What Are the Three Types of Earthquakes Faults?

When an earthquake is occurring most people effected do not care what type of fault created the earthquake. However there are three different types of faults and the exact type can effect the amount of damage from the earthquake. Earthquakes that cause the most damage come from plate movement that is prevented when the plates lock due to friction. There are also four different parts to a fault itself.

Parts of a fault:

The fault itself consists of four parts. The first part is the fault plane or area where the fault occurs. This surface area may be sloping or vertical. The second part is the fault trace. The trace is the line, visible or not, that occurs on the Earth's surface. The third part of a fault is the hanging wall and the fourth part is the footwall. In a sloping fault plane, the upper side of the plane area is referred to as the hanging wall and the lower side of the plane is the foot wall.

Strike-slip faults:

The walls in a strike-slip fault move sideways. The force that creates the movement is horizontal or lateral and moves the sides past each other. These types of faults usually occur on a vertical plane with no footwall or hanging wall. The motion experienced is not up and down as much as it is right or left lateral. The San Andreas fault is a strike-slip fault.

Normal faults:

In a normal fault the hanging wall drops downward. The force that creates this type of fault is trying to pull the sides apart. While called a normal fault, a normal fault is not the most common of all faults. The term normal refers to the tendency for the movement of this type of fault to follow gravitational pull. The Cabrillo fault is an example of a normal fault.

Reverse faults:

In a reverse fault the hanging wall moves in an upward direction. The force behind this is causing compression and trying to push the walls together. Reverse faults are also sometimes referred to as thrust faults. The term thrust fault is used to identify a fault with one or more plates under the ocean. Thrust faults can produce more damage than strike-slips faults. The Sumatra earthquake in December of 2004 is an example of a reverse fault quake.

Both normal and reverse faults are also referred to as dip-slip faults. The movement on normal or reverse faults will cause an up or down motion. In most faults a combination of both dip-slip and strike-slip motion occurs. It is the shaking of an earthquake that damages buildings the most. At the same time a large strike-slip can cut or tear buildings or roadways in half.

References:

http://www.exploratorium.edu/faultline/basics/faults.html

http://geology.about.com/library/bl/blbeachball.htm

http://geology.about.com/gi/dynamic/offsite.htm?site=

http://www.naturalfractures.com/1.1.4.htm