1. Crust Deformation: Forces, Faults and Folds

2. Deformation The bending, tilting, and breaking of the earth’s crust major cause of deformation = plate tectonics

3. Isostasy There are two forces involved in changing the earth’s crust: 1. The force of the crust pressing down on the mantle

4. Isostasy 2. The force of the mantle pressing up on the crust. The balancing of these forces is termed Isostasy!

5. Isostatic Adjustments The up and down movements of the crust to reach isostasy are called Isostatic Adjustments

6. Isostatic Adjustments Isostatic Adjustments create pressure causing rocks in that particular area to bend and deform. Common cause of earthquakes!

7. Stress Both isostatic adjustments & plate mov’t cause stress in rocks that make up the crust. Stress = the force that applies pressure to the rocks in the crust

8. Three types of Stress or Forces Compression: occurs when crustal rock is squeezed together

9. Three types of Stress or Forces Tension: occurs when rocks are pulled apart

10. Three types of Stress or Forces Shearing: occurs when rocks are being pushed in two opposite directions

11. What happens because of stress??? Folding & Faulting occurs. When rock responds to stress by becoming permanently deformed w/o breaking, the result is folding.

12. Faulting Because of cooler temperatures & lower pressure near earth’s surface rocks respond to stress by breaking.

13. Faulting When there is no movement in the rocks along a break it is called fracture. When rocks do move at a break it is called a fault.

14. So what’s the REAL difference between folding (bending) and faulting (breaking)? folding faulting

15. Fault terminology Fault plane: the actual break in the rock Hanging wall Foot wall

16. Fault terminology Hanging wall: rock above fault plane that moves relative to rocks below the fault plane Footwall: rock below the fault plane

17. Three types of Faults Normal fault: hanging wall moves down relative to fault plane

18. Three types of Faults Reverse fault: compression causes the hanging wall to move up relative to the foot wall

19. Three types of Faults Strike-slip fault: rock on either side of fault plane move horizontally; usually occur at transform fault boundaries.