Download plate tectonics brochure - University of Southern California

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
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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.