Earth Structure Basic layers Layered surface structure Spreading centers Subduction zones Hot Spots Transform faults Evidence Animations
Surface Layer Structure
All plate motions can be described by thinking about the movement of plates on a sphere.
Spreading Centers
Spreading centers form the longest mountain chain in the world, almost 60,000 km. They are areas of recently formed ocean crust, and have reasonable levels of shallow seismicity.
Subduction Zones
Note that Earth is density stratified, that is, each deeper layer is denser than the layer above. At the Peru-Chile Trench, the oceanic lithosphere is much denser than the continental lithosphere, so it sinks down into the mantle
Subduction zones are areas where plates collide, usually resulting in very deep earthquakes.
Ocean islands and basins can both be created and destroyed. Destruction occurs when two pieces of continental lithosphere or island arc collide: they accrete to each other and the basin between is destroyed. This process also brings old seafloor (ophiolites) up onto continent edges.
Hot Spots
Hot spots are areas of mantle “plumes” where hot material is rising to the surface from deep within the mantle. Plate movements over a hot spot form island chains, such as the Hawaiian Island- Emperor Seamount Chain in the Pacific Ocean.
Transform Faults
Transform faults form connections between spreading centers and subduction zones -- they are where plate boundaries are moving in opposite, but parallel directions.
Pacific NW has it all! 5 plates Subduction zones Spreading center (JdF Ridge) Transform faults Ophiolites (Olympics) Deep & shallow earthquakes Subduction volcanoes NEPTUNE - proposed regional cabled observatory - see
Plate Tectonics: Topography
Plate Tectonics: Volcanoes
Plate Tectonics: Earthquakes
Plate Tectonics: Seafloor Age
Magnetic anomalies remain from switch in magnetic polar direction over time...left distinct pattern on both seafloor and some rocks on continents.
The Integrated Picture
The breakup of Pangaea, a “Super Continent” is responsible for the current plate configuration.breakup
Plate Motions through time