11/18/15
 Earth’s
lithosphere is divided into
tectonic plates that move on top of
asthenosphere
 Theory
of plate tectonics explains:
• Continental drift
• Sea-floor spreading
Convection
• Hot material from
deep within Earth
rises while cooler
material near surface
sinks
• Motion of convecting
mantle drags plates
sideways
 Ridge
Push
• Occurs at mid-ocean
ridges
 Higher elevation than
surrounding lithosphere
• Gravity causes the
ridge to “push”
oceanic plate down
the lithosphereasthenosphere
boundary
 Slab
Pull
• Oceanic lithosphere
denser than
asthenosphere
• Oceanic plate sinks
and pulls rest of
tectonic plate with it
 Occurs because of
process of subduction
 Occurs
when two
plates push into one
another
 Three
types (depends
on plates involved)
• Continental/continental
• Continental/oceanic
• Oceanic/oceanic
 Occurs
when two
tectonic plates move
away from one
another
 Results
in new
oceanic lithosphere
(sea-floor spreading)
 Can
also be found on
continents
East African Rift
 Occurs
when two
tectonic plates slide
past each other
horizontally
 Plates
grind past one
another often
resulting in
earthquakes
• Tectonic plates are not
San Andreas Fault
smooth
 Movement
affected by:
• Type of plate
 Measure
motion by
use of GPS
• Shape of plate
• Interaction with
surrounding plates
 Generally
slow (few
centimeters per year)
• San Andreas fault is
exception
 “Stationary” GPS
satellites send
signals to ground
stations
• Amount of time taken
to receive signal in
relation to distance
determines rate