The surface of the Earth is cracked like a hard-boiled egg. Individual land masses, referred to as `Plates', are in constant motion relative to each other.
The word tectonic refers to motion, and indeed, where plates are moving against
each other, quite interesting things occur:
Mid-Ocean Ridges. (Divergent) Spreading centers where the mantle is up-welling. (Middle of Atlantic Ocean) |
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Subduction Zones or Trenches. Where oceanic crust is being lost. Occurs a little at a time, with sudden motions. (Nazca Plate into the S.A. plate) | Transform Faults. Where two plates are sliding against each other, though no crustal material is lost. (San Andreas Fault) |