Earthquakes

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Earthquakes
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An Earthquake is the sudden movement of the earth

• It is caused by the abrupt release of strain that
  has accumulated over a long time

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Earthquakes in History
Horses killed by a collapsing wall - San
Francisco Earthquake 1906
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San Francisco - 1906
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Anchorage, Alaska - 1964
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Where Earthquakes Occur
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Where Earthquakes Occur

• Most Earthquakes occur at the boundaries where
  tectonic plates meet

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Where Earthquakes Occur
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How Earthquakes Happen

• The crust may first bend, and then when stress
  exceeds the strength of the rocks, break and
  snap to a new position.
• In the process, vibrations called seismic waves
  are generated.

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Seismic Waves
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Three Types of Faults
Strike-Slip
Thrust
Normal
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Strike-slip Fault Example
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Strike-slip Fault Example
1906 San Francisco Earthquake
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Normal Fault Example
Dixie Valley-Fairview Peaks, Nevada
earthquake December 16, 1954
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Thrust Fault Example
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Severity of an Earthquake

• The severity of an earthquake can be expressed in
  several ways

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Magnitude

• The measure of the amplitude of seismic waves
• Expressed by the Richter Scale

• Richter Earthquake Magnitudes Effects
• Less than 3.5 Generally not felt, but recorded.
• 3.5-5.4 Often felt, but rarely causes damage.
• Under 6.0 At most slight damage to well-designed
  buildings. Can cause major damage to poorly
  constructed buildings over small regions.
• 6.1-6.9 Can be destructive in areas up to about
  100 kilometers across where people live.
• 7.0-7.9 Major earthquake. Can cause serious
  damage over larger areas.
• 8 or greater Great earthquake. Can cause serious
  damage in areas several hundred kilometers
  across.

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Magnitude Richter Scale
Scale about 3.0
Scale about 6.0
Scale about 9.0
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Intensity

• A subjective measure that describes how strong a
  shock was felt at a particular location
• Expressed by the Modified Mercalli Scale

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What Controls the Level of Shaking?

• Magnitude
• More energy released
• Distance
• Shaking decays with distance
• Local soils
• amplify the shaking

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Earthquake Effects - Ground Shaking
Northridge, CA 1994
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Earthquake Effects - Ground Shaking
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Earthquake Effects - Ground Shaking
KGO-TV News ABC-7
Loma Prieta, CA 1989
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Earthquake Effects - Ground Shaking
Kobe, Japan 1995
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Earthquake Effects - Ground Shaking
Kobe, Japan 1995
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Earthquake Effects - Surface Faulting
Landers, CA 1992
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Earthquake Effects - Liquefaction
Source National Geophysical Data Center
Niigata, Japan 1964
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Earthquake Effects - Landslides
Turnnagin Heights,Alaska,1964
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Earthquake Effects - Fires
Loma Prieta, CA 1989
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Earthquake Effects - Tsunamis

• 1957 Aleutian Tsunami

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Earthquake Effects - Tsunamis
Sumatra Andaman Earthquake/Tsunami BEFORE
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Earthquake Effects - Tsunamis
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Earthquake Effects - Tsunamis
Sumatra Andaman Earthquake/Tsunami AFTER
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Earthquake Effects - Tsunamis
Sumatra Andaman Earthquake/Tsunami AFTER
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Pacific-North American Plate Boundary
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The San Andreas Fault
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Did You Feel It?
http//earthquake.usgs.gov