Faults & Earthquakes

1. Faults & Earthquakes Deforming the Earth’s Crust

2. Deformation • The process by which the shape of a rock changes because of stress is called deformation. • There are two basic types of deformation: • Plastic deformation • Elastic deformation • When rock deforms in a plastic manner, it folds like a piece of molded clay. • With elastic deformation, the rock stretches like a rubber band until it breaks. • Elastic deformation can lead to earthquakes.

3. Stress • Stress is a force that acts on rock to change its shape or volume. • Because stress if a force, it adds energy to the rock. • This energy is stored in the rock until the rock either breaks, or changesshape.

4. There are three types of stress that occur in the Earth’s crust: • Compression • Tension • Shearing

5. Compression • The stress force called compression squeezes rock until it folds, or breaks. • Compression makes a mass of rock occupy a smallerspace. • When compression occurs at a convergent boundary, large mountainranges can form.

6. Tension • The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle. • Tension occurs where two plates are moving apart, such as mid-ocean ridges, or rift valleys.

7. Shearing • Stress that pushes a mass of rock in two opposite, horizontal directions is called shearing. • Shearing can cause rock to break and slipapart. • Shearing occurs at transform boundaries.

9. Folding • The bending of rock layers because of stress in the Earth’s crust is called folding. • Undisturbed rock layers are horizontal, so when we see a fold we know that deformation has taken place.

10. Folds • The two most common types of folds are: • Anticlines • Synclines • Anticlines are upward-arching folds. • Synclines are downward, trough-like folds. • Another type of fold is a monocline. • In a monocline, both ends of the fold are horizontal.

11. Faults • When the stress on rocks causes them to break and slip past each other, a fault is formed. • The blocks of crust on each side of the fault are called faultblocks. • When faults are not vertical one side of the fault block will be called a hangingwall and the other the footwall. • The position of the fault block will determine which it is.

12. Faults • Normal fault • There are 3 main types of faults: Reverse Fault • Reverse, or thrust fault • Strike-slip

13. Normal Faults • The hanging wall lies above the fault and the footwall lies below the fault. • Tension forces cause normal faults. • When movement occurs along the fault line, the hanging wall slips downward. • Normal faults are found at divergent plate boundaries, where plates pullapart.

14. Reverse Faults • Compression forces produce reverse faults. • Reverse faults have the same basic structure as a normal fault, but the blocks move in the opposite direction. • When movement occurs along the fault line, the hanging wall slides up and over thefootwall. • Reverse faults are found at convergent plate boundaries, where plates are pushed together.

15. Strike Slip Faults • Shearing creates strike-slip faults. • The rocks on either side of the fault slip past each other sideways with little up or down motion. • A strike-slip fault that forms the boundary between two plates is called a transform boundary.

16. Fault Block Mountain • When the tension in a normal fault uplifts a block of rock, a fault-block mountain forms. • The Grand Tetons in Wyoming are an example of a fault-block mountain range.

17. Folded Mountains • Folded mountains form at convergent boundaries where continents have collided. • The Appalachian Mountains, the Alps, and the Himalayas are examples of folded mountains.