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Geology 112 - Earthquakes
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Activity #8 - Plate Tectonics and Earthquakes
Objective: Learning Outcome #1
Outline
Plate Tectonics
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• Evidence for plate tectonic theory
• Plates - Lithosphere and asthenosphere
• Plate boundaries
http://bingweb.binghamton.edu/~ajones/#Seismic%20Waves
Dynamic or Static?
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Internal Structure of the Earth
http://web.ics.purdue.edu/~braile/edumod/slinky/slinky.htm
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Some History
Fit of the Coastlines?
http://pubs.usgs.gov/gip/dynamic/dynamic.html
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Tectonics Links Together
Evidence Rocks, Fossils, and Sediments
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Continental Drift Hypothesis
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Continental Drift Hypothesis Breakup of Pangaea
"Scientists still do not appear to understand sufficiently that all earth sciences must contribute evidence toward unveiling the state of
our planet in earlier times, and that the truth of the matter can only be reached by combing all this evidence. . . It is only by combing
the information furnished by all the earth sciences that we can hope to determine 'truth' here, that is to say, to find the picture that sets
out all the known facts in the best arrangement and that therefore has the highest degree of probability. Further, we have to be
prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we
draw."
Alfred Wegener. The Origins of Continents and Oceans (4th edition)
Continents, Like a Ship, Sailing through Ocean Crust?
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The Seafloor
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Physical - Interior of Earth
Low Velocity Zone
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Depth
(km)
Increasing Seismic Velocity
• Decrease in rate of increase in seismic velocity
(especially S wave)
• Less Rigid “Squishy”
• 1% Molten
Seismic Velocities
Physical Layering
Lithosphere and Asthenosphere
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Oceanic vs. Continental Lithosphere
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• Lithosphere = Crust and uppermost mantle
• Strong lithosphere vs. weak asthenosphere
• Rigid lithosphere vs. “squishy” asthenosphere
• Elastic lithosphere vs. viscous asthenosphere
• Lithosphere is thin under oceans (5-100 km-thick)
• Thicker under continents (100-200 km-thick)
• Lithosphere is more rigid under oceans
Evidence - Mid-Ocean Ridge
Plate Boundaries
Science Channel - Bill Nye and Neil Driscoll
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http://youtu.be/6CsTTmvX6mc
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Evidence
Rock Samples from Mid-Ocean Ridge
• Volcanic rocks - Basalt
• Pillow-shaped - Underwater eruptions
http://www.whoi.edu/home/oceanus_images/pillow/
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Seafloor Spreading
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Evidence - Oceanic Crust Magnetism
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magnetic
Educational Multimedia Visualization Center of the Department of Earth Science, U.C.S.B
http://emvc.geol.ucsb.edu/index.htm
http://geology.uprm.edu/Morelock/1_image/magstr.jpg
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Magnetic Reversals and Seafloor Spreading
https://youtu.be/BCzCmldiaWQ
Educational Multimedia Visualization Center of the Department of Earth Science, U.C.S.B
http://emvc.geol.ucsb.edu/index.htm
Vine-Matthews Hypothesis
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Testing the Hypothesis by Deep Sea Drilling
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Harry Hess
Vine & Matthews
Educational Multimedia Visualization Center of the Department of Earth Science, U.C.S.B
http://emvc.geol.ucsb.edu/index.htm
Age of Oceanic Lithosphere
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Activity 8 Summary
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• Seismic Wave Propagation - Internal Structure of Earth
• Pangea and continental drift
• Evidence of plate tectonics
• Low Velocity Zone - Asthenosphere beneath lithosphere
• Difference between ocean and continental lithosphere
• Seafloor spreading and testing of Vine-Matthews
hypothesis
http://www.ngdc.noaa.gov/mgg/ocean_age/