What%20is%20the%20Elastic%20Rebound%20Theory?

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What is the Elastic Rebound Theory?

• Explains how energy is stored in rocks
• Rocks bend until the strength of the rock is
  exceeded
• Rupture occurs and the rocks quickly rebound to
  an undeformed shape
• Energy is released in waves that radiate outward
  from the fault

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• The Focus and Epicenter of an Earthquake

• The point within Earth where faulting begins is
  the focus, or hypocenter
• The point directly above the focus on the surface
  is the epicenter

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Where Do Earthquakes Occur and How Often?

• 80 of all earthquakes occur in the
  circum-Pacific belt
• most of these result from convergent margin
  activity
• 15 occur in the Mediterranean-Asiatic belt
• remaining 5 occur in the interiors of plates and
  on spreading ridge centers
• more than 150,000 quakes strong enough to be felt
  are recorded each year

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The Economics and Societal Impacts of EQs
Damage in Oakland, CA, 1989

• Building collapse
• Fire
• Tsunami
• Ground failure

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How is an Earthquakes Epicenter Located?

• Three seismograph stations are needed to locate
  the epicenter of an earthquake
• A circle where the radius equals the distance to
  the epicenter is drawn
• The intersection of the circles locates the
  epicenter

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Why do earthquakes occur?

• Fractures, faults
• Energy released
• and propagates in all directions as seismic
  waves causing
• earthquakes

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Crater Lake, Oregon
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The Stump of Mount Mazama
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Ash
What comes out of a volcano?
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Gas
What comes out of a volcano?
Most common H2O CO2 SO2 HCl
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What comes out of a volcano?
Lava
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Mauna Loa (Hawaii) A typical shield volcano
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Mt. St. Helens A typical composite volcano
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Mt. St. Helens after its 1980 eruption
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How Calderas Form
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Plate-tectonic setting of volcanism
Explosive (andesitic) volcanoes form at
subduction zones.
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Plate-tectonic setting of volcanism
At spreading centers, low pressure
triggers mantle meltingfluid basaltic magma
rises.
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Plate-tectonic setting of volcanism
Within plates, rising plumes of hotter mantle
feed hot spots varied volcanoes result (basaltic
on Hawaii).
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Mt. St. HelensPyroclasticEruption
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Mount Saint Helens- after
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Mt. Saint Helens before
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Phreatic (vapor) eruption
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Bulge
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After the eruption
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Pyroclastic eruption
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Volcanic landscape A Caldera (Crater Lake)