Diastrophism refers to the series of processes by which the major features of Earth's crust are formed and changed because of relative changes of positions and deformation of rock, which may be sudden, causing earthquakes, or slow, which have far-reaching effects on Earth. Two major types of slow structural deformations are folding and faulting. Folding occurs when rocks buckle or fold due to horizontal or vertical pressure. They are shaped into an arch (called anticline) or a trough (called syncline), or they may override an adjacent fold.
Click below, and view slides 21 through 27.
Faults are fractures in the Earth's crust caused by forces acting on the crust due to slow rock movement within the asthenosphere. Vertical forces produce uplifts, while horizontal ones produce compression or tension. The fault plane is the actual surface itself. The hanging wall is the rock on the upper side of the inclined fault plane, and the footwall is the underside. Although faults can be vertical or horizontal, most faults are inclined at an angle. The three types of faults are normal, reverse, and strike-slip.
A normal fault occurs when its overlying side (hanging wall) moves downward relative to the footwall. As the stress forces are in opposite directions, the crust is pulled apart. A reverse fault occurs when compressional stress forces cause the hanging wall to move upward relative to the footwall. A special case is thrust faulting when the fault plane is at a small angle to the horizontal. This generally happens along convergent plate boundaries. Strike-slip faulting occurs when stresses are parallel to the fault boundary, and fault slip is horizontal. It commonly occurs along transform faults near plate boundaries that do not directly move toward or away from each other.
Click below and view slides 28 through 32
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