Transcript Guided Notes for Forces Within Earth

Guided Notes for
Forces Within Earth
Section 19.1
1) Earthquakes are natural vibrations
of the ground caused by movement
along gigantic fractures in the
Earth’s crust.
2) Most earthquakes occur when
rocks fracture deep within Earth’s
crust. Fractures form when stress
exceeds the strength of the rocks
involved.
3 Kinds of Stress That Act
on Rocks
 Compression: stress that decreases
the volume of a material  pushing
together
 Tension: stress that pulls a material
apart
 Shear: stress that causes a material
to twist
4) The deformation of materials in
response to stress is called
strain.
5) Elastic strain causes a material to
bend and stretch, and can be
demonstrated by applying tension to
a rubber band. Elastic strain is
proportional to stress, and thus, if
the stress is reduced to zero, the
strain disappears.
6) When stress exceeds a certain
value, a material undergoes ductile
deformation. This type of strain
produces permanent deformation,
which means that the material is
deformed even if the stress is
reduced to zero.
7) Most rocks are brittle under the
relatively low temperatures that exist
in the crust, but become ductile at
the higher temperatures at greater
depths.
8) Rocks that make up Earth’s crust
fail when stress is applied too
quickly, or when stress is too great.
9) Define Fault and Fault
Plane
 Fault: the fracture or system of fractures
that occur as a result of stress and along
which movement occurs
 Fault Plane: the surface along which
movement takes place
The 3 Types of Faults
Reverse Faults
 Form because of horizontal compression
 Result in a horizontal shortening of the
crust
The 3 Types of Faults
Normal Faults
 Caused by tension
 Movement is both vertical and horizontal
The 3 Types of Faults
Strike-Slip Faults
 Caused by horizontal shear
 Movement is horizontal
11) Most earthquakes are caused by
movements along faults. Irregular
surfaces in rocks can snag and lock.
As stress continues to build in these
rocks, they reach their elastic limit,
break, and produce an earthquake.
12) The vibrations of the ground
during an earthquake are called
seismic waves. Every earthquake
generates 3 types of seismic waves.
3 Types of Seismic Waves
Primary Waves
 These waves squeeze and pull rocks in
the same direction that the wave travels.
3 Types of Seismic Waves
Secondary Waves
 Can cause rocks to move at right angles
to the direction of travel of the wave
3 Types of Seismic Waves
Surface Waves
 Cause rocks to move both up-and-down
and side-to-side as the wave passes
through
Define Focus and
Epicenter
 Focus: the point within the earth’s crust
where an earthquake originates
 Epicenter: the point on the earth’s
surface directly above the focus