Download AICE Env Day 1 Types of Faults Foldable Booklet

AICE Environmental Management
Unit 2: Lithosphere – Earthquakes & Volcanoes
Foldable: Types of Faults
Background Information:
Earthquakes occur when there is a sudden movement on the Earth’s crust. Most movement on the
Earth’s crust takes place along plate boundaries. There are three main types of plate boundaries; they
include converging (moving together), diverging (moving apart), and sliding or transform plate
boundaries. There is a direct correlation between the plate boundary and the type of fault associated
with an earthquake.
A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move
relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur
slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of
kilometers. Most faults produce repeated displacements over geologic time. During an earthquake, the
rock on one side of the fault suddenly slips with respect to the other. The fault surface can be
horizontal or vertical or some arbitrary angle in between.
Figure 1: Types of Faults
Normal Fault
In a normal fault, the fault plane is nearly vertical. The hanging wall, the block of rock positioned above
the plane, pushes down across the footwall, which is the block of rock below the plane. The footwall, in
turn, pushes up against the hanging wall. These faults occur where the crust is being pulled apart, at a
divergent plate boundary.
Reverse Fault
The fault plane in a reverse fault is also nearly vertical, but the hanging wall pushes up, and the footwall
pushes down. This sort of fault forms where a plate is being compressed. A thrust fault moves the
same way as a reverse fault, but at an angle of 45 degrees or less. In these faults, which are also
caused by compression, the rock of the hanging wall is actually pushed up on top of the footwall at a
convergent plate boundary.
Strike-slip Fault
In a strike-slip fault, the blocks of rock move in opposite horizontal directions. These faults form when
crust pieces slide along each other at a transform plate boundary. The San Andreas Fault in California
is one example of a transform plate boundary.
Front Cover:
NORMAL
FAULT
REVERSE
FAULT
STRIKE-SLIP
FAULT
Inside:
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Sketch of the fault.
Type of Boundary:
Description of what is happening.
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