GPS Measures Deformation in Subduction Zones: Ocean/continent

How Does Land Jump in an Earthquake?

This animation shows that GPS can record the movement of the leading edge of the overlying continental plate in a subduction zone. The plates are locked and the overlying plate is forced back. When friction is overcome and strain is released, the GPS receiver will snap back toward its original position. This animation is exaggerated to depict the relative motion of plates and GPS as seen in the 2010 Magnitude 8.8 earthquake in Chile where the land in places rebounded 10 meters.


Keypoints:

  • Modern GPS measure incremental movement of Earth's surface
  • In a subduction zone plates are locked together
  • The overlying plate is pushed back due to friction, deforming & building stress
  • When stress is overcome, a megathrust earthquake occurs
  • Megathrust earthquakes commonly produce tsunamis

Total Time: 49s
Level: Novice

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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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Native American oral history, tsunami geology along the Pacific Northwest coastlines, dating of "Ghost Forests", and Sumurai records indicate that a Great magnitude 9 earthquake occurred off the coast of Oregon and Washington on January 26, 1700 at 9:00 pm. This was pre-European contact.

Animation Novice

 GPS records the movement of the leading edge of the overlying continental plate in a subduction zone. The plates are locked and the overlying plate is forced back. When friction is overcome and strain is released, the GPS receiver will snap back toward its original position. 

Animation Novice

Subduction zones show that there are 3 distinct areas of movement in the overlying plate:

  1. constant movement above the locked leading edge,
  2. see-saw pattern of back-&-forth movement above a zone that alternately locks then slips, and
  3. no movement far inland above the deeper part of the diving oceanic plate.
Animation Novice

Subduction-zone megathrust earthquakes, the most powerful earthquakes in the world, can produce tsunamis through a variety of structures that are missed by simple models including: fault boundary rupture, deformation of overlying plate, splay faults and landslides. From a hazards viewpoint, it is critical to remember that tsunamis are multiple waves that often arrive on shore for many hours after the initial wave.

Animation Novice