Lecture #6: Faults and How They Form
(Abbott, pp. 30-32, 79-87)
What are Faults?
Rocks may fracture, especially in and near plate tectonic boundaries.
If rocks on either or
both sides of a fracture move in a direction parallel to the fracture, the fracture is called a
(Figure 4.2, p. 79)
Faults may range in length from a few centimeters to hundreds
Movement along a fault may be gradual and barely noticeable.
On the other hand,
movements may also be sudden, significant and rapid, which generate
such cases, the rocks usually undergo a series of movements that produce multiple
earthquakes of various intensities over hours, days, or even longer (p. 85); that is,
earthquakes may involve foreshocks, the main earthquake, and aftershocks.
faults are the chief causes of earthquakes, earthquakes may also result from landslides,
collapsing cave roofs, underground nuclear explosions, and magmas pushing through
rocks in the subsurface.
Producing Faults through Rock Deformation
refers to forces
affecting a rock (p. 31), which may cause rocks along faults to
move and generate earthquakes (p. 79-80).
If the stresses are intense enough to deform
the size and shape of a rock, the resulting deformation
Stress and Strain (Stress is the force and strain is the result):
Three major types of forces or stresses may deform rocks and possibly produce faults and
earthquakes; namely, tension, compression, and shearing.
squeezes and shortens a rock.
grinding of two rocks by pushing them past each other in opposite directions, such as