Geological Faults

Geological faults are breaks in the Earth’s crust. They can be caused by tension, compression or shearing forces, which the outermost layer of the planet constantly undergoes. Thus, there are three types of faults: normal fault, thrust fault, and strike/slip fault. Earthquake is associated by these geological features.

Normal fault

It is created when tension forces stretch the crust, which is constituted by either basalt or granite rocks. When the fault stretches to its breaking point, the rocks are moved along the direction of this force, causing an earthquake. A normal fault rips the crust at an angle; thus, a large piece of rock slides up as the other piece of geological material slides down, with the rocks that slides up becoming either mountains or plateau, while the rocks that slides down turning into rifts or river valleys. The Franklin Mountains of Texas, and Rio Grande rift is examples of this, respectively.

Thrust fault

Also called reverse fault, it is formed when compression forces smash the crust together. When the rock layer get ripped, it breaks at angle similar to a normal fault. This type of fault also creates mountains and rifts. Most mountains in Southern California are the consequences of thrust fault movements. The San Gabriel mountains, for example, are constantly being pushed up and over the rocks of the San Fernando and San Gabriel Valley by a thrust fault.

Strike/slip fault

It arises when shearing forces push two blocks of rocks sideways (horizontally) in opposite directions. Contrary to the above-mentioned faults, in this case there is very little up and down motion. Instead, when the layer of rock breaks, the two pieces of broken land slide past each other in a side by side motion. Although it does not form mountains and valleys, this type of fault causes very strong earthquake. The San Andreas fault is an example of strike/slip one.