Types of Faults

TYPES OF FAULTS

The crust of the Earth is broken into large sections called plates. These plates float on a partially melted portion of the mantle called the asthenosphere. Due to unequal heating of the asthenosphere, convection currents form causing the asthenosphere to slowly move.

When the asthenosphere moves, the plates that are floating on the asthenosphere also move. As the plates move, great stress or force is being applied to the rock layers that make up the plates. As the plates continue to move, more and more stress is built up within the rock layers until the rocks can no longer withstand the strain and they break. This is very similar to a rubber band which is stretched too far. It will eventually snap. When the rock layers of the Earth break, enormous amounts of energy are release and an earthquake occurs.

Whenever there is an earthquake, chances are that the starting point or the epicenter of the earthquake occurred along a fault. A fault is a crack in the Earth's crust where movement occurs. There are three main types of faults: normal fault, reverse or thrust fault and a strike-slip fault.

Normal Fault

Normal faulting is caused by tension. At a normal fault, the Earth's crust is being pulled apart and a section of the crust drops downward causing a rift to appear. Normal faults are associated with divergent plate boundaries

Normal Fault

Reverse Fault

A reverse fault, also known as a thrust fault, is caused by compression. This type of stress is found at convergent boundaries and it is associated with the formation of mountains on land. When the plates collide, a section of the crust is forced upward. If the plates continues to collide, more and more of the crust will be forced upward forming a mountain.

Thrust Fault

Strike-Slip Fault

A strike slip or transform fault is caused by the lateral movement of two tectonic plates. As the plates slide by each other at a transform plate boundary, lateral displacement occurs. Most of the major faults in the United States are strike-slip faults. The San Andreas Fault in California is largest and most well known example of a strike-slip fault.

Left Lateral Fault

Lateral Displacement

As the plates move, the fence and the

river are no longer in a straight line.

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