150Lec6-1 - Lecture #6: Faults and How They Form (Abbott,...

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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 fault (Figure 4.2, p. 79) . Faults may range in length from a few centimeters to hundreds of kilometers. Movement along a fault may be gradual and barely noticeable. On the other hand, movements may also be sudden, significant and rapid, which generate earthquakes . In 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. Although 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 Stress 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 is called strain (p. 31). 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. Tensional stress pulls rocks apart. Compressional stress squeezes and shortens a rock. Shearing stress involves the grinding of two rocks by pushing them past each other in opposite directions, such as
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This note was uploaded on 07/14/2011 for the course GLY 150 taught by Professor Henke during the Spring '08 term at Kentucky.

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150Lec6-1 - Lecture #6: Faults and How They Form (Abbott,...

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