Forces in Earth’s Crust

Stress Tension Compression Shearing These forces work over millions of years to change the shape and volume of rock.

Tension Stretches, or pulls the rock apart. Similar to pulling apart a piece of chewing gum.

Compression Squeezes rock until it folds or breaks. Similar to a trash compactor.

Shearing Pushes rock in two opposite directions.

Faults When enough stress builds up in a rock, the rock breaks, creating a fault. Fault- a break in the rock of the crust where rock surfaces slip past each other. Most faults occur along plate boundaries, where the forces of plate motion push or pull the crust so much that the crust breaks.

Foot vs. Hang Block of rock that forms the upper half of a fault. Footwall Hanging wall Block of rock that forms the lower half of a fault. Block of rock that forms the upper half of a fault.

Normal Faults (Click) Caused by TENSION. The hanging wall slides downward as a result of the rock being pulled apart.

Normal Faults Occur where plates diverge, or pull apart (TENSIONS). Rio Grande rift valley in New Mexico.

Normal Fault Question How does a normal fault occur? What type of force causes a normal fault? What happens to the footwall and hanging wall?

Reverse Faults (Click) Caused by COMPRESSION. A fault where the hanging wall slides upward as a result of compression.

Reverse Faults Northern Rocky Mountains

Reverse Fault Question How does a reverse fault occur? What type of force causes a reverse fault? What happens to the footwall and hanging wall?

Strike-Slip Faults (click) Caused by SHEARING. A fault in which rocks on either side move past each other sideways with little up or down motion.

Strike-Slip Fault Transform Boundary- San Andreas fault

Strike-Slip Fault Question San Andreas fault Describe how a strike-slip fault occurs. What force cause it?

Example #1 What type of fault? What type of Stress?

Example #2 What type of fault? What type of Stress?

Example #3 What type of fault? What type of Stress?

Example #4 What type of fault? What type of Stress?

Example #5 What type of fault? What type of Stress? B C

Example #6 What type of fault? What type of Stress? B C

Folding Earth’s Crust Anticline- a fold in rock that bends upward into an arch.

Folding Earth’s Crust Syncline- a fold in rock that bends downward to form a valley.

Describe the difference between an anticline and syncline.

Which letter is an Anticline? Which letter is a Syncline? B