Plate Tectonics Notes # 2
Tsunamis: means “ wave in the harbor”
in Japanese. When there is an
earthquake underwater, the sea floor
may drop down suddenly due to
. FAULTING
The result is a wave
that can reach 100 feet
(30 Meters)
or more in height. As the approaching
tsunami rises up in the water , it pulls
the water near the shore with it, sort of
like lifting a flat bag off the ground. As
you lift higher, the edges of the bag
move towards where you are lifting.
FAULTING
Zones of Earth- pg. 10 ESRT!
Discontinuity
Discontinuity : a place located at the
boundaries between the CRUST and
OUTER CORE
mantle, the mantle and
,
and outer core and INNER CORE
where the density of the rocks increases
dramatically (as you move inwards) . We
have located these discontinuities by
studying seismic wave PATTERNS , and
refraction/reflection of the waves at these
boundaries. THIS IS HOW WE KNOW
WHAT THE LAYERS OF THE EARTH ARE!
Examples of a discontinuity…
CRUST
The crust is the outermost
part of the earth below the
atmosphere or
hydrosphere. Composed
or made up of mostly solid
ROCKS including all the
soil and weathered and
eroded rock.
- The crust is solid, cold, and
brittle ( breaks easily).
MANTLE
Mantle: the mantle is below the crust. The
thickest zone that contains approximately
80% of Earth’s volume. The mantle is
divided into three different layers.



Rigid Mantle
Asthenosphere
Stiffer Mantle
RIGID MANTLE
RIGID MANTLE: this is part of the mantle
that is similar to the solid rocks in the
crust. Due to this fact it travels around
when the plates move with the
CRUST
__________.
The crust and this rigid part
of the mantle are collectively called the
lithosphere. In between the crust and the
rigid mantle is a region called the MOHO.
This represents a boundary where the
rocks _______________
rapidly in
INCREASE
density. Even though there are density
differences the crust and mantle are
considered a single part (THE
LITHOSPHERE) and move together!
Asthenosphere (Plastic Mantle)
ASTHENOSPHERE (PLASTIC MANTLE)- called
the plastic mantle because it behaves and flows
like silly putty , bread dough, or
HONEY .
This zone was discovered because it was found
that seismic waves decrease in velocity from
100km to 700km below the Earth’s surface.
(Seismic waves travel more slowly through liquids
than solids). It is a plastic-like portion of the upper
mantle that is partly MELTED . SEE ESRT
PG 10! The TEMPERATURE of the
asthenosphere is above the melting point
indicating that it is melted. Due to its “plasticky”
nature, the ASTHENOSPHERE allows the
plates of the lithosphere to float around, move,
pull apart, or CRASH
into each other.
Stiffer Mantle
Stiffer Mantle: this part is solid again until
you get to the ………………..
Outer Core
OUTER CORE- it is a
LIQUID
__________
and we know
S
this because NO ___waves will pass through it!
There is also a major drop
in P-wave velocity
indicating that the wave has
moved from a
SOLID
_________(medium
mantle) to a
LIQUID
___________medium
(outer core).
Inner Core
INNER CORE: very dense
SOLID
_____________
composed of nickel
and iron also. Believed to be a solid
due to the observation that P-wave
INCREASES
velocity ___________
in this region.
What happens to the P and S waves as they
travel through the layers of earth?
Composition of outer and inner
cores
composed or made up of mostly
nickel and iron because when the
Earth was forming the denser
materials (like iron and nickel)
sank down to the middle.
EARTHS CRUST
Continental Crust
Continental Crust-composed of
granitic rocks with an average
2.7
density of _____
g/cm3 and makes
up the continents. Thicker than
oceanic crust. Thickest under
MOUNTAINS
___________________
while
thinnest under coastal regions.
Oceanic Crust
Oceanic Crust: composed of basaltic
3.0
rocks with and average density of ____
g/cm3. Sometimes as thin as 4 miles
(about 20,000 ft) in places like midRIDGES
ocean ______.
*** Remember oceanic crust is more
dense than continental crust! You will
need to know this for our next topic that
we will be learning about!!