Plate Boundaries: Convergent, Divergent, Transform

1min 25s Novice

What are the major plate tectonic boundaries?

Video lecture on divergent, transform, and convergent types of plate boundaries. Recorded during a 2007 teacher workshop on earthquakes and tectonics. Speaker is Dr. Robert Butler, University of Portland Oregon

Three main types of plate boundaries:

  • Divergent: extensional; the plates move apart. Spreading ridges, basin-range
  • Convergent: compressional; plates move toward each other. Includes: Subduction zones and mountain building.
  • Transform: shearing; plates slide past each other. Strike-slip motion.

Keypoints:

Discovery

  • Where do the most earthquakes occur worldwide?
  • Where do most volcanoes occur?
  • What do the concentrations of earthquakes tell us about plate interaction?
  • Does the location of earthquakes and volcanoes show a pattern? If so, what tectonic process may be responsible? (compression, extension, shearing)

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The subduction zone iswhere two tectonic (lithospheric) plates come together, one subducting (diving) beneath the other. The plates are locked together and periodically overcome the friction causing the leading edge of the overlying plate to surge back, lifting a wall of water producting a tsunami.

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A transform fault is a type of strike-slip fault wherein the relative horizontal slip is accommodating the movement between two ocean ridges or other tectonic boundaries. They are connected on both ends to other faults.

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In a normal fault, the block above the fault moves down relative to the block below the fault. This fault motion is caused by extensional forces and results in extension. Other names: normal-slip fault, tensional fault or gravity fault. Examples: Sierra Nevada/Owens Valley; Basin & Range faults.

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In a reverse fault, the block above the fault moves up relative to the block below the fault. This fault motion is caused by compressional forces and results in shortening. A reverse fault is called a thrust fault if the dip of the fault plane is small. Other names: thrust fault, reverse-slip fault or compressional fault]. Examples: Rocky Mountains, Himalayas.

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In a strike-slip fault, the movement of blocks along a fault is horizontal. The fault motion of a strike-slip fault is caused by shearing forces. Other names: transcurrent fault, lateral fault, tear fault or wrench fault. Examples: San Andreas Fault, California; Anatolian Fault, Turkey.

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