Download Table of Contents - Mr. Tobin`s Earth Science Class

Title: 19.1 Forces Within Earth
Page #:
Date: 6/6/2013
 Students
will be able to define stress and
strain as the apply to rocks.
 Students will be able to distinguish
among the three types of movement of
faults.
 Students will be able to contrast three
types of seismic waves.
 Fracture: The
texture or general
appearance of the freshly broken surface
of a mineral.
 Main
Idea
 Pg. 528
 Faults: Form
when forces acting on
a rock exceed the rock’s strength.
 Stress
&
Strain
 Pg. 528
 Stress
and Strain:
• Earthquakes are the result of
movement of Earth’s crust, produced
by plate tectonics.
• Stress: Total force acting on crustal
rocks pre unit of area.
 Plates move gradually.
 Stress builds up over time.
Stress builds up over time and eventually rocks will break.
 Stress
 Pg. 528
3
Kinds of Stress:
1. Compression: Stress that decreases
the volume of a material.
2. Tension: Stress that pulls material
apart.
3. Shear: Stress that causes material to
twist.
 Strain
 Pg. 528
 Strain: The
deformation of
materials in response to stress.
 Earthquakes: Result
when Stress
and Strain reach a critical point.
 Pg. 529
Types of
Strain
 Elastic
Deformation: When
material is compressed, bent, or
stretched.
• Occurs from low stress.
• Material returns to normal when
stress is removed.
 Plastic
Deformation: Permanent
deformation.
• Occurs at high stress (passed elastic
limit.
• Deformation stays when stress is
removed.
Deformation of Rocks.
When rocks bounce
back the deformation
is elastic. When rocks
are deformed
permanently the
deformation is plastic.
 Pg. 529
Types of
Strain
 Most
materials show both elastic
and plastic deformation.
 As pressure builds up, elastic limit
increases.
 As temperature increases, stress is
reduced.
 Pg. 529
Faults
 Faults: Any
fracture or system of
fractures along which Earth
moves.
• A weak spot in the crust.
 Fault
Plane: Surface along which
Earth moves.
• Can be horizontal to vertical.
 Pg. 530
Faults
 Reverse
and Normal Faults:
 Reverse Fault: Forms from
compression, one piece of crust
gets pushed up.
• Convergent plate boundaries.
 Normal
Fault: Form from tension
pulling two pieces of crust apart
and one piece of crust slips down.
Reverse Fault
 Pg. 531
Faults
 Strike-Slip
Fault: Caused by
horizontal shear.
• Two pieces of crust move in opposite
directions and rub past each other.
• Example: San Andreas fault.
Normal Fault
Reverse Fault
Strike-Slip Fault
 Pg. 532
Waves


1.
2.

Earthquake Waves:
3 Types of Seismic Waves:
Primary Wave: P-Waves. Squeeze and
push rocks in direction in which wave
is traveling.
Secondary Wave: S-Waves. Slower than
p-waves. Rocks move at right angles
in relation to direction of waves.
Both P and S waves pass through
Earth’s interior.
 Pg. 532
Waves

Earthquake Waves:
Surface Wave: Slowest type of
wave. Travel only along Earth’s
surface.
3.
•
•
Move up and down and side to side.
Cause the most destruction
because the are the shortest to pass
an area.
Surface Wave.
 Pg. 533


Waves

Generation of Seismic Waves:
Focus: Point where waves originate,
result of failure of crustal rocks.
Epicenter: Point on Earth’s surface
directly above the focus.
• Surface waves originate and spread
out from epicenter.