FAULTS

FAULT

• In geology, a fracture in the rocks of the Earth's crust,
• where compressional or tensional forces cause the rocks on the opposite sides
• of the fracture to be displaced relative to each other.
• Most, if not all, earthquakes are caused by rapid movement along faults.
• Faults are common throughout the world.

THERE ARE MANY DIFFERENT KINDS OF FAULTS

• There are:
• DIP-SLIP FAULTS (Reverse Fault or Normal Fault)
• STRIKE-SLIP FAULT. (transcurrent fault, lateral fault, tear fault or wrench fault)
• OBLIQUE-SLIP FAULT

1.DIP-SLIP FAULTS

• a) Normal Fault
• In a normal fault, the block above the fault moves down
• relative to the block below the fault.
• This fault motion is caused by tensional forces and results in extension.
• [Other names: normal-slip fault, tensional fault or gravity fault]

THE NORMAL FAULT

• The normal fault is not necessarily normal in the sense that it is common because it is not the most common
• Of faults. However what is normal about them is that their movement tends to follow the gravitational pull on
• the fault blocks involved. The fault plane on the normal fault is generally very steep. In a normal fault the two
• involved blocks are (by gravity) pulling away from one another causing one of the fault blocks to slip upward
• and the other downward with respect to the fault plane (it is hard to determine whether both or just one.....

THE NORMAL FAULT CONTINUED

• block has moved.).The exposed upward block forms a cliff-like feature known as a fault scarp. A scarp
• may range from a few to hundreds of meters in height and their length may continue for 300 or more kilometers
• (around 200 miles).

1. DIP-SLIP FAULTS CONT'D

• b) Reverse Fault
• In a reverse fault, the block above the fault moves up relative to the block below the fault
• This fault motion is caused by compressional forces and results in shortening.
• A reverse fault is called a thrust fault if the dip of the fault plane is small.
• [Other names: thrust fault, reverse-slip fault or compressional fault]

THE REVERSE FAULT

• The reverse fault is a normal fault except the general movement of the fault blocks is toward each other, not
• away from each other as in the normal fault. This forms a thrust fault type expression on the surface with
• material overlaying other material.

2.STRIKE-SLIP FAULT

• In a strike-slip fault, the movement of blocks along a fault is horizontal. If the block on the far
• side of the fault moves to the left, as shown in this animation, the fault is called left-lateral.
• If the block on the far side moves to the right, the fault is called right-lateral. The fault motion of
• a strike-slip fault is caused by shearing forces.
• [Other names: transcurrent fault, lateral fault, tear fault or wrench fault]

Transcurrent Fault (Strike-Slip Fault)

• Probably the most well known and well studied fault is the transcurrent (strike-slip) fault known
• as the San Andreas fault of California. This fault marks the margin line between the Pacific and North
• American Plates. Movement on a strike strip fault is generally horizontal. On the surface, scarps form as hills
• crossing the fault zone are torn apart by movement over time. Actually anything crossing this fault zone is either
• slowly torn apart, or offset.

3. OBLIQUE-SLIP FAULT

• Oblique-slip faulting suggests both dip-slip faulting and strike-slip faulting. It is caused by a
• combination of shearing and tension of compressional forces.
• Animation Time!
• http://www.iris.edu/gifs/animations/faults.htm

(SORT OF) FUN FAULT FACTS

• Faults range in length from a few centimetres to many hundreds of kilometers
• and displacement likewise may range from less than a centimeter to several hundred
• kilometres along the fracture surface (the fault plane).

THE END!!!!