M 7'8 Earthquake Near Colima, Mexico

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M 7.8 Earthquake Near Colima, Mexico

• Wednesday, January 22, 2003 at 20635
• Shallow earthquake occurred in a seismically
  active zone
• Occurred near the juncture of three tectonic
  plates
• Killed 23 people

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Are These Earthquakes Common?
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Data from the Earthquake

• Seismograms record ground shaking
• Record of displacement as a function of time
• Tell us all we know about earthquakes

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Plate Tectonics

• Physical Geology 3101

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Continental Drift theory

• Fit of the continents
• Apparent magnetic polar wandering
• Unique rocks match (coal, glaciers...),
• Unique fossils match,
• Problem how did the continents drift?

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Sea Floor Spreading

• Pairs of magnetically reversed stripes on the
  floor of the ocean.
• The oceans are much younger than the continents
• The sea floors get younger toward the mid oceanic
  ridges.

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Plate Margins

• Lithospheric plates, 100 km thick
• Geologic activity at margins
• divergent,
• convergent
• transform

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Divergent boundaries plates move away from each
other

• A. Mid-ocean ridge spreading centers
• 1. Create new oceanic lithosphere
• 2. Gentle, basalt lava volcanoes
• 3. Shallow (lt10km) small/med. earthquakes
• 4. Iceland, mid-Atlantic Ridge
• B. Continental rift
• 1. Tears continent in two to create an ocean
• 2. Rio Grande Rift, East Africa

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Divergent Boundary
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Convergent margins

• Subduction Zones
• Oceanic-Oceanic
• Oceanic-Continental
• Collisions
• Continent-Continent boundaries

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Subduction Zones

• Destroys ocean lithosphere, ocean plate subducted
  under other plate and melts
• Explosive volcanoes
• Island arc (Philippines, Aleutians)
• Volcanic arc (Andes, S. Mexico)
• Huge deep earthquakes (lt700km),

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Parts of subduction zones

• Trench
• Subduction complex
• Volcanic arcs
• Back-arc basin

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Oceanic-Oceanic
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Convergent Boundary
Ocean-Continent
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Oceanic-Continental
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Continent-Continent

• Huge mountains
• No volcanoes
• Lots of earthquakes
• Folded rocks, continents are joined together
• Himalayas, Alps

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Continent Collision
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Convergent Boundary
Continent-Continent
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Transform plate margins plates slide past each
other, side-by-side

• No volcanoes
• Earthquakes with variable depths
• San Andreas Fault

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Oceanic Transform
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Transform Boundary
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Hot spots

• Plumes of hot material from the mantle
• Can show the absolute rate of plate movement.

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Most geologists believe that convection drives
plate tectonics.

• Thermal convection cell

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Group Exercise

• COOPERATIVE - One set of answers from the group,
  everyone has to agree
• CRITERIA FOR SUCCESS -- Everyone must be able to
  explain the procedure used to solve the problem.
• INDIVIDUAL ACCOUNTABILITY -- Random selection to
  give answers.
• EXPECTED BEHAVIORS -- Everyone should
  participate, encourage each other
• PROCESSING -- List three things you did well as a
  group. List one thing you can do better tomorrow.

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Question

• What is a tectonic plate?
• What are the type of plate boundaries?
• Define all sub-types boundaries
• What plate to we live on?
• What where the key observations that were used to
  come up the the theory of plate tectonics?
• What drives the plates?