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Earthquakes
Chapter 19
Crustal Movement:
Stress – The total force acting on crustal rocks per
unit of area.
3 TYPES OF STRESS:
Strain – The deformation of
materials in response to stress.
Strain (deformation)
Elastic vs. Plastic
Caused when a material is
compressed, bent or stretched.
Caused when a material is
permanently deformed.
Similar to stretching a rubber
band by pulling on the ends.
Similar to pulling a rubber
band until it actually breaks.
• The
point at which Earth’s crust has reached its elastic
limit is when permanent deformation occurs.
Folds (elastic deformation) – There
are 2 types of bends that can occurs in
Earth’s crust.
Syncline “sinks”
Anticline folds up
like a capital “A”
Faults (plastic deformation) – breaks
in the Earth’s crust along which
Earth’s crust moves.
Faults produce 2 sides (walls):
Foot wall –
The side of the
fault which is
thicker at the
bottom (you can
“walk” up it)
Hanging wall –
The side of the
fault which is
thicker at the
top (you can
“hang” from it)
TYPES OF FAULTS
Normal Fault – Tension pulls rock apart, forcing the
footwall up and the hanging wall down.
Normal Fault
Animation
Normal Fault
Stress =
Tension
TYPES OF FAULTS
Reverse Fault – Compression causes the hanging wall
to move up and the footwall to move down.
Reverse Fault
Animation
Reverse Fault
Stress =
Compression
TYPES OF FAULTS
Strike-Slip Fault – Shearing forces two parts of
Earth’s crust past each other with NO vertical
movement.
Strike-Slip
Animation
Strike-Slip
Fault
Stress =
Shearing
Reverse, Normal, or Strike-Slip Fault?
Normal Fault
Tension
Hanging Wall Sinks Down
Reverse, Normal, or Strike-Slip Fault?
Reverse
Compression
Hanging wall is pushed up
Reverse, Normal, or Strike-Slip Fault?
Strike-Slip
Shearing
No Vertical Movement
Earthquakes – The vibration of Earth’s
surface following a release of energy from Earth’s crust.
Focus – The point
Underground where an
earthquake originates.
Epicenter – The point on
Earth’s surface directly above
the focus. This is typically the
location we about on the
news.
Inside Earthquakes Video
Interior seismic waves – These waves
travel through the inner layers of Earth.
Primary Waves
Secondary Waves
-Travel twice as fast
as S-Waves.
-Travel half as fast as
P-Waves.
-Compressional
Movement: rocks are
squeezed and pushed
in the same direction
as the wave moves.
-Rolling Movement:
rocks shifted up and
down perpendicular to
the direction of the
wave.
-Move similar to a
slinky that is
stretched and then
released.
-Move similar to a
rope that is being
shaken up and down.
COMPARE P WAVES AND S WAVES
Shadow Zones – Areas on Earth where no seismic waves are recorded.
-P waves can travel
through all of the
layers (solid, liquid
and plastic), but they
are deflected in
different directions as
they move from one
layer to another.
-S waves can travel
through solid and
plastic layers, but not
liquid layers (the outer
core).
Shadow Zones
Surface seismic waves – These are the slowest of
the seismic waves and they only travel on Earth’s surface.
Love waves cause a side to
side movement of the
surface.
Raleigh waves cause an
up and down movement of
the surface.
-When combined, these waves move the ground up and down and side to side
simultaneously.
-They cause the most damage because the create the most ground movement and
take the longest time to pass an area.
Locating the epicenter of an Earthquake: Triangulation
Scientists use seismic
data received from at
least 3 stations to
triangulate (the same
process GPS uses) the
epicenter of an
earthquake.
We will explore this
process more in lab.
How do we measure earthquakes?
Richter Scale
Mercalli Scale
-Created by Charles Richter in 1934.
-This scale measures earthquakes
based on the largest seismic wave
recorded during a quake.
-The original scale used to measure
quakes. Created in 1902 by
Giuseppe Mercalli.
-Considered less accurate, because
it uses eyewitness observations of
damage to estimate the intensity of
the quake.
-The scale is from 0-10. Every whole
number up on the scale represents an
increase in energy of ten times more.
MERCALLI SCALE
Moment Magnitude Scale
**This is the most accurate scale used today**
-Introduced in 1979.
-Measures earthquake strength based on the amount of energy released by calculating size of
the fault, amount of movement, and type of rock (stiffness).
-The moment magnitude scale is preferred over the Richter scale by seismologists because it
is more accurate.
-When hearing about an earthquake on the news, this is typically the final, most accurate
magnitude given.
Earthquake
Richter Scale
Moment Magnitude
New Madrid, MO, 1812
8.7
8.1
San Francisco, CA 1906
8.3
7.7
Prince William, AK 1964
8.4
9.2
Northridge, CA,1994
6.4
6.7
Earthquake Depth
Shallow
earthquakes cause
the most damage.
Intermediate
earthquakes cause
moderate damage
Deep earthquakes
cause the least
damage.
Earthquake Hazards: Structural Failure
Earthquake Hazards: Land/Soil Failure
Earthquake Hazards: Tsunamis
A series of waves that occurs when the ocean is
disturbed by earthquakes, underwater explosions or
impacts.
tsunami animation