The San Andreas Fault in California is an example of a strike-slip fault.
Earth's surface isn't a rigid mass, rather the crust is composed of plate tectonics that can shift. A fault is a crack in Earth's crust that usually occurs around the boundaries of these plates. Faults form when the stresses acting on the rock overcome the rock's internal strength, and it fractures. When the plate tectonics shift roughly at the faults, earthquakes, like the 2011 magnitude 9.0 Tohoku-Oki earthquake in Japan, can result.
Normal Dip-Slip Fault
In a normal dip-slip fault, tension pulls the rock on either side apart. The rock on one side of the fault moves down relative to the other rock slab.
Reverse Dip-Slip Fault
In a reverse dip-slip fault, the forces acting on the rock slabs are compressing them so that the rock slab on one side is pressed up and over the slab on the other side of the fault. A reverse fault often results in an overhang or cliff.
Strike-Slip Fault
A strike-slip fault does not involve a rock slab moving up or down relative to each other. Instead, the rock slabs move horizontally against each other, forward or backward. The San Andreas Fault in California is a famous example of the strike-slip fault, also called a transform fault. It is one of the few examples of a strike-slip fault occurring on land; the majority of strike-slip faults are found on the ocean floor and contribute to shallow earthquakes.
Graben Fault
Graben faults, known as rift valleys when they occur on a large scale, result when the pulling apart of rock slabs results in a block of rock falling from the center. Grabens are common sites for aquifers and groundwater basins. Grabens are also seen in the East African Rift System, which is a geologic wonder of the world because Earth's forces are currently splitting apart existing plate tectonics to create new ones.
Horst Fault
A horst fault is a graben fault in reverse; compressional forces cause a block of rock to be pushed up. Horsts are likely sites of oil reservoirs.
Earthquakes
Earthquakes often occur along faults.
Faults are considered geologic "weak zones," so construction projects around them must be limited. When the movement of the rock slabs along a fault is hindered by friction, the slabs can get stuck. Eventually enough force is built up to allow the rock to break free and overcome the friction, but the result is an earthquake. Earthquakes can also give rise to tsunamis -- massive ocean waves -- if they occur on the ocean floor.
Tags: rock slabs, plate tectonics, rock slab, strike-slip fault, acting rock, Andreas Fault
