesia would seem to
  have little in common.

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Most Active Place on Earth

• The ring of fire is the most volcanically and
  seismically active region on Earth.
• Three-fourths of Earth's active and dormant
  volcanoes -- including Mount St. Helens.
• This is a subduction zone.

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Pacific Plate

• The ring of fire is where the Pacific and other
  oceanic plates subduct beneath bordering
  continents.
• In South America, the Nazca oceanic plate
  subducts beneath the South American plate,
  pushing up the Andes mountains.

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Mount Saint Helens

• In the Pacific Northwest (Portland, Washington
  area)
• The Juan de Fuca plate, subducts beneath the
  North American plate causing Earthquakes and
  volcanoes.
• The mountains of this region include the cascades
  where Mount Saint Helens is located.
• http//www.teachersdomain.org/resources/ess05/sci/
  ess/earthsys/helens/index.html
• http//video.google.com/videoplay?docid3977416382
  972126736

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Aleutian Islands

• Volcanic Mountains
• Formed by the subduction of the Pacific plate
  beneath the North American plate.

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Russia and Japan

• The ring of fire then heads through Russia and
  Japan.
• Here the Pacific Plate subducts beneath the
  Eurasian plate.
• This is how Mount Fuji is formed.

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Micronesia and New Guinea

• The last section of the Ring of Fire is made up
  of Micronesia (Philippines, Indonesia) and New
  Guinea.
• Here the Indo-Australian plate subducts below the
  Pacific.
• In New Zealand the Pacific plate subducts below
  the Indo-Australian.

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Citations

• http//www.pbs.org/wnet/savageearth/animations/wav
  e-surface.html
• Earth Science Earthquakes
• Volcanoes Mountains of Fire