Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Southern California Earthquake Center This brochure is designed to briefly explain the theory of plate tectonics and the effect plate tectonics has on the earthquake activity around the world, but specifically in California. For more information on earthquakes, please visit: www.scec.org www.usgs.gov Plate Tectonics The theory of plate tectonics defines how sections of the Earth’s crust are mobile. These sections are called plates. There are 14 major plates and they are classified as either continental, where they are composed mainly of land; or oceanic, where they are composed of the ocean. As the plates move, they collide along lines called Plate Boundaries. Continental-Continental Boundary A continental-continental boundary since the two plates have the same density, both plates get pushed up and create a mountain chain. One example of this boundary is the Himalayas in Asia. The Indian plate and Eurasian plate converge and lift. Convergent Boundaries Continental-Oceanic Boundary At a continental-oceanic boundary, the oceanic plate, because of its higher density, is thrusted underneath the continental plate. This is called subduction. A surface feature associated with subduction is a trench that forms at the boundary where subduction occurs. During subduction, as the crust subducts, it becomes hot, melts, and then the magma rises up to the surface and creates volcanoes. An example of subduction is the Cascadia subduction zone, which is a feature of the northern west coast of the U.S. At the Cascadia Subduction Zone, the Juan de Fuca plate, an oceanic plate, is subducting underneath the continental North American plate. This results in a mountain chain forming on the continental plate, and oftentimes these mountains are volcanic. Divergent Boundaries Divergent boundaries are where the two plates are moving in opposite directions. The surface feature associated with this is a ridge. As the plates part, the opening of the ridge allows magma to rise up and cool. This creates more of Earth’s crust. One example of divergent boundaries is the East Pacific Rise, which is what formed the Gulf of California and separated Baja California from the rest of the Mexican country. Oceanic-Oceanic Boundary An oceanic-oceanic boundary is treated a lot like oceanic-continental, because the older, denser plate subducts under the younger, less dense plate and a trench is formed. An example of this boundary is associated with the creation of the Solomon Islands in the South Pacific. http://slohs.slcusd.org/pages/teachers/rhamley/Plate%20Tecton ics/transform.jpeg http://2.bp.blogspot.com/_oWvK6SEOBY/SQrzqsVLwqI/AAAAAAAAAGA/KSYBDOafn2Y/s 320/divergent+bounary.jpg http://en.wikipedia.org/wiki/Convergent boundary Transform Boundaries Transform boundaries are where two plates slide past each other in a parallel fashion. The surface feature that defines this is apparent offset of rivers, roads, landmarks, etc… At transform boundaries, Earth’s crust neither created, nor destroyed. An example of this is the San Andreas fault in California. Here, the Pacific plate and North American plate slide past each other.