Transcript Earthquakes - MabryOnline.org

Earthquakes
Chapter 5
Objectives
 Describe how stress forces affect
rock.
 Describe the types of faults, why
faults form and where they occur.
 Describe how movement along
faults changes Earth’s surface.
Have you experienced
an earthquake?
 Describe the event
 Where were you at the time?
 How did you know that it was an
earthquake?
 What happens to the building and
objects around you?
 How did you feel during and after?
Discover Activity
 How Does Stress Affect Earth’s Crust?
 Materials: popsicle stick, goggles
 Page 144
 1. Put on goggles
 2. Holding a popsicle stick at both ends,
slowly bend it into an arch.
 3. Release the pressure on the popsicle
stick and observe what happens.
Discover Activity
 4. Repeat Steps 1 and 2. This
time, however, keep bending the
ends of the popsicle stick toward
each other. What happens to the
wood?
 What do you think might
eventually happen as the forces of
plate movement bend the crust?
Discover Activity
Questions
 When you bent the popsicle stick the
first time and held it in an arch shape,
what was happening?
 Answer: Energy - the “push” applied by
the hands - was being transferred to
the stick and stored in it.
 What would have happened if you had
suddenly let go of one end of the bent
stick, and why?
Discover Activity
Questions
 Answer: the stick would have
sprung back to its original shape
because the stored energy was
quickly released.
 Where did this stored energy go?
 Answer: It was released as energy
in the form of heat.
Introduction
 5.1 video “Why Worry”
 P. 144 in text
Earth’s Crust in Motion
 Stress in the crust
Earthquake - the shaking and
trembling that results from the
movement of rock beneath Earth’s
surface.
Stress - the movement of Earth’s plates
creates powerful forces that squeeze or
pull the rock in the crust.
Stress in the Crust
Volume is the amount of space an
object takes up. (volume cubes)
Types of Stress
-Shearing
-Tension
-Compression
Types of Stress
These types work over millions of years to
change the shape and volume of rock.
Some rocks can become brittle and
snap, others bend slowly like road tar
softened by the sun.
 Shearing - this stress pushes a mass of
rock in two opposite directions. Causes
rock to break, slip apart, or to change
its shape.
 Tension - pulls on the crust, stretching
rock that that it becomes thinner in the
middle.
Types of Stresses
 Compression - squeezes rock until
it folds or breaks.
 Deformation is any change in the
volume or shape of Earth’s crust.
Try This Activity - It’s a
Stretch (p. 145)
 You can model the stresses that create
faults.
 Materials - playdough
 1. Demonstrate the three types of
stresses by:
 A. pushing the ends toward the middle
 B. pull the ends apart.
 C. push half of the putty one way and
the other half in the opposite direction.
Kinds of Faults
 P. 146 - Read first paragraph.
 Fault - a break in Earth’s crust
where slabs of crust slip past each
other. They usually occur along
plate boundaries where the forces
of plate motion compress, pull, or
shear the crust so much that the
crust breaks.
Three main types of
faults
 Strike-slip fault
 Normal faults
 Reverse faults
Strike-slip fault
 Strike-slip fault shearing causes
these faults. Rocks
on either side of the
fault slip past each
other sideways with
little up-or-down
motion. They also
form transform
boundaries.
 Example - San
Andreas fault
Strike-Slip Fault
 P. 146 - Irregular, shadowed line
running up the middle of the
photograph. Look at the road at the
bottom of the photograph.
 If a strong earthquake occurred, what
do you think would happen to the road
where it crosses the fault? Why?
 Answer: The road would be bent out of
alignment or broken because the two
slabs of crust on opposite sides of the
fault are moving in different directions.
Strike-Slip Fault
 What other things might be
deformed or broken at a fault?
 Answer: Fences, rivers and
streams, bridges, driveways,
straight rows of trees or crops, etc.
Normal fault
 The fault is at an
angle, so one
block of rock lies
above the fault
while the other
block lies below
the fault.
Normal Fault
 The half of the
fault that lies
above is called
the hanging wall.
 The half of the
fault that lies
below is called
the footwall.
 Facts & Figures p. 146 TE
Normal Fault
 P. p. 146 - Figure 4 Sandia
Mountains in New Mexico.
 Tension forces create normal
faults where plates diverge, or pull
apart.
Normal Fault - Rio
Grande Valley
Reverse Faults
 Compression
produce reverse
faults.
 It is like a normal
fault but the
blocks move in
the opposite
direction.
 P. 147- Figure 5
Reverse Fault
 Mt. Gould in Glacier
National Park,
beginning 60 million
years ago. Which
half of the reverse
fault slid up and
across to form this
mountain, the
hanging wall or the
footwall?
Reverse Fault Appalachian Mountains
Building Inquiry Skills:
Application Concepts
 How could you use your hands to
demonstrate a:
 Strike-slip fault
 Normal fault
 Reverse fault
Exit Slip
 Make a simple sketch of each type
of fault without referring to the
diagrams on the pages, add
arrows to schow the bock
movements, and label each sketch
thewith name of the type of fault it
shows. Put in journal if you have
one.
Friction Along Faults
 What is friction?
 What are some examples of low friction
that you’ve experienced?
 Low friction - ice or polished floor
 What are some examples of times when
people use high friction to their
advantage?
 High friction - sanding, rubber-soled
sneakers, filing fingernails
Friction Along Faults
 Friction is the force that opposes
the motion of one surface as it
moves across another surface.
 Read p. 148
 San Andreas Fault - Friction is
high.
Mountain Building
 Over millions of years, fault movement
can change a flat plain into a towering
mountain range.
 Mountains Formed by Faulting When
normal faults uplift a block of rock, a
fault-block mountain forms.
 Teton Range near Wyoming and Idaho
was formed this way. (Slide Show)
Mountains Formed by
Folding
 Have you ever skidded on a rug
that wrinkled up as your feet
pushed it across the floor?
 Folds - bends in rock that form
when compression shortens and
thickens part of Earth’s crust.
Himalayas in Asia caused by folds
Alps in Europe - caused
by folds
Anticlines and
Synclines
 Anticline - A fold
in rock that bends
upward into an
arch.
 Syncline -A fold in
rock that bends
downward in the
middle to form a
bowl.
Anticline
Syncline
Plateaus
 Large area of flat
land elevated
high above sea
level.
 500 km across
and 1500 meters
above sea level.
 Grand Canyon
pictures.
Modeling Movementa
Along Faults Lab
 Problem - How does