The Earth’s Internal Properties
I. Seismic Waves
A. = Earthquake-generated waves
traveling through the
Earth’s interior
B. Give us clues to the composition of the
Earth
C. Types of Seismic Waves
1. Surface waves –
travel on the Earth’s surface
2. Body waves –
travel through the Earth’s
interior
Body waves
a.



P-waves (primary waves)
Compress and expand rock
Are the fastest of all seismic waves
First waves to register on
seismograph
Body waves
b. S-waves (secondary waves)
 Vibrate up and down
 Second waves to register on a
seismograph
Seismograph
= Device which measures seismic
waves
II. Earth’s internal layers


Geologists did research with seismic
waves
Concluded that the Earth’s
interior is layered.
Earth’s internal layers
Earth’s internal layers
A. The Core1. Composed
mostly of iron
and nickel
2. Inner Core
 very hot

solid Fe & Ni
due to high
pressure of the
Earth
The Core (continued)

3.Outer Core
 less pressure
from the earth
 liquid Fe & Ni
 Flow in the outer
core generates
an electric
current that
powers the
Earth’s magnetic
field.
B. The Mantle


Rocky layer
About 3000km thick
1. Two parts of mantle
a. Lower mantle
b. Upper mantle –
two sections
b. Upper mantle
i.
Asthenosphere - behaves in a semi-fluid
manner
b. Upper mantle
ii. Lithosphere- rigid and brittle
C. The Crust
1.
2.
Uppermost portion of the lithosphere
Two types of crust
a. Oceanic crust - about 10 km thick
C. The Crust
b. Continental crust –
about 20-60 km thick
III. Theory of Continental Drift
A. Belief that the earth is a dynamic
planet with the continents in constant
motion (i.e. continents are moving)
III. Theory of Continental
Drift
B. All continents once
joined together
into supercontinent
called Pangea
(meaning = all land)
C. Theory formulated
by Alfred Wegener
III. Theory of Continental
Drift
D. Evidence that supports theory =
1. Geologic (rock)
2. Biologic (life)
3. Climatological
(past weather)
4. Continental Shelves fit together very
well
Tectonic Plates
= moving sections of the lithosphere
on which continents lie
IV. Faults
fault = a fracture along which visible
displacement can be detected on one
side relative to the other.
B.
Types of faults
1.
Footwall-Fig 23.17
(“one on bottom”)
A.
Footwall
B. Types of faults
2. Hanging wall- Fig 23.17 (“one on
top”)
V. Vertical movement along a
fault
1. Reverse Fault- Fig 23.18- Footwall
down
Examples:

Rocky Mountains

Canadian Rockies

Appalachian Mts.
V. Vertical movement along a
fault
2. Normal Fault- Fig 23.19- Footwall up
VI. Horizontal movement along a
fault boundary (Fig. 23.22)
A.
Transform-fault boundary –
plates are sliding past one another
(Figs. 23.27 & 28)
E.g. San Andreas fault in
California
★ Earthquakes caused by sheering forces
B. Divergent Boundaries
1. two plates are moving apart
(Fig. 23.23)
 Plate A Plate B 
2. Creates rift valleys –
large spreading valleys
at fault line
3. Creates sea floor spreadinga rift valley on sea floor
4. Caused by tensional forces
B. Divergent Boundaries
C. Convergent Boundaries
1. Two plates move towards each other
(Fig 23.24)
Plate A 
 Plate B
2. Leads to subduction- one plate
(usually oceanic crust)
goes beneath the other
(continental crust).
 Caused by compressional forces
C. Convergent Boundaries
C. Convergent Boundaries
E. g. Andes Mountains in S. America
(Still growing because of subduction)
3. ★Common place to find volcanoes
E.g. Cascade Range
(Mt. St. Helens,
Mt. Rainier…)
Tectonic Plate Movement
Major Tectonic Plates