Convection is like a boiling pot. Heated soup rises to the surface, spreads and begins to cool, and then sinks back to the bottom of the pot where it is reheated and rises again. Plate tectonics • Plates are driven by cooling of Earth (convection) • Gravity provides additional force to move plates. Modified from USGS Graphics ? ? ?
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Convection is like a boiling pot. Heated soup rises to the surface, spreads and begins to cool, and then sinks back to the bottom of the pot where it is reheated and rises again.
Plate tectonics• Plates are driven by cooling of Earth (convection) • Gravity provides additional force to move plates.
Modified from USGS Graphics
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What are the tectonic plates?
AKA: Lithospheric plate• The ~100-km-thick surface of the Earth;• Contains crust and part of the upper mantle;• It is rigid and brittle;• Fractures to produce earthquakes.
What is the asthenosphere?
Asthenosphere:• Is the hotter upper mantle below the lithospheric
plate;• Can flow like silly putty; and• Is a viscoelastic solid, NOT liquid!!
US
GS
Gra
phic
s
Three Basic Types of Plate BoundariesDivergent
ConvergentTransform
USGS Graphics
Using hands to show relative motion
Three Basic Types of Plate BoundariesDivergent
ConvergentTransform
USGS Graphics
There are a dozen large lithospheric plates (smaller plates not shown).Some plates have continents; some don’t. All are in motion.
Question: What evidence is there for these plate boundaries?
Tectonic Plates
There are thousands of small earthquakes every day “Strong” earthquakes (~M7) occur once a month. >M8 occur about once/year.
Earthquakes
Where are the deepest earthquakes?
For earthquakes of the past 2 weeks, go to http://www.iris.edu/seismon/
Note on Source: First 8 slides are modified from a slide show prepared by Dr. Robert Note on Source: First 8 slides are modified from a slide show prepared by Dr. Robert Butler, University of Portland, and Jenda Johnson,Butler, University of Portland, and Jenda Johnson,……the full source of which can be found at:the full source of which can be found at: