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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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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