• Plate tectonics (pp 339-343)• Plate boundaries (pp 343-348)• Earthquakes (pp 375-384)

Wednesday July 11

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Free floating magnetite particles align following a well defined pattern around a magnet.If support is frozen, and magnet is moved, magnetite particles keep trace of the old position of the magnet

Magnetic poles drift?

Yes, but not possible to have two north poles!!!

Plate tectonics is the explanation!!

Evidences of plate tectonics

1) Shape of continents2) Magnetic pole drift3) Hot spots4) Magnetic striping and age of seabed5) Similarities in fauna and flora

Evidences of plate tectonics

1) Shape of continents2) Magnetic pole drift3) Hot spots4) Magnetic striping and age of seabed5) Similarities in fauna and flora

Evidences of plate tectonics

1) Shape of continents2) Magnetic pole drift3) Hot spots4) Magnetic striping and age of seabed5) Similarities in fauna and flora

Plate motion and

boundaries

Why do plates move??

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PLATE MOTIONThree types of plate boundary

Divergent boundary

Animation 1

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Example: Mid-Atlantic

Ridge •a topographically high area near the middle of the Atlantic Ocean

•splits nearly the entire Atlantic Ocean north to south,

Divergent: Atlantic Ridge

LAVA FOUNTAINSKRAFLA VOLCANOICELAND

Rio Grande Rift

Animation 2

Convergent boundary I:oceanic -continental plate involved ->

Subduction

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OCEANIC-CONTINENTAL COLLISONS SUSTAIN MOSTVOLCANIC ACTIVITY AROUND THE PACIFIC OCEAN

Convergent boundary II:oceanic -oceanic plates involved ->

SubductionSubduction processes in oceanic-oceanic plate convergence result in the formation of volcanic arc islands

Animation 3

Convergent boundary III:NO oceanic plate(s) involved -> Mountain

chains

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Convergent boundary III:NO oceanic plate(s) involved -> Mountain

chains

Example: Andes MtnsWest margin of the South American continent•oceanic Nazca Plate is pushed toward and beneath the continental portion of the South American Plate•typical example of a convergent plate boundary

Nazca - S.America plate collision

Transform boundary

Animation 4

Transform boundary

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Example:San Andreas fault in California

Pacific Plate slides past the North American Plate.

Transform boundary

Plate Motion Summary

Earthquakes

• Are due to the release of strain in the lithosphere

• They propagate as waves of two types:• Compression (or longitudinal or P-

mode) waves

• Deformation (or transversal or S-mode) waves