# Folds and Faults

##### Study Tip
A syncline sinks, so the arch is downwards. An anticline is just the opposite, so the arch is upwards.

## Folds

• Rocks crumple into folds when experiencing a significant amount of stress.
• A monocline is when the rock bends so that the layers are no longer horizontal.
• An anticline is when the rock bends up so there is an upward arch. The oldest layer is at the center, and younger layers are outside. When it arches into a circular structure, it is called a dome.
• A syncline is when the rock bends down so there is a downward arch. The youngest layer is at the center, and the older layers are outside. When it arches into circular structure, it is called a basin.
##### Study Tip
A syncline sinks, so the arch is downwards. An anticline is just the opposite, so the arch is upwards.
##### Study Tip
The same way a person may cast a shadow over another person when they stand under the sun, planets or celestial bodies that have aligned themselves cast shadows over one another as well.
Syncline
Anticline
Monocline

## Faults

• Rocks will break into fractures when experiencing too much stress.
• When there is no movement on either side of the break, the fracture is called a joint.
• When there is movement on one or both sides of the break, the fracture is called a fault.
• The distance one side moves relative to the other is called the slip.
• The angle the fault lies relative to the horizontal surface of the Earth is called the dip.
• If the fault involves vertical movement into the Earth, the fault is a dip-slip fault.
• In a normal fault, the hanging wall drops down relative to the footwall.
• In a reverse fault, the footwall drops down relative to the hanging wall. A thrust fault is a type of reverse fault in where the dip is nearly horizontal, and rocks can slip many miles.
• If the fault involves horizontal movement across the surface of the Earth, the fault is a strike-slip fault, which results from shear stresses. By placing two feet on separate sides of the strike-slip fault,
• If your left foot slips toward you, it is a left-lateral fault.
• If your right foot slips toward you, it is a right-lateral fault.
• California’s San Andreas Fault is a famous right-lateral strike-slip fault.

## Earth Science

Strike-slip faults
Dip-slip faults
##### Concept Check
• Describe the characteristics of a monocline, anticline, and syncline.
• How is a basin formed?
• What is the difference between a joint and a fault?
• What is a thrust fault?
• What kind of fault movement is present in a strike-slip fault? Dip-slip fault?