Earth Science
Chapter 5
Section 1
A. Stress in the Crust:
-An earthquake is the shaking and trembling that results from
the movement of rock beneath Earth’s surface.
The movement of Earth’s plates create powerful forces that
squeeze or pull the rock in the crust.
B. Types of Stress:
-Three types of stress occur in the crust.
- Shearing – stress that pushes a mass of rock in two
opposite directions .
- Tension – pulls on the crust, stretching rock so that it
becomes thinner in the middle. Tension occurs where two
plates are moving apart.
- Compression – squeezes rock until it folds or breaks.
Occurs when two plates move toward each other.
-A change in the crust is known as deformation.
Examples: Bend, stretch, tilt, fold, and slide.
C. Kinds of Faults:
-A fault is a break in the crust where slabs of crust slip past
each other. The rocks on both sides of a fault can move up or
down or sideways.
-Faults usually occur along plate boundaries, where the forces
of plate motion compress, pull or shear the crust.
-Three Types of Faults:
1. Strike-slip faults – A fault that occurs as two plates slip
past one another in a side to side motion. This fault occurs
at a Transform plate boundary.
2. Normal faults – The fault is at an angle, one block of rock
is above the fault and the other is below the fault. Form
due to tension.
Hanging Wall – The half of the fault that lies above the
fault.
Footwall – The half of the fault that lies below the
fault.
3. Reverse fault – This fault has the same structure as the
Normal Fault. During compression the hanging wall is
forced upward over the footwall.
D. Friction Along Faults:
Low friction- The rocks on both sides of the fault slide by each
other without much sticking.
Moderate friction- The sides of the fault jam together, Then
jerk free, producing small earthquakes.
High friction- The rocks lock together and do not move. Here
stress builds up until it overcomes the friction and produces a
powerful earthquake.
E. Mountain Building:
Mountains formed by Faulting:
- When normal faults uplift a block of rock, A Fault-block
Mountain forms.
Mountains formed by Folding:
- Folds are bends in rock that form when compression
shortens and thickens part of the Earth’s crust.
- Plate collisions cause the crust to bend and fold.
- Some of the largest mountains in the world are folded
mountain ranges. The Himalayas in Asia and the Alps in
Europe are examples.
F. Anticlines and Synclines:
- The upward and downward folds created by compression
have been given names by geologists.
- Anticlines – An upward fold of rock.
- Synclines – A downward fold of rock.
G. Plateaus:
The forces that raise mountains can raise plateaus. A Plateau is
a large area of flat land elevated high above sea level.
Some plateaus form when vertical faults push up large flat
blocks of rock, such as the Colorado Plateau.