NOTES

FAULTS and FOLDS

What is a fault?

A fault is a fracture or series of fractures in Earth’s crust that occurs when stress is applied too quickly or stress is too great.

Many faults occur along plate boundaries.Faults can also occur anywhere in the crust where

rocks are bent (folded) until they break. Faults occur as a result of various types of stress.

Stress is the force that acts on a material.

Strain is the deformation (change of shape) of a material in response to stress.

Stress vs. Strain

Most Faults Have a Hanging Wall and a Foot WallThe Hanging Wall is the one with the slope on

which you could hang. The Foot Wall is the one with the slope on which you could walk.

The type of fault is determined by the motion of the Hanging Wall.

The fault line would also be called the fault plane. The area around it would be called the fault zone.

Is this the Hanging Wall or Foot Wall?

Is this the Hanging Wall or Foot Wall?

The FOOT WALL is the one with the slope you would put your feet on.

Is this the Hanging Wall or Foot Wall?

The HANGING WALL is the one with the slope you would hang from.

Types of Faults

There are several different kinds of faults. These faults are named according to the type of stress that acts on the rock and by the nature of the movement of the rock blocks either side of the fault plane.

Stresses can be compressional (push), tensional (pull) or shear (slide past each other).

The type of stress determines how the Hanging Wall moves and therefore the type of fault.

3 Types of Faults Caused by 3 Different Types of Stress

Normal Fault(Caused by Tension)

Reverse Fault(Caused by Compression)

Transform Fault(Caused by Shear Stress)

Normal Fault

Occurs when tensional stress pulls the fault apart and the Hanging Wall drops.

The fault is an example of tensional strain.

Reverse FaultOccurs when compressional stress

pushes the two parts of the fault together and the Hanging Wall moves up.

The fault is an example of compressional strain.

Transform FaultAKA “strike-slip” faultShear stress causes the parts of the fault

to slide past one another.

This fault is an example of shear strain.

Examples of Faults

FoldsOccur when stress is applied to both ends of

a section of rock or rock layers. Some rocks would break, but a fold occurs when rocks bend. An anticline looks like a “rainbow”; a syncline looks like a “smile”.

Examples of Folds

Your Assignment…

Do the “Lab: Constructing Fault Models”.Color, fold and cut to create the model.

Then use it to answer the questions on the other worksheet. Turn in both parts (be sure your name is on them) today before you leave.

Your test is next class and will include: Layers of Earth, Continental Drift, Seafloor Spreading, Plate Tectonics, Faults and Folds.