Earth Science

Geological Activity from Plate Tectonics Processes

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.
Folds
Syncline
Syncline
Anticline
Anticline
Monocline
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.
Faults
  • 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‚Äôs San Andreas Fault is a famous right-lateral strike-slip fault.

Earth Science

Strike-slip faults
Strike-slip faults
Dip-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?