Geol 456/656
The Plate Tectonics Paradigm
The key combination of ideas was the observation of oceanic transform
fault motions in agreement with the sea-floor spreading hypothesis.
Plate Margins
- Ocean Ridges - divergent, hot mantle upwelling where new
oceanic crust created, spreading usually perpendicular to ridge.
- Trenches - convergence by subduction of oceanic lithosphere,
rate comparable to ridge spreading, often oblique to trench; some
continent-continent collisions.
- Transform Faults - tangential motions, no crustal creation
or subduction.
Question: What was important about the focal mechanisms of earthquakes
on oceanic transform faults?
Plate Interiors
- Rigid, just transfer stress.
- No deformation, no earthquakes.
- Plate (lithosphere) only 80-150 km thick, 1000's of km wide.
Question: What does the apparent strength of thin plates suggest?
Question: How are different earthquake mechanisms distributed
in area? with depth?
