Earthquakes
 An earthquake is shaking or movement of the Earth.
 They are caused by plate tectonics.
Faults
 Earthquakes occur on
faults. Faults are
fractures along blocks
of rock
 Faults allow the blocks
to move relative to one
another
Types of Faults
 The direction and angle of the slip determines the type of
fault.
 The type of fault determines the type of earthquake.
 During an earthquake, the rock on one side of a fault moves
in relation to the other side. This is called slip.
 Most faults produce repeated displacement of blocks over
geologic time
Strike-Slip Faults
 Strike-slip faults are
nearly vertical
fractures where the
blocks have moved
mostly horizontally.
 strike slip animation
Strike-Slip Fault Example
 Strike-slip faults occur in
regions with transform
boundaries, such as , the San
Andreas Fault.
Bigger Faults=Bigger Earthquakes
Kilometers
1000
100
10
1
5.5
6
6.5
7
Magnitude
7.5
8
More time=Bigger Earthquake
Seconds
100
10
1
5.5
6
6.5
7
Magnitude
7.5
8
Normal Faults
 Normal faults are faults
where one block has
moved downward.
 These faults are seen in
areas where there are
divergent boundaries
 Normal Fault Animation
Normal Fault Examples
Valley-Fairview Peaks, Nevada
earthquake
December 16, 1954
Reverse Fault
 Reverse faults are
faults where one block
moves upwards
 Thrust faults are
reverse faults
movement of 45
degrees or less
 Reverse Fault
Animation
Reverse Fault Example
 Reverse faults can
be found in areas
with convergent
boundaries. There
needs to be
subduction zones
for reverse faults to
occur.
Magnitude
 The magnitude of an earthquake is a measure of the
amount of energy released by the earthquake.
Amount of Shaking
 The amount of shaking is controlled by:
 Magnitude
 More
energy released
 Distance
 Shaking
decays with distance
 Local soils
 amplify
the shaking
Seismic Waves
 When an earthquake occurs, it releases energy in the
form of seismic waves.
 The different types of energy waves shake the ground
in different ways and also travel through the earth at
different velocities.
Types of Waves
 There are two categories of
waves:

Body waves travel through the
Earth’s interior

Surface waves travel along or near
the earth’s surface.
Body Waves
 A P wave, or
compressional wave, is
a seismic body wave that
shakes the ground back
and forth in the same
direction and the opposite
direction as the direction
the wave is moving.
P Waves
 The fastest wave, and therefore the first to arrive at a
given location, is called the P wave. The P wave, or
compressional wave, alternately compresses and
expands material in the same direction it is traveling
Body Waves
 An S wave, or shear
wave, is a seismic
body wave that shakes
the ground back and
forth perpendicular to
the direction the wave
is moving.
S Waves
 The S wave is slower than the P wave and arrives
next, shaking the ground up and down and back and
forth perpendicular to the direction it is traveling.
Types of Waves
 There are two categories of
waves:

Body waves travel through the
Earth’s interior

Surface waves travel along or near
the earth’s surface.
Surface Waves:
Surface waves follow the P and S waves.
 A Rayleigh wave is a
seismic surface wave
causing the ground to
shake in an elliptical
motion, with no
transverse, or
perpendicular,
motion.
Surface Waves
 A Love wave is a
surface wave having a
horizontal motion that
is transverse (or
perpendicular) to the
direction the wave is
traveling.
Magnitude
An estimate of the energy of an earthquake is called the
Seismic Moment (Mo). Typically given in units of
Newton-meters (Nm)
What factors contribute to the amount of energy released by an
earthquake?
 S = Surface Area of Fault (m2) (Fault length x Fault width)
 D = Displacement or slip (m)
 µ = Rigidity of rock along the fault (N/m2)
 Mo = S*D* µ