Chapter 16 Earthquakes

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Chapter 16Earthquakes
Photo credit USGS
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Causes of Earthquakes

• Types and Behavior of Seismic Waves
• Body Waves
• Primary or Compressional
• Secondary or Shear
• Surface Waves
• Raleigh (large vertical displacements)
• Love (shear)

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Elastic Rebound Theory
3 m offset
1906 San Francisco Earthquake
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Elastic Rebound Animation
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Offset Lettuce Rows - El Centro, CA
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Earthquake Focus and Hypocenter
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Earthquake Focus Animation
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Seismic Wave Types
Body Waves
Surface Waves
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equations for velocities
Vp k 4/3µ r
1/2
density
r
µ
shear modulus (rigidity)
Vs µ r
k
bulk modulus (rigidity)
1/2
because shear modulus (rigidity) for fluid is
zero,
S waves cannot propagate through a fluid
consequence of equations is that P waves are 1.7x
faster than S
can infer physical properties from P and S waves
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Wave Animations
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Locating and Measuring Earthquakes

• Determining the Location of an Earthquake
• Measuring the Size of an Earthquake
• Location and Size of Earthquakes in the United
  States

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Vertical Component Seismometer
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Horizontal Component Seismomter
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Seismograph Animation
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First Arrivals - Seismographic Records
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Distance - Time Relations
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P vs. S Wave Travel Time Curves
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Earthquake Location by Range
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Effects of Earthquakes

• Tsunamis
• World Distribution of Earthquakes
• First-Motion Studies of Earthquakes

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Modified Mercalli Intensity Index (1931)
1886 Charleston, SC earthquake
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Pancaked Building - 1985 Mexico City
Earthquakes dont kill people - buildings do!